Taxonomic revision of the Mexican Eucyclops (Copepoda: Cyclopoida) with comments on the biogeography of the genus

ABSTRACT Based on the examination of specimens deposited in different national and international biological collections, we reviewed the ca. 800 records of the genus Eucyclops in Mexico and compared them with the type material of presumedly widespread species. Resulting from our taxonomical analysis, in this contribution we recognise 17 species dwelling in Mexico. Complementary upgraded descriptions of eight species emphasising newly introduced taxonomic characters are also presented from the examination of Mexican specimens. These species include E. elegans, E. prionophorus, E. festivus, E. leptacanthus, E. torresphilipi, E. chihuahuensis, E. cuatrocienegas and the recently described E. tziscao and E. angeli. In addition, the use of upgraded descriptive standards involving new morphological characters allowed the discovery of six new species that are described in this work: E. alekseevi sp. nov., E. wixarica sp. nov., E. defayeae sp. nov., E. mittmanni sp. nov., E. estherae sp. nov. and E. ishidai sp. nov. Most of these species were previously recorded in Mexico under different names. The occurrence of E. pectinifer, E. elegans, E. prionophorus and E. leptacanthus in Mexico is herein confirmed. We propose the ornamentation patterns of the fourth swimming legs (i.e. basipodite, coxal plates) as reliable additional characters to recognise closely related species of Eucyclops. The importance of the antennal basis ornamentation in the taxonomy of the genus is supported by our data. We evaluated the taxonomic value of 113 morphometric and binary characters using statistical methods; results of this analysis showed that morphometric characters alone overlap and thus have a limited value to distinguish species of Eucyclops. We include comments on E. serrulatus s. str. in order to provide a complete comparison frame among members of the serrulatus-species complex, but we did not find the strict form in the samples examined. A key to the Mexican species of the genus is also provided.


Introduction
Until recently the systematics of the free-living Cyclopidae was based on a limited number of morphological characters, some of which have been proved to be highly variable and related to environmental factors (Dahms and Fernando 1997;Rocha 1998; many cases, these characters have been insufficient to distinguish closely related species in the genus, a situation that has favoured a complex taxonomic history that includes many species or records that remain under an uncertain status (Collado et al. 1984;Reid 1985;Ishida 1997;Suárez-Morales 2004). Ishida (1997Ishida ( , 2001Ishida ( , 2002Ishida ( , 2003, Alekseev et al. (2006), Alekseev (2008Alekseev ( , 2010 and Alekseev and Defaye (2011) pioneered interesting attempts to solve the taxonomic problems in the genus. Ishida's works focused on the species complex 'serrulatus-like species' and 'speratus-like species' from Japan. Alekseev and collaborators emphasised the study of the 'serrulatus-group'. These authors incorporated new characters such as the antennal ornamentation patterns, the ornamentation of mouthparths, the patterns of body pores and even the ornamentation of the coxal plates, the basipods and coxopods of the fourth swimming leg. Overall, some problems have been solved, but new characters remain to be explored in order to strengthen the taxonomy of the genus.
In the Americas, there are more than 800 records of the genus that have been assigned to 31 nominal species. Approximately 300 of these records are related to taxonomically conflictive taxa (i.e. E. serrulatus, E. agilis, E. speratus). These records should be reviewed and eventually reassigned to American forms or, alternatively, confirm the presence of European species in this continent. Currently, Mexico is the country with the most records of Eucyclops (460) in the Americas, which currently involve 18 species: E. agilis (synonym of E. serrulatus), E. bondi, E. breviramatus, E. chihuahuensis, E. conrowae, E. cuatrocienegas, E. delachauxi, E. elegans, E. festivus, E. leptacanthus, E. pectinifer, E. prionophorus, E. pseudoensifer, E. serrulatus (possibly E. pectinifer), E. speratus (E. elegans in the Americas), E. torresphilipi and the recently described E. tziscao and E. angeli (Juday 1915;Pearse and Wilson 1938;Osorio-Tafall 1943;Comita 1950;Lindberg 1955;Suárez-Morales et al. 1985;Zamudio-Valdéz 1991;Zanatta-Juárez 1995;Dodson and Silva-Briano 1996;Grimaldo-Ortega et al. 1998;Suárez-Morales and Reid 1998;Gutiérrez-Aguirre 1999;Álvarez-Silva and Gómez-Aguirre 2000;Elías-Gutiérrez 2000;Fiers et al. 2000;Rodríguez-Almaráz 2000;Suárez-Morales 2004;Elías-Gutiérrez et al. 2008;Jiménez-Trejo and Vásquez-Vargas 2008;Mercado-Salas 2009;Suárez-Morales and Walsh 2009;Gutiérrez-Aguirre et al. 2013). Based on the complexity of the genus and the lack of revisionary efforts in Mexico and in the Neotropical region as well, Suárez-Morales (2004), Suárez-Morales and Walsh (2009) and Gutiérrez-Aguirre et al. (2013) argued that the Mexican diversity of the genus could be underestimated. According to observations from Grimaldo-Ortega et al. (1998), Elías-Gutiérrez (2000), Rodríguez-Almaráz (2000), Suárez-Morales (2004), Suárez-Morales and Walsh (2009), Mercado-Salas (2009) and Gutiérrez-Aguirre et al. (2013), the morphology of the Mexican specimens shows some variations with respect to original descriptions and records. These variations suggest that undescribed species have been recorded over time under the names of 'common', 'widespread' or 'cosmopolitan' species. These observations highlight the importance of performing a complete morphological study of the species and records from Mexican water bodies including the re-examination and redescription of type material and the revision of voucher specimens supporting Mexican records in national or international collections. This process is expected to allow a re-evaluation of the variability among Mexican populations by using new characters that could aid us to achieve an accurate morphological delimitation of the Mexican species and allow reliable taxonomical identifications. The goal of this survey is to provide the bases of a new taxonomical approach to identify species of Eucyclops. This will contribute to (1) solving the taxonomy and diversity of the genus in Mexico, (2) assessing and clarifying the real distributional patterns of the species and (3) marking an upgraded standard in the description model in the taxonomy of the genus in the Americas.

Methods
In order to have a complete overview of the taxonomic status of the Mexican material, we examined type and non-type specimens deposited in different collections: Staatliches Museum für Naturkunde, Karlsruhe (E. delachauxi, E. prionophorus, E. bondi, E. leptachantus and specimens of E. elegans); Muséum National d´Histoire Naturelle, Paris (E. pseudoensifer); National Museum of Natural History Smithsonian Institution in Washington, DC (E. conrowae and specimens of E. elegans); and El Colegio de la Frontera Sur (E. torresphilipi, E. cuatrocienegas, E. chihuahuensis, E. tziscao, E. angeli). The redescriptions of species and additional comparative comments on specimens from the first three collections can be consulted in Suárez-Morales (2014a, 2014b). Taxonomic and morphological remarks on the Mexican type specimens deposited at El Colegio de la Frontera Sur are included in this work. A thorough search was performed to locate the collections where Mexican material is deposited; the two main collections where Mexican specimens are deposited are: (1) the National Museum of Natural History Smithsonian Institution, which holds a number of records from the states of Quintana Roo and Nuevo Leon; and (2) El Colegio de la Frontera Sur, which holds the most important collection of Eucyclops (and copepods in general) from Mexico, including records from 10 states: Aguascalientes, Chihuahua, Chiapas, Coahuila, Durango, San Luis Potosi, State of Mexico, Tabasco, Quintana Roo and Zacatecas. From only these two collections we reviewed more than 300 specimens. Additional biological samples from Baja California, Baja California Sur, Oaxaca, Coahuila and Sinaloa deposited at the Centro de Investigaciones del Noreste (CIBNOR) and samples from the states of Queretaro, Veracruz and Oaxaca held at the FES-Iztacala Universidad Nacional Autonoma de Mexico (UNAM), Mexico City, were also examined, aiming to expand the geographic coverage of this survey.
All specimens from ECOSUR, CIBNOR and UNAM were dissected and appendages mounted in glycerin for taxonomic analysis. For each slide/specimen examined, a sheet with morphometric measurements was filled in to have a detailed record of the morphological variation of each species. The appendage and body morphology, measurements and micropatterns analysed in each specimen followed Einsle (1985), Karaytug (1999), Alekseev et al. (2006) and Alekseev and Defaye (2011), all with slight modifications (see Figure 1).
The following morphological characters (with abbreviations) were examined and evaluated in most of the studied material.
For P1, size of basipodal spine and relative lengths of distal segment of Enp and apical spine; for Enp3 P4, relative length, width and size of apical spines, insertion of lateral seta and ornamentation of coxal spine ( Figure 1O); for P1-P4, micropatterns on caudal side of coxopodite, micropatterns on frontal and caudal surfaces of intercoxal sclerites, and number of modified setae in Enp and Exp (see Figure 1F-N); (4) Leg 5 (P5): relative length of inner spine, segment and two setae; (5) Genital double somite (GDS): shape of seminal receptacle; (6) Anal somite: shape of anal operculum; (7) Caudal rami: length/width ratio; percentage of spinule coverage of outer margin and size of spinules; length ratio of caudal setae. Caudal setae labeled as follows: IIanterolateral (lateral) caudal seta; IIIposterolateral (outermost) caudal seta; IVouter terminal (terminal median external) caudal seta; Vinner terminal (terminal median internal) caudal seta; VIterminal accessory (innermost) caudal seta; VIIdorsal seta; nomenclature follows Huys and Boxshall (1991), Dussart and Defaye (1995) and Alekseev and Defaye (2011) (Figure 1P). In males: (1) Antennule (A1): number of segments and number of elements present on each segment, following Karaytug and Boxshall (1999); (2) Antenna (A2): micropatterns on frontal and caudal sides of basipodite, as in females; (3) Fourth leg (P4): for Enp3, relative length, width and size of apical spines, relative percentage of lateral seta insertion and ornamentation of coxal spine; micropatterns of caudal side of coxopodite, micropatterns of frontal and caudal sides of intercoxal sclerites and number of modified seta in Enp and Exp (as in females); (4) Legs 5 and 6 (P5, P6): relative length of inner spine, segment and setae of both legs and relative length of spine of P6 relative to urosomites; (5) Caudal rami: length/width ratio; percentage of outer margin cover with spinules and size of spinules; length ratio of the caudal setae. Caudal setae nomenclature as in female. Drawings of dissected specimens were prepared using an Olympus-BX53 microscope equipped with a camera lucida at a magnification of 1000×. Type specimens were deposited in the collection of Zooplankton held at El Colegio de la Frontera Sur (ECOSUR), Chetumal, Mexico (ECO-CH-Z).
For those species of which several specimens were available, one or two individuals were prepared for scanning electron microscopy (SEM) examination. This analysis was performed with a JEOL LV-5900 microscope at facilities of the Universidad Autónoma de Aguascalientes, Mexico. The SEM processing included dehydration in progressively higher ethanol concentrations (60, 70, 80, 96, 100%), drying and gold coating following standard methods.
In order to provide a general evaluation of the characters measured as a tool to separate the species examined in this survey, we used different statistical methods.
These included boxplot graphics for morphometrical characters, correlation between morphometric values, and a cluster analysis (Euclidean distances-similitude). These were performed with the aid of the R-Development Core Team (2008) sofware. The matrix data used in these analyses included 113 characters (morphometric and binaries). Characters were codified as follows: (1) TB (total body length): value in millimeters.

Description
Female. Habitus as in Figure 5A. Average length excluding caudal setae = 1061 µm. Whole body (caudal rami included) ornamented with small pits (see Figure 2A, 5). Prosome representing 58% of total body length, symmetrical in dorsal view. Prosomal fringes finely serrate in dorsal view ( Figure 5B). Urosomal fringes strongly serrate. Genital double somite symmetrical ( Figure 5D), representing 10% of total body length; proximal third of genital double somite expanded laterally. Seminal receptacle with rounded lateral arms on posterior margin, typical of the serrulatus-complex. Anal operculum slightly rounded, weakly serrate ( Figure 5F). Length/width of caudal rami = 7.0; inner margin of caudal ramus naked; outer margin with strong spinules covering 60% with respect to the total length of ramus. Dorsal seta (VII) 0.4 times as long as caudal ramus and 0.7 times as long as outermost caudal seta (III). Length ratio of innermost caudal seta (VI)/outermost caudal seta (III) = 1.2. Lateral caudal seta (II) inserted at 70% of ramus.
Leg 5 ( Figure 8F). Free segment subrectangular, 1.9 times longer than wide, bearing strong inner spine and two setae; medial seta 1.7 times longer than outer seta and 1.4 times longer than inner spine. Inner spine 2.6 times longer than segment.
Legs 1-4. Enp and Exp of all swimming legs three-segmented, armed as in females.
Leg 6 ( Figure 4L). Represented by small, low plate adjacent to lateral margin of genital somite armed with strong inner spine and two unequal setae. Inner spine reaching medial margin of third urosomite, as long as medial seta and 1.6 times longer than outer seta. Small, strong spinules present at insertion of inner spine.
Remarks. Eucyclops elegans was recently assigned as a member of the serrulatus-group by Mercado-Salas and Suárez-Morales (2014b) following the diagnostic characters established by Alekseev and Defaye (2011) to distinguish species of this group. The inclusion of E. elegans in the serrulatus-group precludes the idea of a synonymy with E. speratus and supports Reid and Marten's (1995) assumption that American records of E. speratus should be assigned to E. elegans after an analysis of more material. It is important to consider that we observed differences between specimens of E. elegans from North and South America; the latter population could refer to another species (see Mercado-Salas and Suárez-Morales 2014b). We described a new species closely related to E. elegans (see remarks of E. mittmanni sp. nov.) from Mexico that must be considered in the identification of material related to E. elegans. Eucyclops elegans can be distinguished from E. serrulatus by the ornamentation of the frontal surface of the antennary basis: group N18, N1 and N2 are fused and row 22 is present on the caudal surface. Both species share rows N3, N4, N5, N15 and N17 on the frontal surface. The caudal surface of the antennary basis has some additional differences between these two species: row N8 is absent in E. serrulatus and sometimes N16 is absent too, but in E. elegans both rows are always present. The sixth leg of males of E. elegans is remarkably different from that of E. serrulatus, E. speratus, E. neumani titicacae, and most of the American species of the genus: it bears a small but strong inner spine which barely reaches the medial margin of the third urosomite, while in the rest of the species this spine is clearly longer than both the medial and outer setae and reaches at least the posterior margin of the third urosomite. Furthermore, the proportions of the P6 setae and spine should be considered important in separating the populations examined; together with the antennule ornamentations, this character was useful to distinguish species. Other American Eucyclops with long caudal rami are E. neumani s. str. and E. neumani titicacae, both differing from E. elegans because the caudal ramus only bears spinules in the area adjacent to the lateral caudal seta (II). Among other characters, the former subspecies (E. neumani s. str.) differs from E. elegans, E. serrulatus and E. neumani titicacae in details of the antennary ornamentation, with group N1 formed by spinules and not hair-like elements. Eucyclops neumani titicacae also differs from E. elegans and E. serrulatus in its unique ornamentation pattern of the intercoxal plate of P4 (see Figure 13 Kiefer 1957a; Fuentes and Suárez-Morales 2014). Kiefer, 1931b (Figures 9-13) Description Female. Habitus as in Figure 11A. Average length excluding caudal setae = 688 µm. Prosome representing 58% of total body length, symmetrical in dorsal view. Prosomal fringes finely serrate in dorsal view. Urosomal fringes strongly serrate. Genital double somite symmetrical ( Figures 9A, 11B), representing 11.3% of total body length; proximal third of genital somite expanded laterally. Seminal receptacle with rounded lateral arms, posterior margin with sinuous sac ( Figure 9A). Anal operculum slightly rounded, smooth ( Figure 9B). Length/width of caudal rami = 3.9; inner margin of caudal ramus naked; outer margin with strong spinules covering 55% with respect to the total length of ramus. Dorsal seta (VII) 0.5 times as long as caudal ramus and 0.9 times as long as outermost caudal seta (III). Ratio of innermost caudal seta (VI)/outermost caudal seta (III) = 1.1. Lateral caudal seta (II) inserted at 74% of caudal ramus.
Leg 1 ( Figures 10A, 12D-E). Frontal surface of intercoxal sclerite with row of hair-like elements arranged in a semicircular pattern on each side, caudal surface with row I bearing 10 minute spinules and row II with 24 minute spinules. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C. Inner basal seta (basipodal spine) reaching middle margin of Enp3, 0.8 times as long as Enp. Length/width ratio Enp3 = 1.6, apical spine of Enp3 as long as Enp3 (1.0).
Leg 2 ( Figure 10B-C). Frontal surface of intercoxal sclerite with row I bearing hair-like spinules arranged in a circular pattern; caudal surface with rows I and II close to each other, forming a group in a position where group II is usually found, with minute spinules. Distal margin of intercoxal sclerite with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula A-B-C-D.    Leg 5 ( Figures 9A, 13F). Free segment subrectangular, 1.5 times longer than wide, bearing one strong inner spine and two setae; medial seta 1.4 times longer than outer seta and 1.6 times longer than inner spine. Inner spine 1.9 times longer than segment.
Male. Not found.
Remarks. In Kiefer's (1931a) original description, the ornamentation of the outer margin of the caudal rami, with spinules increasing in size distally, and the remarkably strong spine of the fifth leg were advanced as the main characteristics to distinguish this species. Both characters were found in the Mexican specimens identified as E. prionophorus. This species was studied by Einsle (1992) based on type material and additional records deposited in Kiefer's collection and recently also by Mercado-Salas and Suárez-Morales (2014b). This species differs from its congeners by the possession of a dorsal caudal seta shorther than both the innermost and outermost caudal setae, a P1 basipodal seta reaching the middle margin of Enp3, and the modified setae of Exp of P3 and P4, which are heavily chitinised and distally blunt. This species differs from E. bondi and E. conrowae by its possession of a relatively smaller caudal dorsal seta and in the ornamentation of the fourth coxal plate, in which row I is represented by long and strong spinules, whereas it is formed by small and stronger spinules in the other two species. There are additional differences in rows I and II; in the former two species these rows are always continuous, with short and strong spinules, but in in E. prionophorus both rows are present only adjacent to the outer margins and are represented by long hair-like spinules. As stated by Alekseev and Defaye (2011), E. prionophorus belongs to the serrulatus-group, a notion that we are able to support with the additional data on the ornamentation of the antennal basis. In addition, we observed that in some of the Mexican specimens the seminal receptacle differs from that observed in specimens from Kiefer's collection but also from those depicted by Einsle (1992) and Mercado-Salas and Suárez-Morales (2014a). These specimens have a typical seminal receptacle of the serrulatus-group, but in some Mexican specimens the posterior margin has a sinuous sac. Another difference between the Mexican E. prionophorus and the type material was the length/width proportion of Enp3 of all swimming legs, which is slightly longer in the Mexican material. Eucyclops prionophorus can be easily distinguished from E. serrulatus by the possession of small spinules on row N2 on the frontal surface of the antennal basis and also by the presence of rows N18 (frontal surface), N10, N16 and N22 (caudal surface), absent in E. serrulatus. It differs from E. pectinifer by the absence of N6 and the presence of N22 (absent in E. pectinifer); both species share the absence of N13 and the presence of row N1. Spinules of row N12 have the same size in E. prionophorus while some spinules are clearly longer than the others in E. pectinifer. The ornamentation patterns of the caudal surface of the intercoxal sclerites of E. prionophorus differ from those of both E. pectinifer and E. serrulatus. In P1, rows I and II of E. prionophorus bear minute spinules whereas row I is absent and row II bears long hair-spinules in the other two species. In P2 of E. prionophorus rows I and II has minute spinules and both are closer to each other than in other related species. In E. serrulatus and E. pectinifer row I is absent and row II is, as in P1, formed by long spinules. The caudal surface of the intercoxal sclerite of P3 has some additional differences among these three species. In E. pectinifer row I bears long hairs and a gap at the middle margin, row II and III are continuous and armed with long hair-spinules; in E. serrulatus row I bears long hair spinules and a gap in the middle margin as well, row II is continuous, with small spinules, row III bears long, strong spinules only in the outer margins (gap in middle section); and in E. prionophorus row I bears long hairs with a small gap at middle margin, row II is continuous and bears strong spinules, those adjacent to the outer margins are longer than those in the middle, and row III is continuous, with strong spinules, while the spinules on the outer margins are longer. The fourth leg sclerite ornamentation differs among these species: in E. pectinifer and E. serrulatus row I bears remarkably long spinules while in E. prionophorus these spinules are long but shorter than in the other species, rows II and III fit well in the variation pattern described by Alekseev et al. (2006) and Alekseev and Defaye (2011) for E. serrulatus and E. pectinifer. In E. prionophorus row F is present in the coxal surface, like in E. pectinifer, but this row is absent in E. serrulatus.
Leg 2 ( Figures 15C-D, 18A-B). Frontal surface of intercoxal sclerite with row I bearing hair-like elements arranged in a circular pattern; caudal surface with row I discontinuous, bearing 7-9 small spinules on each side, row II continuous with 24-30 small spinules. Distal margin of intercoxal sclerite with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula A-B-C-D. Length/width ratio of Enp3 = 2, apical spine of Enp3 1.2 times as long as Enp3.
No modified setae present.
. Frontal surface of intercoxal sclerite armed with group of long hairs on each side; caudal surface with row I bearing long hairs and with a small gap in the middle, row II continuous bearing 30-32 small spinules and row III continuous bearing 32-37 spinules. Distal margin with two rounded, chitinised projections. Coxa with strong, biserially setulated inner coxal seta, basally with long hairs and distally with a small gap in the middle margin; row II continuous, with strong spinules, outer margins bearing more spinules than medial margin; and row III divided into three sections, two on outer margins with strong and long spinules and medial margin with 3-4 long spinules. Frontal surface of coxa with row of small spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; inner margin with long hairs on proximal section and strong spinules distally; outer edge with one distal spinule and proximal hair-like elements, gap in the middle margin. Length/width ratio Enp3 = 2.5, length ratio inner spine of Enp3/length Enp3 = 1.2; length ratio outer spine of Enp3/ length Enp3 = 0.9; proportion inner/outer spines Enp3 = 1.3. Lateral seta of Enp3 inserted at 68% of segment. No modified setae in Enp and Exp.
Leg 5 ( Figure 19B). Free segment subrectangular, 2.1 times longer than wide, bearing one strong inner spine and two setae; medial seta 1.8 times longer than outer seta and 1.6 times longer than inner spine. Inner spine twice longer than segment.
Remarks. As mentioned by Gutiérrez-Aguirre et al. (2013), E. festivus has been recorded in north and central Mexico and recently also from a pond in the state of Chiapas in southeast Mexico. This species appears to be related to E. estherae sp. nov. and E. wixarica sp. nov., both described herein. Differences among these species are presented in the remarks sections of E. wixarica sp. nov. and E. estherae sp. nov.
Leg 2 ( Figure 23D-E, 25E). Frontal surface of intercoxal sclerite with row I bearing long hair-like elements arranged in circular pattern; caudal surface with row II continuous, with 20 minute spinules, row I absent. Distal margin of intercoxal sclerite with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with row I bearing strong small spinules, row II with strong spinules adjacent to outer margins and row III with strong, long hair-like spinules adjacent to outer margins. Frontal surface of coxa with row of small spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; proximal inner margin with long hairs; distal section with strong spinules, outer margin with three distal spinules and with hairs on proximal section, gap in middle margin. Spinule formula on the caudal surface = A-B-C + D-E-F-G-J. Length/width ratio Enp3 = 2.7, length ratio inner spine of Enp3/length Enp3 = 1.1; length ratio outer spine of Enp3/length Enp3 = 0.9; proportion inner/outer spines Enp3 = 1.2. Lateral seta of Enp3 inserted at 61% of segment. Modified setae in Enp and Exp.
Leg 5 ( Figure 26F). Free segment subrectangular, 1.9 times longer than wide, bearing one slender inner spine and two setae; medial seta 1.7 times longer than outer seta and 2.3 times longer than inner spine. Inner spine 1.7 times longer than segment.
Male. Not found.
Remarks. Based on our observations, we herein assign E. leptacanthus as a member of the serrulatus-group. A distinguishing character of this species is the presence of long hair-like spinules on N1, while this row possesses long hairs in all the other members of the group. We identified our specimens from Mexico as E. leptacanthus because it has the main morphologic and morphometric characters found in the holotype from Kiefer's collection. This species is characterised by a long innermost caudal seta (VI) which is 1.3 times longer than the outermost caudal seta (III), long setae in the four swimming legs and a slender P5 spine. Among its congeners, E. leptacanthus can be easily distinguished from E. bondi by the possession of a shorter dorsal seta and a completely different ornamentation of the P4 intercoxal sclerite. Eucyclops leptacanthus resembles E. prionophorus, E. serrulatus and E. pectinifer but shows significant differences with respect to these species. In E. leptacanthus row N1 of the antennal Bsp has long hair-spinules, while in E. prionophorus, E. serrulatus and E. pectinifer this row bears long hair-like elements. In addition, N6 is absent in E. leptacanthus as it is in E. prionophorus and E. serrulatus, but it is present in E. pectinifer. The caudal surface of the antennal Bsp of E. leptacanthus resembles both E. prionophorus and E. pectinifer in the presence of row N18, but differs from both species by the unique presence of N13. The caudal surface of the coxal sclerite of the four swimming legs differs among these species as well. In P1 E. leptacanthus shares with E. serrulatus and E. pectinifer the absence of row I but differs from both species in its possession of a row II with minute spinules; it has long hairs in the other species and in E. prionophorus row I is always present. In P2, E. leptacanthus shares the absence of row I with E. serrulatus and E. pectinifer but differs in having row II with minute spinules vs long spinules in the other two species. Also, E. prionophorus differs by possessing a row I armed with minute spinules. The caudal surface of the P3 intercoxal sclerite is similar in the three species, but row II of E. leptacanthus is discontinuous, thus differing from the continuous pattern observed in E. prionophorus, E. serrulatus and E. pectinifer. The ornamentation pattern of the caudal surface of the P4 sclerite is similar in all species; in E. leptacanthus it has small but strong spinules on row I, whereas this row bears long spinules in the other species.

Description
Female. Average length excluding caudal setae = 680 µm. Prosome representing 66% of total body length, symmetrical in dorsal view. Prosomal fringes finely serrate in dorsal view. Urosomal fringes strongly serrate; posterior margin of anal somite with row of spinules. Genital double somite symmetrical, representing 16.5% of total body length; proximal third of genital double somite expanded laterally. Seminal receptacle with rounded, lateral arms on posterior margin, typical of the serrulatus-complex but posterior lobe slightly expanded. Anal operculum slightly rounded and smooth, with a small gap in the middle margin ( Figure 27A). Length/width of caudal rami = 4.1; inner margin of caudal ramus smooth; strong spinules covering 47% with respect to the total length of ramus. Dorsal seta (VII) 0.7 times as long as caudal ramus, and 1.0 times as long as outermost caudal seta (III). Ratio of innermost caudal seta (VI)/outermost caudal seta (III) = 1.6. Lateral caudal seta (II) inserted at 77% of total length of caudal ramus.
Leg 2 ( Figure 27E-F). Frontal surface of intercoxal sclerite with row I bearing hairs arranged in semicircular pattern; caudal surface lacking row I, row II continuous, with 21 strong spinules. Distal margin of intercoxal sclerite with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C-D. Length/width ratio of Enp3 = 2.0, apical spine of Enp3 1.2 times as long as Enp3. No modified setae present.
Leg 3 ( Figure 27G-H). Frontal surface of intercoxal sclerite with hairs-spinules arranged in circular pattern on each side; caudal surface with row I bearing long hairs (gap at middle section), row II with 24 strong spinules, divided into two sections arranged in semicircular pattern; row III continuous, with 19 strong spinules. Distal margin with two rounded, chitinised projections. Coxa with strong biserially setulated inner coxal seta, proximal section with long hairs; distal section with strong spinules long both margins. Caudal coxal surface with spinule formula = A-B-C. Length/width ratio of Enp = 2.3, apical spine of Enp3 being 1.0 times as long as Enp3. No modified setae present.
Leg 4 ( Figure 27I-J). Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface of sclerite with row I bearing small hair-spinules arranged in a semicircular pattern, caudal surface with row I bearing long, strong spinules, row II with spinules close to outer margins of sclerite; row III with strong and slightly longer spinules close to outer margins. Frontal surface of coxa with row of small spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; proximal inner margin with long hairs; distal margin with strong spinules; outer margin with one distal spinule, proximal section with setules, gap in middle margin. Spinule formula on caudal surface = C + D-G-H-J. Length/width ratio Enp3 = 2.1, length ratio inner spine of Enp3/length Enp3 = 1.2; length ratio outer spine of Enp3/length Enp3 = 0.8; length ratio inner/outer spines Enp3 = 1.5. Lateral seta of Enp3 inserted at 70% of segment. No modified setae in Enp and Exp.
Leg 5. Free segment subrectangular, 1.6 times longer than wide; bearing one strong inner spine and two setae; medial seta 1.6 times longer than outer seta and 1.6 times longer than inner spine. Inner spine twice longer than segment.
Male. Length range excluding caudal setae = 652 µm. Prosome symmetrical in dorsal view, representing 67% of total body length. Urosome six-segmented, slightly elongated, urosomal fringes strongly serrate. Caudal ramus smooth along both inner and outer margins, with strong spinules at insertion of lateral seta.
Legs 1-4. End and Exp of all swimming legs three-segmented and armed as in female.
Leg 5. Free segment subrectangular, 1.7 times longer than wide, bearing one inner spine and two setae; medial seta longer than outer seta (about 1.6 times) and inner spine (1.5 times). Inner spine 1.5 times longer than segment.
Remarks. As stated by Suárez-Morales (2004), E. torresphilipi resembles the South American species E. leptacanthus and E. delachauxi because they share a particularly slender inner P5 spine and relatively short caudal rami. The morphometric values obtained from our analysis of E. leptacanthus and E. torresphilipi revealed that there are no significant differences between these species, but the ornamentation of the swimming legs and the antennae provide useful characters to distinguish them. In the P1 coxa of E. torresphilipi row C bears long hair-spinules whereas this row has small but strong spinules in E. leptacanthus. In the P2 coxa small differences were found: row D of E. torresphilipi bears long hair-spinules but in E. leptacanthus this row has strong and long spinules which are also fewer than in E. torresphilipi. In P3 differences in the caudal surface of the intercoxal sclerite are remarkable; in E. leptacanthus row I bears long hairs while in E. torresphilipi this row is armed with long hair-spinules. In both species row II is divided in two sections, each close to the outer margin, but in E. leptacanthus it has small but strong spinules whereas in E. torresphilipi this row covers all the medial surface of the intercoxal sclerite and bears strong and slightly longer spinules. In both species row III has long spinules along the sclerite. Eucyclops prionophorus is another species that seems to be closely related to E. torresphilipi but can be easily distinguished because of its possession of row I on the caudal surface of P1 and P2 intercoxal sclerites; this row is absent in E. torresphilipi. One of the main characteristics of E. torresphilipi is the coxal ornamentation of the fouth swimming leg which is remarkably reduced when compared with that known in other congeners like E. delachauxi, E. leptacanthus, E. prionophorus, E. pectinifer and E. bondi. In E. torresphilipi row A is not present as it is in all the other mentioned species, but also E. torresphilipi presents a unique pattern in row J which is divided into three rows bearing minute spinules. This pattern is similar to that present in E. albuferensis from Spain (Alekseev 2008), with the difference that in E. albuferensis the groups of spinules are not clearly separated as they are in E. torresphilipi. Another distinctive feature of E. torresphilipi is the shape of its anal operculum; in the Mexican Eucyclops we found two general types: (1) rounded and smooth and (2) rounded and serrate (E. elegans, E. tziscao and E. defayeae sp. nov.); E. torresphilipi is the only species whose anal operculum is smooth and rounded but has a small gap in its middle section. This character is known only in E. neumani s. str., a South American species and otherwise clearly different to E. torresphilipi because of the ornamentation of the caudal rami, the length/width of the caudal ramus, and the body size, among other characters.
Eucyclops delachauxi and E. torresphilipi share a short caudal ramus and a particularly long lateral seta in Enp3 P4 as compared to other species of Eucyclops. In these two species this seta reaches or exceeds the apical margin of the outer spine, while in the rest of the species the seta does not reach beyond the midlength of the outer spine. A character that separates these two species is the ornamentation of the outer margin of the caudal ramus; in E. torresphilipi (as in most of species of the genus) spinules cover ¾ of the total length of the ramus, while in E. delachauxi the serra is reducedit covers only 20-30% of the outer margin.  Antennule. Tip reaching midlength of third pediger. Armature per segment as follows: 1(8s), 2(4s), 3(2s), 4(6s), 5(2s), 6(1s+1sp), 7(2s), 8(3s), 9(2s+1ae), 10(2s), 11(2s+1ae), 12(7s +1ae). Two transverse rows of spinules on first segment, first row with strong spinules and adjacent second row with minute spinules. Spine on sixth segment reaching midlength of seventh segment.
Leg 1 ( Figure 28C-E). Frontal surface of intercoxal sclerite with row I bearing long spinules arranged in semicircular pattern on each side, caudal surface with row II bearing long hair-spinules, row I absent. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C. Inner basal seta (basipodal spine) not reaching midlength of Enp3, 0.6 times as long as Enp. Length/width ratio Enp3 = 1.5, apical spine of Enp3 being 1.1 times as long as Enp3.
Leg 2 ( Figure 28F-G). Frontal surface of intercoxal sclerite with row I armed with hairs arranged in circular pattern; caudal surface with rows I and II continuous, both bearing long hair-spinules. Distal margin of intercoxal sclerite with two rounded chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C-D. Length/width ratio of Enp3 = 1.9, apical spine of Enp3 1.3 times as long as Enp3. No modified setae present.
Leg 3 ( Figure 28H-I). Frontal surface of intercoxal sclerite armed with hairs arranged in circular pattern on each side; caudal surface with row I bearing long hairs (gap at middle section), rows II and III continuous, bearing long hairs. Distal margin with two rounded, chitinised projections. Coxa with strong biserially setulated inner coxal seta, proximal section with long hairs; distal section with strong spinules along bothmargins. Caudal coxal surface with spinule formula = A-B-C. Length/width ratio of Enp = 2.0, apical spine of Enp3 being 1.2 times as long as Enp3. No modified setae present. Leg 4 ( Figure 28J-M). Distal margin with two low, rounded, chitinised projections. Frontal surface of intercoxal sclerite with row I bearing long hairs arranged in semicircular pattern, caudal surface of intercoxal sclerite with row I bearing long hairs, row II with long hair-spinules on outer margins and row III with long hair-spinules on outer margins. Frontal surface of coxa with row of small spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; inner margin with long setules proximally and with strong spinules distally, outer margin with setules along proximal section and distally naked. Spinule formula on caudal surface = A-B-C + D-E-F-G-J. Length/width ratio Enp3 = 2.5, length ratio inner spine of Enp3/length Enp3 = 1.1; length ratio outer spine of Enp3/length Enp3 = 0.9; length ratio inner/outer spines Enp3 = 1.3. Lateral seta of Enp3 inserted at 68% of segment. No modified setae in Enp and Exp.
Leg 5. Free segment subrectangular, 1.5 times longer than wide, bearing one strong inner spine and two setae; medial seta 2.8 times longer than outer seta, twice as long as inner spine. Inner spine 2.2 times longer than segment.

Male. Unknown.
Remarks. When this species was described (Suárez-Morales and Walsh 2009), it was related and compared to E. pseudoensifer; however, even when the general shape and main proportions are similar to E. pseudoensifer, our analysis revealed that they belong to different groups. Eucyclops pseudoensifer was redescribed by Suárez-Morales and Walsh (2009) and new morphological data consulted in Dussart Collection (pers. obs. Mercado-Salas, 2012), mainly in reference to the ornamentation patterns of the swimming legs and antennal basis. Eucyclops pseudoensifer is not a member of the serrulatusgroup because of the lack of N1 and N2 in the antennal basis while both rows N1 and N2 are present in E. chihuahuensis, the former bearing long hair-spinules and N2 with small but strong spinules. This character places this species in the serrulatus-group. It appears to be more closely related to E. pectinifer and E. serrulatus than to its South American congeners E. pseudoensifer and E. leptacanthus. This species can be easily separated from E. serrulatus and E. pectinifer by the presence of a more complex ornamentation pattern in both the caudal and frontal surfaces of the antennal basis. Eucyclops serrulatus lacks rows N8, N9, N13, N18 and N22 which are present in E. chihuahuensis, and E. pectinifer lacks rows N13, N20 and N22 which are present in E. chihuahuensis. The three abovementioned species share a caudal surface of the P1 coxal sclerite with row I absent and row II bearing long hair-spinules, but differ in the intercoxal ornamentation of P2. In E. pectinifer and E. serrulatus row I on the caudal surface is absent while in E. chihuahuensis it is present and has long hair-spinules; the three species share a row II bearing long hair-spinules. Eucyclops chihuahuensis also differs from E. serrulatus and E. pectinifer in the ornamentation of the P3 intercoxal sclerite. In the first species all rows are armed with long hairs, while in the other two species these rows bear hair-spinules and strong spinules. The P4 intercoxal sclerite also differs among these three species: in E. serrulatus and E. pectinifer row I has long and strong spinules whereas E. chihuahuensis has long hairs.   symmetrical, representing 13.9% of total body length; proximal third of genital double somite expanded laterally. Seminal receptacle with rounded lateral arms on posterior margin. Length/width ratio of caudal rami = 3.7; inner margin of caudal ramus naked, outer margin with strong spines covering 65% with respect to the total length of ramus. Dorsal seta (VII) relatively short: 0.4 times the length of caudal ramus, and 1.1 times as long as outermost caudal seta (III). Ratio of innermost caudal seta (VI)/ outermost caudal seta (III) = 1.3. Lateral caudal seta (II) inserted at 68% of total length of caudal ramus.
Leg 1 (Figure 30A-B). Frontal surface of intercoxal sclerite with row I bearing strong spinules arrenged in semicircular pattern on each side; caudal surface smooth, distal margin with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C. Inner basal seta (basipodal spine) reaching middle margin of Enp3, 0.8 times as long as Enp. Length/width ratio of Enp3 = 1.4, apical spine of Enp3 being 1.1 times as long as Enp3.
Leg 2 ( Figure 30C-F). Frontal surface of intercoxal sclerite with row I bearing small, strong spinules arrenged in a semicircular pattern on each side; caudal surface with row II continuous, with 16 minute spinules, distal margin with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C-D. Small spinules along insertion of basipodite. Length/width ratio of Enp 3 = 2.0, apical spine of Enp3 being 1.2 times as long as Enp3. Modified setae present in Enp and Exp.
Leg 3 ( Figure 30G-I). Frontal surface of intercoxal with row I bearing spinules arranged in semi-circular pattern on each side, proximal spinules longer than the others; caudal surface with row I bearing 13 minute spinules (small gap in the middle), row II continuous, bearing 18 minute spinules; row III with 14 strong, long spinules, with gap in the middle (seven spinules on each side). Distal margin with two rounded projections. Coxa with strong biserially setulated coxal seta, both margins with long setules along proximal section and strong spinules along distal section. Caudal coxal surface with spinule formula = A-B-C. Length/width ratio of Enp3 = 2.2, apical spine of Enp3 being 1.1 times as long as Enp 3. Modified setae in Enp and Exp.
Leg 4 ( Figure 30J-M). Distal margin with two low, rounded, chitinised projections. Frontal surface of intercoxal sclerite with row I bearing minute spinules in semi-circular pattern on each side; caudal surface of intercoxal sclerite with row I bearing nine strong but small spinules on each side, with small gap, row II continuous, bearing 22 spinules, outer spinules slightly longer than inner ones; row III with seven spinules on each side, with wide gap. Frontal surface of coxa with row of small spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; proximal inner margin with long hairs, distal margin with spinules; outer margin with two distal spinules, proximal section with three hairs, gap in middle margin. Caudal coxal surface with spinule formula = A-B-C + D-E-F-H-J. Length/ width ratio Enp3 P4 = 2.5; length ratio inner spine of Enp3 P4/length Enp3 P4 = 1.3; length ratio outer spine of Enp3 P4/length Enp3 P4 = 0.9; proportion inner/outer spine Enp3 = 1.4. Lateral seta of Enp3 inserted at 61% of segment. Modified setae in Enp and Exp.
Leg 5. Free segment subrectangular, 2.2 times longer than wide, bearing one inner spine and two setae; medial and outer setae equal in length. Setae 2.1 times longer than inner spine. Inner spine 1.3 times as long as segment.
Remarks. Eucyclops cuatrocienegas was recognised as a new species by Suárez-Morales and Walsh (2009) based on the peculiarity of its fifth leg, which, diverging from most of its congeners, has a remarkably short inner spine and an outer seta as long as the medial seta. Eucyclops siolii Herbst, 1962 resembles E. cuatrocienegas because of the general shape and armature of the fifth leg, but in E. siolii the outer seta is clearly shorter than the medial seta, and it also has a shorter caudal ramus (2.5 times longer than wide) than that of E. cuatrocienegas (3.7-3.9). It is noteworthy to consider that E. siloii has been recorded only from the Brazilian Amazon. Among the species known from Mexico, only E. pectinifer has a fifth leg resembling that of E. cuatrocienegas. These species can be easily distinguished by the length of the outer and medial setae of the fifth leg; in E. cuatrocienegas these setae are equally long, while in E. pectinifer the medial seta is always longer than the outer seta (about 1.3 times). These two species also share a relatively weak ornamentation of the antennal basis caudal surface when compared with species like E. prionophorus, E. leptacanthus and E. chihuahuensis, bearing rows N20 and N22.

Description
Female. Average length excluding caudal setae = 620 µm. Prosome representing 61% of total body length, symmetrical in dorsal view. Urosomal fringes strongly serrate. Genital double-somite symmetrical ( Figure 31A), carrying paired egg sacs. Seminal receptacle with rounded, lateral arms on posterior margin typical of the serrulatuscomplex. Anal somite with hair-seta in anal opening, anal operculum serrate. Length/ width of caudal ramus = 4.0; inner margin of caudal ramus naked; outer margin with strong spinules covering 40% with respect to the total length of ramus. Dorsal seta (VII) short: 0.65 times the length of caudal ramus, and 1.1 times as long as outermost caudal seta (III). Ratio of innermost caudal seta (VI)/outermost caudal seta (III) = 1.2. Lateral caudal seta (II) inserted at 71% of caudal ramus.
Leg 1 (Figure 32C-D). Frontal surface of intercoxal sclerite with row I bearing spinules arranged in semicircular pattern on each side; caudal surface with row I bearing 17 minute spinules and row II with 14 minute spinules, distal margin with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C. Inner basal seta (basipodal spine) reaching middle margin of Enp3, 0.8 times as long as Enp. Length/width ratio Enp3 = 1.0, apical spine of Enp3 being1.4 times as long as Enp3.
Leg 3 ( Figure 33A-B). Frontal surface of intercoxal sclerite with row I armed with minute spinules arranged in semi-circle on each side; caudal surface with row I bearing long hair-like spinules (small gap in middle section), rows II and III continuous, with minute spinules. Distal margin with two low, rounded projections. Coxa with strong, biserially setulated inner coxal seta, basally with long hairs and distally with strong spinules along both margins. Caudal coxal surface with spinule formula = A-B-C. Length/ width ratio of Enp = 2.2, apical spine of Enp3 being 1.2 times as long as Enp3. Modified setae present in both Enp and Exp.
Leg 4 ( Figure 33C-E). Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface of intercoxal sclerite with row I bearing minute spinules arranged in semicircular pattern; caudal surface of sclerite with row I bearing strong spinules on each side and small gap, row II with small spinules divided into three sections, with small gap between them and row III divided into three sections, first section with five long spinules, middle section with six small, strong spinules, and third section with five long spinules. Inner coxal spine with heteronomous setulation: proximally with long hair-like setules, distally with spinule-like setules; outer edge of coxal spine with three spinule-like setules distally, naked proximally. Caudal surface of coxa with spinule groups A-C + D-E-F-H-J. Length/width ratio Enp3 = 3.0; length ratio inner spine/ length Enp3 = 0.70; length ratio outer spine Enp3/length Enp3 = 1.0; proportion inner/outer spines Enp3 = 1.4. Lateral seta of Enp3 inserted at 66% of segment. Modified setae on Enp3 and Exp3. Leg 5 ( Figure 33F). Free segment subrectangular, 2.1 times longer than wide, bearing one inner spine and two setae; medial seta about 1.3 times longer than outer seta and 1.8 times longer than inner spine. Inner spine 1.7 times as long as segment.
Leg 4. Coxa, Bsp, and intercoxal sclerite as in female, except for distal row of spinules of intercoxal sclerite, which has nine spinules, all longer and more slender than in female. Enp3 P4 being 2.6 times as long as width; inner spines 1.2 times as long as outer spine, and 1.2 times as long as segment. No modified setae on fourth leg. Lateral seta of Enp3 P4 inserted at 64.7% of segment length, lateral seta reaching midlength of outer spine.
Leg 5. Free segment subrectangular, 1.5 times longer than wide, bearing one inner spine and two setae: outer seta about 1.3 times longer than medial seta and 1.3 times longer than inner spine. Inner spine 1.8 times as long as segment.
Leg 6. Represented by small, low plate near lateral margin of genital somite with one strong and long inner spine and two unequal setae. Inner spine reaching distal margin of fourth urosomite. Inner spine about 2.3 times longer than median seta and about 1.6 longer than outer seta.
Remarks. This species, recently described in Gutiérrez-Aguirre et al. (2013), closely resembles Eucyclops bondi. Morphometric values are similar but the lack of data on the ornamentation of the antennal basis of E. bondi did not allow a complete comparison. Other characters that are useful to separate these species include the length of the lateral seta on Enp3 P4, which in E. bondi exceeds half the length of the outer apical spine and is not modified, while in E. tziscao the same seta is shorther, not reaching half the length of the outer apical spine, and it is modified as a strong, heavily sclerotised blunt seta. The male secondary characters have been deemed useful in the separation of species among the Eucyclopinae. Since its original description by Kiefer (1931a), one of the main characteristics of E. bondi (and constantly ignored thereafter in the identification of the species) is the sixth leg of the male, which bears a very small inner spine; it does not reach the posterior margin of the third urosomite and it is smaller than the outer seta and as long as the medial seta. The opposite pattern is present in males of E. tziscao, in which the inner spine is 1.5 times longer than the outer seta and 2.5 longer than the medial seta.
Another species that resembles E. tziscao is E. pectinifer, but strong differences clearly separate these taxa. Among the differences advanced by Gutiérrez-Aguirre et al. (2013) to distinguish these two species, the ornamentation of the anal operculum (smooth in E. pectinifer, serrate in E. tzicao) is one of the strongest. A serrate operculum is shared also with E. elegans and E. defayeae sp. nov. The ornamentation of the antennal basis is simple in both species, but differs mainly by the presence of N18 on the caudal surface and N7, N13 and N14 on the frontal surface of E. pectinifer; these rows are absent in E. tziscao. The ornamentation of the intercoxal sclerites also differs between these two species: E. tziscao is the only species distributed in Mexico in which the sclerite spinules of row I of P1 (frontal surface) are remarkably small, while in the rest of the species these spinules (or in some cases hairs) are always long, conspicuous elements. On the caudal surface of the same P1 sclerite, row I bears minute spinules in E. tziscao but is absent in E. pectinifer. Row II is present in both species but in E. pectinifer it bears long hairs and in E. tziscao it has small spinules. Row I of the P4 intercoxal sclerite has some additional differences; in E. pectinifer this row bears long spinules vs strong and short spinules in E. tziscao. Another species resembing E. tziscao by the presence of modified setae on P3 and P4 and similar length/width proportions of the caudal ramus is E. conrowae. However, they are easily distinguished because E. conrowae is not a member of the serrulatus-groupit lacks groups N1 and N2 on the frontal surface of the antennal basiswhereas in E. tizcao both groups are present in all the specimens examined

Description
Female. Average length excluding caudal setae = 600 µm. Representing 58% of total body length, symmetrical in dorsal view. Prosomal fringes serrate dorsally; fourth pediger with long, lateral, hair-like setae. First urosomite with long spinules on lateral margin; urosomal fringes strongly serrate. Posterior margin of anal somite with large spinules on ventral and dorsal surfaces, except for the medial section. Genital double somite symmetrical, lateral arms of proximal part of seminal receptacle rounded; distal section forming sinuous sac. Anal somite subequal in length to preanal somite, with hairlike setae adjacent to anal pore. Length/width of caudal ramus = 2.1; inner margin of caudal ramus naked, strong spines covering 62% with respect to the total length of ramus. Dorsal seta (VII) 0.8 times as long as caudal ramus, and 1.1 times as long as outermost terminal caudal seta (III). Ratio of innermost caudal seta (VI)/outermost caudal seta (III) = 1.5. Lateral caudal seta (II) inserted at 71.6% of caudal ramus.
Leg 1. Frontal surface of intercoxal sclerite with row I bearing long spinules arranged in semicircular pattern, caudal surface with row II bearing 21 small, strong spinules, row I absent. Inner coxal seta biserially setulated, caudal surface with spinule formula = A-C. Inner basal seta (basipodal spine) reaching beyond apical margin of Enp3, 0.9 times as long as Enp. Length/width ratio Enp3 = 1.4, apical spine of Enp3 being 1.3 times as long as Enp3.
Leg 2. Frontal surface of intercoxal sclerite with row I bearing long hair-spinules arranged in circular pattern; caudal surface with row I divided in two groups of 10 minute spinules on each side; row II continuous, armed with 10 minute spinules. Distal margin of intercoxal sclerite with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C-D. Length/width ratio Enp3 = 1.6, apical spine of Enp3 being 1.4 times as long as Enp3. No modified setae observed.
Leg 3. Frontal surface of intercoxal sclerite with row I bearing hair-spinules arranged in circular pattern on each side; caudal surface with row I bearing long hairs (small gap in middle section), row II continuous, bearing long hair-spinules; row III discontinuous, with long hair-spinules (small gap in middle section). Distal margin with two rounded, chitinised projections. Coxa with strong, biserially setulated inner coxal seta, basally with long hairs and distally with strong spinules along both margins. Caudal coxal surface with spinule formula = A-B-C. Modified setae in both Enp and Exp.
Leg 4. Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface with row I bearing long spinules arranged in circular pattern (on each side), caudal surface of sclerite with row I bearing seven long denticles (gap in middle section), rows II and III with long hair-spinules on outer margins. Frontal coxal surface with row of small spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; basally, inner margin with long hairs; distally, with strong spinules. Outer distal margin naked, proximal section setulated. Spinule formula on caudal surface of coxa = A-B-C + D-E-F-G-H-J. Length/width ratio Enp3 = 1.8; length ratio inner spine of Enp3/length Enp3 = 1.3; length ratio outer spine of Enp3/length Enp3 = 0.9; length ratio inner/outer spines Enp3 = 1.3. Lateral seta of Enp3 inserted at 68% of segment. Modified setae present in both, Enp and Exp.
Leg 5. Free segment 1.4 times longer than wide, bearing one inner spine and two setae; medial seta 2.0 times longer than outer seta and 1.3 times longer than inner spine. Inner spine twice as long as segment.
Leg 5. Free segment 1.6 times longer than wide, bearing three elements; outer seta slightly longer than in female (subequal in length to inner spine). Inner spine 1.8 times as long as segment.
Leg 6. Represented by small, low plate adjacent to lateral margin of genital somite, armed with one inner spine, 1.87 times longer than median seta, and 0.6 times longer than outer seta. Inner spine of sixth leg reaching distal margin of fourth urosomite.
Remarks. Eucyclops angeli is easily distinguishable from the other species of Eucyclops distributed in Mexico because of its remarkably short caudal rami and the unique ornamentation on the P4 coxa. There are other species in the Americas that share with E. angeli short caudal rami such as E. breviramatus and E. siolii, but these species are restricted to South America. As mentioned by Gutiérrez-Aguirre et al. (2013), Löffler's description of E. breviramatus did not include the new, currently used characters, but some other characters are useful to distinguish them. The length/width ratio of Enp3 P4 differs between these species; in E. angeli the ratio range is 1.8-2.0 while in E. breviramatus the segment is shorter (1.4-1.5). Another character that could be useful to separate these species is the armature of the male sixth leg; in E. angeli the inner spine is almost twice as long as the medial and outer setae, while in E. breviramatus the inner spine is clearly shorter, only 1.2 times longer than both the outer and medial setae. Eucyclops angeli can be distinguished from E. siolii by the shape and size of P5; in both species the medial seta is longer than the outer seta and the inner spine but in E. siolii the inner spine is remarkably short, being as long as or slightly shorther than the segment. Other species resembling E. angeli but from other geographic regions are the recently described E. albuferensis from Spain (Alekseev 2008 Figure 36B), representing 11% of total body length; widest proximally, tapering towards distal edege. Seminal receptacle with rounded lateral arms; posterior margin with sinuous sac ( Figure 34A). Anal operculum slightly rounded, smooth ( Figure 34B). Length/width of caudal ramus = 3.5; inner margin of caudal ramus naked; strong spinules covering 60% with respect to the total length of ramus. Dorsal seta (VII) 0.5 times as long as caudal ramus, 0.8 times as long as outermost caudal seta (III). Ratio of innermost caudal seta (VI)/outermost caudal seta (III) = 1.3. Lateral caudal seta (II) inserted at 73% of caudal ramus.
Leg 2 ( Figure 35B-D, 38C-D). Frontal surface of intercoxal sclerite with row I bearing long hair-spinules arranged in a semicircular pattern; caudal surface with row II continuous, bearing 17 small spinules, row I absent. Distal margin of intercoxal sclerite with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C-D. Length/width ratio of Enp3 = 2.0, apical spine of Enp3 1.4 times as long as Enp3. No modified setae present.   Leg 4 ( Figures 35G-H, 39C-E). Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface of sclerite with row I bearing small spinules arranged in a semicircular pattern, caudal surface with row I bearing long, strong spinules (gap in the middle margin), row II with strong spinules on each side of sclerite and row III with long, strong spinules on outer margins. Frontal surface of coxa with row of small spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; proximal inner margin with long hairs, distal margin with strong spinules, outer margin with three spinules on distal surface and proximally smooth. Spinule formula on caudal surface = A-B-C + D-E-F-H-J. Length/width ratio Enp3 = 2.6, length ratio inner spine of Enp3/length Enp3 = 1.2; length ratio outer spine of Enp3/length Enp3 = 0.9; proportion inner/outer spines Enp3 = 1.4. Lateral seta of Enp3 inserted at 67% of segment. Modified setae in Enp and Exp.
Leg 5 ( Figure 39F). Free segment subrectangular, 1.5 times longer than wide, bearing one strong inner spine and two setae; medial seta 1.5 times longer than outer seta and 1.8 times longer than inner spine. Inner spine 2.0 times longer than segment. Male. Prosome symmetrical in dorsal view. Urosome slightly elongated. Caudal ramus smooth along both inner and outer margins, except for strong spinules at insertion of lateral seta. Length/width ratio of caudal ramus = 2.7, dorsal seta (VII) 0.8 times as long as caudal ramus and 1.3 times as long as outermost caudal seta (III). Innermost caudal seta (VI)/outermost caudal seta (III) ratio = 2.2. Lateral caudal seta (II) inserted at 72% of ramus length.
Legs 1-4. Enp and Exp of all swimming legs three-segmented, armed as in females.
Leg 5. Free segment subrectangular, 1.7 times longer than wide, bearing inner spine and two setae; medial seta longer than outer seta (about 1.3 times) and inner spine (1.3 times). Inner spine as long as outer seta.
Leg 6. Represented by small, low plate adjacent to lateral margin of genital somite, armed with one strong inner spine and two unequal setae. Inner spine reaching medial margin of fourth urosomite, inner spine 1.8 times longer than medial seta and 1.5 times longer than outer seta. Small, strong spinules present at insertion of inner spine.
Remarks. Eucyclops alekseevi sp. nov. belongs to the serrulatus-group because it has the diagnostic characters established by Alekseev and Defaye (2011) to recognise members of this group: (1) longitudinal row of spinules along most of the outer margin of caudal ramus and without hair-like setae or denticles on dorsal or ventral surfaces; (2) antennules 12-segmented, with smooth membrane along three distal segments; (3) frontal side of antennal basipodite with groups N1 and N2 (both with long hairs or spinules); (4) coxopodite of P4 with strong inner spine; and (5)

Etymology
This species is warmly dedicated to one of the most important indigenous ethnic groups from Mexico, the Wixaricas or Huicholes. One of their main ceremonial sites is located in the state of San Luis Potosí, where the type specimens were collected.
Leg 2 ( Figures 41C-D, 44D-E). Frontal surface of intercoxal sclerite with row I bearing hairs arranged in circular pattern; caudal surface with row I divided into two groups bearing long hairs and arranged in a semicircular pattern on each side and close to the posterior margin. Row II continuous, with small hairs. Distal margin of intercoxal sclerite with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal Leg 3 (Figures 41E-G, 44F, 45A). Frontal surface of intercoxal sclerite with hairs arranged in circular pattern on each side; caudal surface with row I bearing long hairs (gap in the middle section), rows II and III continuous, bearing long hairs. Distal margin with two rounded, chitinised projections. Coxa with strong, biserially setulated inner coxal seta, proximally with long hairs and distally with strong spinules along both margins. Caudal coxal surface with spinule formula = A-B-C. Length/width ratio of Enp = 2.2, apical spine of Enp3 being 1.2 times as long as Enp3. No modified setae present.
Leg 4 ( Figures 41H-I, 45B-F). Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface of sclerite with row I bearing long hairs arranged in circle, caudal surface of intercoxal sclerite with row I bearing very long hairs, row II with long hairs on outer margins; row III with long hairs close to outer margins. Frontal surface of coxa with row of small spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; inner margin with long hairs on proximal section and with strong spinules distally; outer margin with one distal spinule and setulated along proximal section, gap in middle margin. Spinule formula on caudal surface = A-B-C + D-E-F-H-J. Length/width ratio Enp3 = 2.5, length ratio inner spine of Enp3/length Enp3 = 1.3; length ratio outer spine of Enp3/length Enp3 = 0.9; length ratio inner/outer spines Enp3 = 1.5. Lateral seta of Enp3 inserted at 65% of segment. No modified setae in Enp and Exp.
Leg 5. Free segment subrectangular, 1.4 times longer than wide, bearing one strong inner spine and two setae; medial seta 2.4 times longer than outer seta and 1.5 times longer than inner spine. Inner spine 2.6 times longer than segment.
Legs 1-4. Enp and Exp of all swimming legs three-segmented, armed as in females.
Leg 6 ( Figure 43B). Represented by small, low plate adjacent to lateral margin of genital somite armed with strong inner spine and two unequal setae. Inner spine reaching posterior margin of third urosomite, inner spine 1.5 times longer than medial seta and 1.6 longer than outer seta. Strong spinules at insertion of inner spine.
Remarks. Eucyclops wixarica sp. nov. can be easily distinguished from most of its congeners distributed in the Americas by the presence of long hair-like elements on the frontal surface of the antennal basipodite; this character is shared with the American E. elegans, E. defayeae sp. nov. and E. mittmanni sp. nov., and also with some other members of the serrulatus-group such as E. serrulatus s. str., E. romaniensis, E. albuferensis, E. miracleae, E. agiloides roseus, E. pacificus and E. vandouwei; these species are known from Europe, Africa and Asia (Ishida 2000;Dussart and Defaye 2006;Alekseev 2008Alekseev , 2010Alekseev and Defaye 2011). Eucyclops wixarica sp. nov. differs from E. elegans and E. mittmanni sp. nov. because of its total body length. The two latter species aretogether with E. neumani s. str. and E. titicacaethe largest Eucyclops in the Americas; their size is > 1050 µm, whereas E. wixarica sp. nov. is clearly a smaller species (810 µm). Also, the new species can be distinguished from those species by the length/width ratio of the caudal ramus; it is about 5.1 in the new species vs more than 6.0 in both E. elegans and E. mittmanni sp. nov. The ornamentation of the antennal basis is more complex in E. elegans and E. mittmanni sp. nov. than in E. wixarica sp. nov. In addition, the caudal surface of the P3 and P4 coxal plates differs among these species. In E. wixarica all rows of both P3 and P4 are long hairs, whereas some rows with spinules are present in the other species. Eucyclops wixarica sp. nov. seems to be closely related to E. serrulatus because of the presence of long hairs on row N2 of the antennal basis and the similar length/width ratio of the caudal ramus (about 5.0 in both species), and also in most morphometric values. These species can be separated by a combination of characters. Row N6 is absent in E. wixarica sp. nov. and is present in E. serrulatus. The new species shows a more complex ornamentation on the caudal surface of the antennal Bsp; it has rows N8, N10, N13, N16 and N18, all of them absent in E. serrulatus. The ornamentation of the caudal surface of P2 intercoxal sclerite diverges in these species; in E. wixarica sp. nov. row I is present but it is absent in E. serrulatus. Also, the P3 and P4 sclerites have rows with strong spinules in E. serrulatus, thus differing from E. wirxarica sp. nov., in which all rows bear long hair-like elements. The P4 coxa of E. wixarica sp. nov. has row F; this row is absent in E. serrulatus.

Etymology
This species is warmly dedicated to Dr. Danielle Defaye (Museum National d'Histoire Naturelle, Paris) for her many contributions to the knowledge of the taxonomy and systematics of freshwater copepods, and also for all her kind help and advice during the development of this work.

Distribution
Central and Northern part of Mexico (Aguascalientes, Zacatecas, San Luis Potosí).
Leg 1 (Figures 49A-C, 51F, 52A). Frontal surface of intercoxal sclerite smooth (rows not observed), caudal surface with row II continuous, bearing 21 strong but small spinules, row I absent. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C. Inner basal seta (basipodal spine) long exceeding apical margin of Enp3, 1.1 times as long as Enp. Length/width ratio Enp3 = 1.2, apical spine of Enp3 being 1.1 times as long as Enp3. Leg 2 ( Figure 49D-G). Frontal surface of intercoxal sclerite with row I bearing strong spinules arranged in a semicircular pattern; caudal surface with rows I and II continuous, row I with 14 minute spinules and row II with 23. Distal margin of intercoxal sclerite with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule formula = A-B-C-D. Length/width ratio of Enp3 = 1.7, apical spine of Enp3 being 1.1 times as long as Enp3. No modified setae present.
Leg 3 (Figures 49H, 52B-C). Frontal surface of intercoxal sclerite with minute spinules arranged in a semicircular pattern on each side; caudal surface with row I bearing small, strong spinules (gap in middle section), row II continuous, bearing small, slender spinules; row III continuous, with strong, long spinules (spinules adjacent to outer margins longer than those in middle section). Distal margin with two rounded, chitinised projections. Coxa with strong, biserially setulated inner coxal seta, basally with long hairs and distally with strong spinules along both margins. Caudal coxal surface with spinule formula = A. Length/width ratio of Enp = 2.0, apical spine of Enp3 being 1.1 times as long as Enp3. Modified setae present in Exp and Enp. Leg 4 ( Figures 49I-J, 52D-F, 53A). Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface of sclerite with row I bearing minute spinules arranged in a semicircular pattern, caudal surface of sclerite with row I bearing long, strong spinules, row II continuous, with small spinules; row III with strong, slightly longer spinules, small gap in middle section. Frontal surface of coxa with row of small spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; proximal inner margin with long hairs, distal margin with strong spinules, outer margin with two distal spinules, proximally setulated, gap in middle margin. Spinule formula on caudal surface = A-B-C + D-E-F-H-J. Length/width ratio Enp3 = 2.4, length ratio inner spine of Enp3/length Enp3 = 1.2; length ratio outer spine of Enp3/length Enp3 = 0.7; length ratio inner/outer spines Enp3 = 1.8. Lateral seta of Enp3 inserted at 64% of segment. Modified setae in Enp and Exp.
Leg 5 (Figures 48B, 53B). Free segment subrectangular, 1.8 times longer than wide, bearing one strong inner spine and two setae; medial seta 1.8 times longer than outer seta and 2.3 times longer than inner spine. Inner spine 1.4 times longer than segment.
Remarks. As mentioned in the remarks section of other species, E. defayeae sp. nov.
shares with E. elegans and E. tziscao some characters like the rounded, serrate anal operculum, but differs from E. elegans in the body length and the length/width ratio of the caudal ramus; in this new species the ramus is 4.6 times longer than wide, vs a ratio of over 6.0 found in E. elegans. This new species can be easily distinguished from E. tziscao by the ornamentarion of the frontal surface of the antennal basis: row II bears long hairs in E. defayeae sp. nov., but in E. tziscao it has small, strong spinules. Mexican records of E. bondi are now assignable to either E. tziscao or E. defayeae sp. nov. These three species share general morphometric values and the same armature of the caudal surface of the intercoxal sclerite of P4. Both Mexican species can be easily distinguished from E. bondi if males are available. The sixth leg in E. bondi differs from that of E. tziscao and E. defayeae sp. nov. in having a remarkably short inner spine and a medial seta as long as or slightly longer than the spine, and an outer seta longer than the inner spine. In both E. tziscao and E. defayeae sp. nov., the inner spine is always much longer than both the medial and the outer setae. Eucyclops tziscao and E. defayeae sp. nov. can be distinguished because in the former species the frontal surface of the antennal basis row N2 bears short spinules vs long hairs in E. defayeae sp. nov. Rows N6, N7, N14, N16 and N18 are present in E. defayeae sp. nov. but they are absent in E. tziscao (Gutiérrez-Aguirre et al. 2013). The ornamentation on the caudal surface of P1 and P2 intercoxal sclerites differs between these species: in E. defayeae sp. nov. row I of P1 is absent but it is present in E. tziscao, and row I of P2 is present in E. defayeae sp. nov. but it is absent in E. tziscao. The presence of caudal spinules on P3 row I is another distinctive character in E. defayeae sp. nov. Among the species distributed in Mexico, this character is shared with E. cuatrocienegas and E. mittmanni sp. nov.
The only other known congener sharing the presence of long hairs in row N2 with E. defayeae sp. nov. is E. wixarica, but N6 is absent in E. wixarica sp. nov.; in addition, rows N9 and N10 are separated in E. wixarica sp. nov. but fused in E. defayeae sp. nov. Additional differences between these two species include the ornamentation of the caudal surface of the P1 intercoxal sclerite: row I is present and bears minute spinules in E. wixarica but it is absent in E. defayeae sp. nov. The ratio of basipodal spine/length of Enp of P1 is 0.6 in E. wixarica, while in E. defayeae sp. nov. the spine is remarkably long (about 1.1). Also, modified setae were observed in P3 and P4 of E. defayeae sp. nov., while in E. wixarica all swimming setae are normal.

Type locality
Creek at Sierra Fria 21 km north of Village La Labor, Calvillo, Aguascalientes, Mexico.

Etymology
This species is warmly dedicated to Dr. Hans-Walter Mittmann (Staatliches Museum für Naturkunde Karlsruhe, Germany) who is in charge of the Kiefer Collection.

Description
Female. Habitus as in Figure 57A. Average length excluding caudal setae = 1216 µm. Whole body (caudal ramus included) ornamented with small cuticular pits. Prosome representing 58% of total body length, symmetrical in dorsal view. Prosomal fringes finely serrate dorsally. Urosomal fringes strongly serrate. Genital double somite symmetrical ( Figure 57B), representing 10% of total body length; proximal third of genital double somite slightly expanded laterally. Seminal receptacle with rounded lateral arms on posterior margin, typical of the serrulatus-complex. Length/ratio of caudal ramus = 7.5; inner margin of caudal ramus naked; strong spines covering 69% with respect to the total length of ramus. Dorsal seta (VII) 0.5 times as long as caudal ramus and 0.8 times as long as outermost caudal seta (III). Ratio of innermost caudal seta (VI)/ outermost caudal seta (III) = 0.8. Lateral caudal seta (II) inserted at 78% of caudal ramus.
Leg 2 ( Figures 56C-D, 59C). Frontal surface of intercoxal sclerite with row I bearing spinules arranged in circular pattern on each side; caudal surface with row II continuous, with 20 minute spinules, row I absent, distal margin with two rounded, chitinised projections. Inner coxal seta biserially setulated, caudal coxal surface with spinule with 25-28 long spinules, spinules adjacent to outer margin longer than medial ones. Distal margin with two rounded, chitinised projections. Coxa with strong, biserially setulated coxal seta, ornamented basally with long hairs and distally with strong spinules. Caudal coxal surface with spinule formula = A-B-C. Length/width ratio of Enp3 = 2.7, apical spine of Enp3 as long as segment (Enp3). No modified setae present.
Leg 4 ( Figures 56G-H, 59C-E). Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface with row I bearing long hairs arranged in semicircular pattern; caudal surface of intercoxal sclerite with row I bearing 10-11 strong long spinules on each side with small gap between, row II discontinuous, with long hair spinules adjacent to outer margins and three strong, long spinules in middle section. Row III with long hair-spinules in outer margins. Frontal surface of coxa with spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; proximal inner margin with long hairs, distally with spinules; outer margin with three spinules on distal surface and basally with hairs, gap in middle margin. Caudal coxal surface with spinule formula = A-B-C + D-E-F-H-J. Length/width ratio Enp3 P4 = 3.7, length ratio inner spine of Enp3/length Enp3 = 1.0; length ratio outer spine of Enp3/ length Enp 3 = 0.8; length ratio inner/outer spines Enp3 = 1.3. Lateral seta of Enp3 inserted at 62% of segment. No modified setae in Enp and Exp.
Leg 5 (Figures 59F, 60F). Free segment subrectangular, 1.6 times longer than wide, bearing one inner spine and two setae; medial seta 1.6 times longer than outer seta and 1.1 times longer than inner spine. Inner spine 2.7 times longer than segment.
Remarks. Eucyclops mittmanni sp. nov. is closely related to E. elegans; it is possible that some Mexican and North American records of the latter species are now assignable to E. mittmanni sp. nov. Most of the records of E. elegans (Suárez-Morales, 2004) have been based upon the length of its caudal ramus, which is remarkably longer than that of closely related species like E. pectinifer and E. serrulatus. This apparently unique character might have prevented further analysis of specimens from different geographic areas or Mexico. In the recent redescription of E. elegans (Mercado-Salas and Suárez-Morales, 2014b) from material deposited in different collections and including specimens from different geographic areas of the continent, differences were found between North American (NA) and South American (SA) populations of this species. It is suggested that the NA and SA specimens could represent two independent species. Eucyclops mittmanni sp. nov. differs from both forms of E. elegans by a combination of different characters, but, as expected, it appears to be more closely related to the NA form of E. elegans. Morphometrical values do not differ among these species, but it is important to mention that E. elegans NA (body length = 1061 µm) and E. elegans SA (1100 µm) are both slightly smaller than E. mittmanni sp. nov. (1216 µm). The new species shares with the SA populations a round and smooth anal operculum; the same structure is also rounded but serrate in the NA form. Some of the main differences observed between both the SA and NA forms of E. elegans and E. mittmanni sp. nov. are related to the ornamentation pattern of the antennal basis. In the three forms the frontal surface has the same pattern except for E. elegans NA, which shows N18, and in E. mittmanni sp. nov. N1 and N2 are completely separated, thus contrasting with the fused condition observed in the two forms of E. elegans. The ornamentation pattern on the caudal surface also differs among both forms of E. elegans and E. mittmanni sp. nov.: in E. elegans SA rows N7, N14, N22 are absent, while in E. elegans NA and E. mittmanni sp. nov. they are present. Like many other Mexican congeners, E. elegans NA bears row N18, a character that is absent in E. mittmanni sp. nov. The new species is the only one among the Mexican Eucyclops that has rows N19 and N20; it shares the presence of N20 with E. chihuahuensis only. The ornamentation of P1 and P2 intercoxal sclerites is similar in the three forms but some differences were observed in the P3 caudal surface. In E. elegans NA row I bears long hair-spinules, a character shared with other Mexican species of Eucyclops, but divergent from both E. mittmanni sp. nov. and E. elegans SA in which row I has small strong spinules, also present in E. defayeae sp. nov. and E. cuatrocienegas. In the new species, row III has remarkably long, strong spinules that are shorther in E. elegans NA. The ornamentation of the caudal surface of the P4 coxa and intercoxal sclerite is another useful character to separate the three forms: in E. mittmanni sp. nov. and E. elegans SA row II is divided into three sections, two close to the outer margins and one bearing long spinules in the middle section, whereas this row is continuous and bears small but strong spinules in E. elegans NA. The coxal surface of P4 is more ornamented in the new species than in the two forms of E. elegans, and rows B, C and E are present in E. mittmanni sp. nov. and are absent in E. elegans, but E. elegans has row G, absent in the new species.

Etymology
This species is warmly dedicated to the late Mrs. Esther Ruiz Jiménez, the beloved grandmother of the first author (NFM-S).
Leg 5 ( Figure 66F). Free segment subrectangular, 1.5 times longer than wide, bearing one strong inner spine and two setae; medial seta 3 times longer than outer seta and 1.4 times longer than inner spine. Inner spine 2.5 times longer than segment.
Legs 1-4. Enp and Exp of all swimming legs three-segmented, armed as in females.
Leg 5. Free segment subrectangular, 2.1 times longer than wide, bearing one inner spine and two setae, medial seta longer than inner spine and outer seta (about 1.2 times), inner spine and outer seta equal in size.

Leg 6.
Represented by a small, low plate adjacent to lateral margin of genital somite, armed with one strong spine and two unequal setae. Inner spine reaching posterior margin of fourth urosomite, inner spine 1.8 times longer than medial seta and 2.2 times as long as outer seta. Small and strong spinules presents at insertion of inner spine.

Type locality
Creek at Sierra Fria, 21 km from La Labor, Calvillo, Aguascalientes, Mexico.

Etymology
This species is dedicated to Dr. Teruo Ishida, who pioneered the exploration of new morphological characters to distinguish closely related species of Eucyclops.

Description
Female. Habitus as in Figure 69A. Average length excluding caudal setae = 788 µm. Body surface (including caudal rami) ornamented with small pits. Prosome widest at end of cephalosome and second pediger, representing 62% of total body length, symmetrical in dorsal view. Prosomal fringes finely serrate in dorsal surface. Five-segmented urosome, slightly elongated; first urosomite with long setules on lateral margin; urosomal fringes serrate dorsally and ventrally; posterior margin of anal somite with row of strong spinules. Genital double somite symmetrical ( Figure 69B), representing 13.4% of total body length; anterior half of genital somite slightly expanded. Seminal receptacle with rounded, slender lateral arms on posterior margin, typical of the serrulatus-complex. Anal somite subequal in length to preanal somite, anal operculum rounded ( Figures  67G, 69D). Length/width of caudal ramus = 4.1; inner margin of caudal rami naked; strong spinules covering 64% of total length of ramus. Dorsal seta (VII) 0.8 times as long as caudal ramus and 1.2 times as long as outermost caudal seta (III). Length ratio of innermost caudal seta (VI)/outermost caudal seta (III) = 1.5. Lateral caudal seta (II) inserted at 76% of caudal ramus. All terminal setae plumose.
Leg 2 ( Figures 68B-C Leg 4 ( Figures 68G, 72C-E). Distal margin of intercoxal sclerite with two low, rounded, chitinised projections. Frontal surface of sclerite with row I bearing hairs arranged in semicircular pattern in both sides of surface. Caudal row I with seven long and slender spinules on each side and a small gap in the middle, row II bearing very long spinules, divided into three sections: two on outer margins and one medial; row III bearing long, slender spinules, also divided into three sections, two on outer margins and one in medial margin. Frontal surface of coxa with row of small spinules at insertion of Bsp. Inner coxal spine with heterogeneous ornamentation; proximal inner margin with long hairs and with strong spinules distally, outer margin with one distal spinule basally setulated, gap in middle margin. Caudal coxal surface with spinule formula = A-C + D-E-F-H-J. Length/width ratio of Enp3 = 3.1, inner spine of Enp3 as long as Enp3 (1.0), length ratio of outer spine of Enp3/length Enp3 = 0.7; length ratio inner/outer spines of Enp3 = 1.4. Lateral seta of Enp3 inserted at 67% of segment. No modified setae observed.
Leg 5 ( Figure 72F). Free segment subrectangular, 1.1 times as long as wide, bearing one strong inner spine and two setae, medial seta 1.7 times longer than outer seta and 1.6 times longer than inner spine. Inner spine 2.3 times longer than segment.

Male. Unknown.
Remarks. Records of E. ishidai sp. nov. were previously assigned to E. pectinifer (Mercado-Salas and Suárez-Morales, 2012); however, significant differences were found among these closely related species.

Morphometrics and binary characters
In order to test the taxonomic value of the morphometric variables traditionally used in the separation of the species (Lindberg 1955;Reid 1985; Suárez-Morales 2004; Alekseev and Defaye 2011) we performed a statistical analysis using boxplots with the aid of the statistical program R 3.0.2. (R Development Core Team 2008). We included 22 morphometrical characters measured in the 17 species included herein. We observed (Figure 73) a lack of significant variation and a remarkable overlap of data in the morphometric characters used in the separation of species of the genus. The only characters that appear to have a consistent variation among species and that could be deemed useful in the separation of species are the length/width ratio of the caudal ramus (2), the length/ width ratio of P4 Enp3 (14) and the spine and setae proportions of the fifth leg armature (19-22), but even in these characters, variation is relatively weak, so they should not be used as defining characters. The cluster analysis was performed using Euclidean distance in order to classify and verify dissimilarities among species in relation to the shared characters ( Figure 73). It included all characters (morphometric and binary) examined. The cluster in Figure 73B shows the results obtained using morphometrical data only.

Discussion
After performing this upgraded taxonomic analysis of the Mexican fauna of Eucyclops, we have evidence to state that all the species known to be distributed in Mexico belong to the serrulatus-group, based on the diagnostic characters established by Alekseev and Defaye (2011). Additional to these basic characters, we found wellconserved patterns in the ornamentation of the swimming legs that could be a reliable tool to distinguish even closely related species. In one of the few studies that explore the taxonomic value of the ornamentation patterns of all the swimming legs, Einsle (1985) emphasised the uniformity of such patterns within species and outlined their remarkable interspecific variations. Furthermore, Einsle (1985) stressed the taxonomic importance of the presence of rows rather than the number of elements in each row, which often varies among individuals. Our observations support these statements; in addition, the type of elements in each row is constant within species and varies among species. We consider the type of elements the presence of hairs, hair-spinules and spinules. Based on our analysis, we can advance the following micro-characters as the most stable and reliable in Eucyclops: (1) coxal formula A-B-C on the caudal surface of P1; (2) frontal row I of the P1 intercoxal sclerite; (3) caudal row II of intercoxal sclerite (P1), its position always at the same level of row C of coxa, and the presence or absence of row I; (4) coxal formula A-B-C-D on the caudal surface of P2; (5) row I of the frontal surface of P2 always close to round, chitinised projections; (6) caudal row II always present at the same level as row D of the coxal surface and, in some species, an additional row I above row II; (7) coxal formula A-B-C on the caudal surface of P3, (8) row I of the frontal surface of the intercoxal sclerite of P3 close to round, chitinised projections; (9) caudal surface of the intercoxal sclerite of P3 with three rows, the first (row I) close to the proximal margin, the second (row II) below the first and the third at the same level as row C of the coxal surface; (10) caudal surface of the coxa in P4 as described by Alekseev and Defaye (2011); (11) row I of the frontal surface of the intercoxal sclerite P4; (12) caudal surface with pattern as described by Alekseev and Defaye (2011) with rows I, II and III. With the exception of caudal row I of the intercoxal sclerite of P1 and P2, these characters are always present in Eucyclops but the type of ornamentation elements varies among species. Previous surveys on the ornamentation patterns of coxae and intercoxal sclerites have been performed analysing the fourth leg and the P1 of some genera (Karaytug 1999). This is the first time that ornamentation patterns of all swimming legs (P1-P4) are analysed and compared. Based on the ornamentation of P4, Hołyńska (2000) recognised different linages in Mesocyclops that were geographically consistent; she also outlined the relevance of these patterns as signals of evolution in copepods. According to Huys and Boxshall (1991), Karaytug and Boxshall (1999) and Hołyńska (2000), the ornamentational patterns in the coxal plate of the fourth swimming leg could represent a key character in the recognition between males and females of the same species, because the male antennules and the female coxae are in contact during mating. This might be true in Eucyclops; this ornamentation pattern could be a key factor in intraspecific sexual recognition. Additional observations of the Mexican material revealed that when caudal row III of the P4 intercoxal sclerite is armed with hairs (always long), the three caudal rows of P3 will have hairs too; also, when caudal row I of P4 bears spinules (small or long), at least two of the three rows present at the caudal surface of the intercoxal sclerite of P3 will bear spinules as well. The only species with long hairs in caudal row I of P4 are E. wixarica, E. defayeae and E. chihuahuensis. In the taxonomic literature on American species of Eucyclops, the ornamentation elements of several species have been described as bearing long hair-spinules on this row, but we consider that some of them refer to long spinules and that should be analysed in order to determine if this pattern is constant among species.
Most of the species distributed in Mexicowith the exception of E. mittmanni and E. tziscaohave row N18 on the frontal surface of the antennal basis. This structure should be reviewed in the rest of the American Eucyclops because it could represent a character with the potential to separate Neartic/Neotropical species from those of Palearctic origin (in E. serrulatus this row is absent, as it is in many European, African and Asian species; Ishida 1997Ishida , 2001Ishida , 2002Ishida , 2003Alekseev et al. 2006;Alekseev 2008Alekseev , 2010Alekseev and Defaye 2011). Our analysis of the ornamentation patterns of the antennal basis allowed us to add rows of spinules to the pattern proposed by Alekseev et al. (2006) and Alekseev and Defaye (2011). Some of the Mexican specimens examined have additional rows that do not fit in the previously described patterns and, thus, were important to identify groups of species.
The use of morphometric characters in the delimitation of species of Eucyclops has been proven to have a limited taxonomic value, and has led to underestimation of the biodiversity of the genus not only in Mexico but on the entire continent. Many species have been recorded under names of presumedly 'cosmopolitan' species such as E. elegans, E. pectinifer, E. bondi and E. pseudoensifer. The examination of the ornamentational patterns present in the four swimming legs and the antennal basis is here advanced as a more reliable set of data to achieve more accurate species delimitation on the continent. In addition, frequently ignored male-related characters such as (1) the presence of modified setae on the antennule and (2) the shape of the sixth leg are deemed useful when differences in females are subtle. An example of this situation is represented by records of E. bondi; since its description (Kiefer 1934) it has been recorded in Central America, the Antilles and Mexico by several authors (Collado et al. Sinaloa and Sonora. Thus, it is probable that the Sierra Madre Occidental mountain belt and the Gulf of California represent a geographic barrier limiting the distribution of Eucyclops in Mexico; it is necessary to obtain more samples from this area in the country to confirm this assumption. We performed an analysis of variables using boxplots in order to graphically analyse the variability of the characters examined. We emphasised the evaluation of morphometrical characters traditionally used in the separation of species of Eucyclops. Most of the characters have weak variations and thus are not informative in species delimitation; extreme values ( Figure 74) were obtained in some morphometric characters, like the total length of the caudal ramus. The species that represent these extreme values were E. mittmanni sp. nov., E. elegans and E.angeli, the first two species with remarkably long caudal rami and the third with very short caudal rami. Differences between the cluster obtained using morphometric characters and that incorporating both binary and morphometric characters are important to highlight, but the groups obtained are not geographically consistent. One of the explanations for this is the lack of material from larger geographical areas in Mexico which may contain forms that could be used in searching biotic components. It is also important to mention that all species (in both clusters) appear as independent entities, suggesting that the new species described herein are well supported and that it is possible to separate them from their congeners. The cluster with all characters (morphometric and binary) provided a clearer separation among species, thus supporting the idea that the use of ornamentational patterns is an important tool to species delimitation in the genus.
It is also clear that the diversity of the genus in Mexico was underestimated; prior to this survey, the number of species of Eucyclops in Mexico was 16 (including E. agilis, E. serrulatus and E. speratus); however, records of E. breviramatus, E. bondi, E. conrowae, E. delachauxi, E. speratus and E. pseudoensifer were determined incorrectly, and thus these species are not distributed in the country. The addition of eight new species and the confirmation of nine species previously recorded in Mexico resulted in an updated figure of 17 species dwelling in the country. Future taxonomic works in areas of Mexico that are currently unknown or subsampled are expected to reveal more undescribed species. 13. Caudal surface of intercoxal sclerite of P3 with row I bearing long hairs. Coxa of P4 with row J divided into three sections with small spinules ( Figure 27J); anal operculum smooth and rounded but with small gap at middle section ( Figure 27A)