(Figure 2).

Palaemon jelskii Miers, 1877: 661, plate LXVII, fig. 1.

Bithynis jelskii — Young, 1900: 489.

Macrobrachium amazonicus — Schmitt, 1936: 373.

Macrobrachium jelskii — Chace & Holthuis, 1948: 23;— Holthuis, 1950: 30;— Holthuis, 1952: 26, Pl. 4, fig. a – d;—Chace & Hobbs, 1969: 109, Fig. 25;— Kensley & Walker, 1982: 9, Fig. 10;— Rodríguez, 1982: 386;— Barros & Braun, 1997: 15;— Ramos-Porto & Coelho, 1998: 334;— Collins, 2000: 1167, Fig. 1;— García-Dávila & Magalhães, 2003: 672, Fig. 18 – 20;— Melo, 2003: 362, Fig. 207;— Magalhães et al., 2005: 1934;— Almeida et al., 2008: 1235, Fig. 5;— Sampaio et al., 2009: 20, Fig. 6;— Pileggi et al., 2013: 116.

Type material. The syntypes are deposited in the Natural History Museum (NHM 7921) in London. Miers (1877) reported the existence of two syntypes collected in Oiapoque, French Guiana. However, only one female was found and analyzed in the mentioned collection (cl 15 mm).

Additional analyzed material. Venezuela, Guarico. USNM 231497, Fundo Masaguaral, coll. Vari et al., 19 January 1983; USNM 228713, Río Orinoco, Isla Tortola, coll. Baskin et al., 19 February 1978.— Brazil, Amazonas. 4 females (cl 5.8–6.8 mm), INPA CR 211, Rio Negro, down rio Daraá, 0°45’S 64°75’W, coll. Goldin, Feb. 1980; USNM 231204, San Jose, Lago Castanho, Janauri, coll. Bayley, 4 December 1978; 4 females (cl 7.5– 8.1 mm), INPA CR 107, Rio Amazonas, Ilha do Careiro, 3°16’S 59°73’’W, coll. Magalhães, 4 November 1981. Pará. 5 males (cl 6.2–6.8 mm), 3 females (cl 5.8–6.9 mm), 2 ovigerous females (cl 8.6–8.7 mm), CCDB 4337, under bridge on the highway, Castanhal, 01°18’6.37’’S 47°59’11.88’’W, coll. Carvalho et al., 14 November 2012; 2 males (cl 4.6–4.75 mm), 1 female (cl 3.49 mm), CCDB 4356, Santa Maria do Pará, 01°22’51.16’’S 47°33’56.42’’W, coll. Carvalho et al., 15 November 2012; 5 females (cl 8.5–9.9 mm), INPA CR 117, Rio Curuá do Sul, near Santarém, 02°26’34’’S 54°42’28’’W, coll. ichthyology team of INPA, 15 November 1977; 1 ovigerous female (cl 11.6 mm), CCDB 4992, Igarapé, Senador José Porfírio 03°05’04,8’’S 51°47’21,1’’W, coll. Robles et al., 2 March 2014. Maranhão. 2 males (cl 7.8 mm), 2 females (cl 7.7–8.7 mm), 2 ovigerous females (cl 7.1 mm), CCDB 1578, Riacho do Brejinho, Caxias, 04° 51’S 43° 21’W, coll. Camara, 13 October 2003. Ceará. 1 female (cl 8.2 mm), CCDB 4569, Açude Bengue, Aiuaba, 6°35’58.2’’S 40°08’30.3’’W, coll. Landim et al., 19 September 2012; 2 females (cl 9.1–10.5 mm), CCDB 4712, Açude Sabiá, Juazeiro do Norte, 7°12’S 39°18’W, coll. Anderson et al., 15 May 2011. Paraíba. 1 female (cl 9.5 mm), CCDB 4568, Rio Piranhas, São Bento, 6°46’80’’S 37°48’77.7’’W, coll. Landim et al., 14 June 2012; 1 male (cl 6.6 mm), 2 females (cl 6.7–9.6 mm), CCDB 1866, Rio Jaguaribe, João Pessoa, 7°05’S 34°51’W, coll. Farias, 21 September 1977. Sergipe. 1 ovigerous female (cl 9.9 mm), CCDB 4567, Rio Itamirim, 11°24’59.5’’S 37°42’19.6’’W, coll. Landim, 26 February 2013. Bahia. 1 male (cl 6.9 mm), CCDB 2625, Ilha de Itaparica, Vera Cruz, 12°54’S 38°40’W, coll. Batista, 15 July 2006; 2 males (cl 6.6–7.9 mm), 2 females (cl 7.7–8.4 mm), 3 ovigerous females (cl 7.7 mm), CCDB 3794, Rio Vermelho, Elísio Medrado, 13°0’0.68’’S 39°30’22.63’’W, coll. Carvalho & Souza-Carvalho, 26 December 2011; 1 female (cl 7.4 mm), CCDB 3796, Mutuípe, 13°13’S 39°30’W, coll. Carvalho & Souza-Carvalho, 25 December 2011; 1 female (cl 8.1 mm), CCDB 2788, Rio de Contas, 13°52’29’’S 40°34’44’’W, coll. Calado, 1 November 2009; 1 female (cl 5 mm), CCDB 1566, Rio Tijuípe, Itacaré, 14°23’55.46’’S 39°02’34.74’’W, coll. Carvalho et al., 11 August 2011; 1 male (cl 6.9 mm), CCDB 1254, Riacho Pancadinha, Uruçuca, 14°27’58.18’’S 39°02’13.34’’W, coll. Carvalho et al., 11 August 2011; 1 female (cl 7.1 mm), CCDB 4355, Riacho Pancadinha, Uruçuca, 14°27.943’S 39°02.207’W, coll. Mantelatto et al., 6 November 2010; 3 males (cl 5.2–7.0 mm), 2 females (cl 6.4–9.2 mm), CCDB 3041, Ilhéus, 15°1.02’S 38°59.93’W, coll. Mantelatto et al., 5 November 2010; 1 female (cl 8.1 mm), CCDB 3087, Rio Jacão, Una 15°17.22’S 39°05.16’W, coll. Mantelatto et al., 5 November 2010; 1 male (cl 5.6 mm), CCDB 1657, Estação Veracel Celulose, Porto Seguro, 16°23’1.97’’S 39°07’34.08’’W, coll. Carvalho & Souza-Carvalho, 15 August 2011; 1 female (cl 6.8 mm), CCDB 4203, stream of Lagoa Grande, Prado, 17°18’13.18’’S 39°13’26.20’’W, coll. Carvalho & Souza-Carvalho, 13 August 2012; 3 males (cl 6.2–6.3 mm), 2 females (cl 5.9–8.0 mm), CCDB 4201, trubutary of the river Jucuruçu, bridge on the highway BA 489, Prado, 17°18’22.42’’S 39°15’17.35’’W, coll. Carvalho & Souza-Carvalho, 13 August 2012. Mato Grosso. 3 males (cl 6.5–7.8 mm), 4 females (cl 7.6–8.1 mm), INPA CR 218, Rio das Pitas, Araputanga, 15°25’44’’S 58°20’39’’W, coll. Py-Daniel et al., 29 September 1984. Minas Gerais. 2 males (cl 6.6–7.4 mm), 3 females (cl 9.4–9.7 mm), CCDB 478, Rio São Francisco, Pirapora, 17°22’5.9’’S 44°56’39.13’’W, coll. Carvalho & Souza-Carvalho, 15 July 2011; 1 female (cl 8.4 mm), CCDB 2952, Pirapitinga, Três Marias, 18°20’S 45°18’W, coll. Jacobucci, 1 November 2009; 2 males (cl 6.6–7.4 mm), 3 females (cl 7.4–8.3 mm), MZUSP 28360, Lagoa Carioca, Marliéria – Dionísio, 19°45’26.3’’S 42°37’6.2’’W, coll. Fragozo- Moura et al., 1 July 2007. Espírito Santo. 3 males (cl 6.3–7.6 mm), 3 females (cl 8.3–8.6 mm), CCDB 2627, Lagoa Grande, Vila Velha, 20°30’S 40°22’W, coll. Mantelatto et al., 3 November 2006; 2 males (cl 5.9–6.5 mm), 2 females (cl 8.2–10.0 mm), 3 ovigerous females (cl 7.6–8.5 mm), CCDB 2628, Córrego Sete, Vila Velha, 20°32’05’’S 40°23'18’’W, coll. Mantelatto et al., 3 November 2006; 1 ovigerous female (cl 8.4 mm), CCDB 2842, Lagoa de Maeaípe, Guarapari, 20°44’20.8’’S 40°32'49.5’’W, coll. Mantelatto et al., 3 November 2006. Rio de Janeiro. 4 males (cl 5.0– 7.5mm), 5 females (cl 6.6–8.8 mm), 1 ovigerous female (cl 9.1 mm), CCDB 4941, Rodovia Italva km 67, Itaperuna, 21°21’39.3’’S 41°42’29.6’’W, coll. Oliveira, 10 October 2013; 1 female (cl 7.0 mm), CCDB 4991, Córrego Caranguejo, Cardoso Moreira, 21°27’43’’S 41°40’54.8’’W, coll. Oliveira, 10 October 2013; 1 female (cl 6.7 mm), CCDB 4650, Pureza, Cambuci, 21°35’14.3’’S 41°50’37.5’’W, coll. Carvalho et al., 24 May 2013. São Paulo. 2 males (cl 4.9–5.1 mm), 2 females (cl 9.1–13.0 mm), 2 ovigerous females (cl 9.6–10.4 mm), CCDB 1562, Rio Grande, Paulo de Faria, 20°01’S 49°24’W, coll. Santos et al., 12 July 2001; 2 males (cl 5.9– 6.5 mm), 3 females (cl 6.8–7.7 mm), CCDB 3520, Clube Náutico de Araraquara, Araraquara, 21°42’17’’S 48°01’33’’W, coll. Peiró, 30 June 2007.

Diagnosis. Rostrum: slender; slightly curved upward; reaches just beyond scaphocerite; reach the end of scaphocerite in fewer cases; one-third distal dorsal rostral margin without teeth; 5–9 dorsal teeth; 1–2 subapical teeth; 1–2 teeth behind orbit; 4–7 ventral teeth. Right and left second pereiopod similar in shape and size; slender; glabrous; carpus bulge at distal end; carpus 1.3 to 2.1 times chela; chela 0.4 to 0.5 the carapace length. Telson: posterior margin ending in a median apex; 2 pairs of plumose setae; 2 pairs of spines; internal pair of posterior spine distinctly surpassing posterior median apex.

Redescription. Rostrum: slender; slightly curved upward; reaches just beyond scaphocerite; reach end of scaphocerite in fewer cases; distal third of the dorsal edge of the rostrum without teeth; 5–9 teeth on the dorsal edge, generally 6 or 7; 1 or 2 subapical teeth on the dorsal edge; 1 or 2 teeth behind the orbit; 4–7 teeth on the ventral edge, generally 6 or 7; rostrum 1.3 to 1.5 times the scaphocerite length (Figure 3 a).

Eyes: well developed; pigmented cornea; eyespot on dorsal side (Figure 3 b).

Antennule: single lower antennular flagellum; upper antennular flagellum divided in two branches, fused in the base to almost 1/3 of the length of the shorter branch. Anterolateral projection of the first antennular segment reaches about 1/3 of the second segment; with rounded margin. Anterolateral spine of the first antennular segment reaches the margin of the anterolateral projection. Projection of the second antennular segment almost reaches the distal margin of the third segment. Stylocerite reaches just before the half of the first antennular segment (Figure 3 c).

Scaphocerite: length about 3.5 times the width; external margin straight or slightly concave (Figure 3 d).

Carapace: smooth; hepatic spine the same size as the antennal spine, placed at an angle behind it; length of the carapace 0.7 to 0.9 times the rostrum (Figure 3 a).

Mouth parts: mandible with 3-segmented palp; setae on all segments; apical setae longer. Molar and incisor process well developed; incisor process with 3 teeth on both mandibles; superior tooth bigger than the other; molar process subdivided in 5 cusps: 2 poorly developed, 2 of median size and 1 well developed (Figure 3 e). Maxillule with bilobated lacinia mobilis; distal lobe with scattered setae; 2 rows of spiniform setae at the apical area; ventral side with few setae; dorsal side of the proximal lobe with many setae, scattered at the base and get more numerous at the apex; upper lacinia curved; internal lacinia curved with a twined spiniform seta (Figures 3 f and 3g). Endopod of the maxilla with two well developed lobes and numerous setae at the apex of both; epipod with a slightly sharp end starting from the fused coxa and basis; operculiform exopod (scaphognathite), well developed, with setae all around the edge (Figure 3 h). First maxilliped with rectangular endopod; convex inner edge; numerous setae at the external edge, invading the dorsal side; laminiform exopod; bilobated epipod, with triangular anterior lobe elongated anteriorly (Figures 3 i and 3j). Second maxilliped operculiform; condyles of the carpus moderately pronounced over the propodus; propodus and dactylus strongly expanded, with numerous setae at the edge directed posteriorly covering the mouth appendices; basis with laminiform exopod, well developed, with setae at the apex; coxa with few setae (Figure 3 k). Third maxilliped pediform and elongated; basis, ischium and merus fused, distally enlarged; laminiform exopod reaches the proximal edge of the carpus; setae at the apex; coxa with lobed epipod; many setae over all segments, mainly the propodus and dactylus (Figure 3 l).

Pereiopods: first pair of pereiopods smooth; distal third of the dactylus reaches the distal margin of the scaphocerite; fingers slightly bigger than the palm, with sharp edges; carpus 1.7 to 3.3 times the length of the chela, 0.9 to 1.6 times the merus; merus almost 2 times the length of the ischium; segments with scattered setae, denser in the ischium and fingers (Figure 4 a). Second pair of pereiopods slender and entirely smooth; most of the chela reaches beyond the scaphocerite; right and left equal in shape and size; ischium slightly shorter than the merus; merus 1.1 to 1.5 times the length of the carpus; carpus slender and smooth with a bulging at the distal end, 1.3 to 2.1 times the length of the chela; length of the chela 5.1 to 6.6 it width; length of the chela 0.4 to 0.5 times the carapace length; cylindrical palm, elongated and slightly flattened laterally; fingers 3/4 of the palm length; cutting edges of both fingers have 1 small tooth at the proximal third; small gap at the proximal third that can bear some indistinct teeth or crenulations (Figure 4 b). Third pair of pereiopods smooth, except for some scattered setae and a row of setae at the posterior margin of the propodus; shorter than scaphocerite; propodus 3.5 times the length of the dactylus; propodus 2 times the length of the carpus; propodus a little smaller than the merus (Figure 4 c). Fourth pair of pereiopods smooth, except for some scattered setae and a row of setae at the posterior margin of the propodus; half of the dactylus reaches beyond the scaphocerite; propodus 4 times the length of the dactylus; propodus 2 times the length of the carpus; propodus is same size as merus (Figure 4 d). Fifth pair of pereiopods smooth, except for some scattered setae and a row of setae at the posterior margin of the propodus; the entire dactylus reaches beyond the scaphocerite; propodus 4 times the length of the dactylus; propodus little more than 1.5 times the length of the carpus; propodus is the same size as the merus (Figure 4 e).

Thoracic sternum: fourth thoracic sternum with median process well developed; forming a triangle; distinct post-coxal edges, posteriorly placed to the median process.

Abdomen: no appendix interna in the first pair of pleopods; endopod reaches half of the exopod in males (Figure 4 f); endopod of females 1/5 to 1/3 the length of the exopod (Figure 4 g). Second pair of pleopods of males bears an appendix masculina (Figure 4 h). Abdominal pleura with setae on the ventral margin (Figure 4 i); pleura of the fifth somite ending in an acute angle; sixth abdominal segment almost 2 times the length of the fifth. Interuropodial sclerite with rounded anal carina, poorly developed.

Telson: almost 1.5 times the length of the sixth abdominal segment; posterior margin ending in a median apex; four dorsal spines, one pair placed at half of the length of the telson and one pair placed more distally; two pairs of posterior spines, the inner ones are slender and strait, distinctly surpass the median apex of posterior margin; internal pair of spine 2.1 to 3.3 longer than median apex of telson; 4 plumose setae between internal spines (Figure 4 j).

Uropods: well-developed stout spine on the lateral end of the diaresis of the uropodal exopod, distinctly longer than the distolateral tooth (Figure 4 k).

Eggs: few and large, major diameter measures 1.9 to 2.3 mm.

Size: analyzed males reached up to 7.8 mm of carapace length; females up to 15 mm. In general females were bigger than males.

Distribution. Trinidad, Suriname, Guyana, Venezuela, Peru, Bolivia, Argentina and Brazil (Amapá, Amazonas, Pará, Maranhão, Ceará, Rio Grande do Norte, Paraíba, Pernambuco, Alagoas, Sergipe, Bahia, Acre, Mato Grosso, Espírito Santo, Rio de Janeiro, Minas Gerais, São Paulo and Paraná) (Pileggi 2009; Boos et al. 2012; Pileggi et al. 2013).

Remarks. The occurrence of M. jelskii in Costa Rica cited by Chace & Hobbs (1969) and Kensley & Walker (1982) is doubtful, uncertain and most probably incorrect. One of us (FLM) has been working on an exhaustive sampling freshwater decapod project in Costa Rica over the last seven years and there is no record there (Wehrtmann & Mantelatto unpublished data). Some disagreements between the morphological information in the literature and the data obtained from this study were observed. To cite some, Holthuis (1952), Collins (2000), García-Dávila & Magalhães (2003), Melo (2003), Pileggi (2009) and Sampaio et al. (2009) reported that the rostrum of M. jelskii distinctly surpasses the scaphocerite, however this proportion was rarely observed in the 122 analyzed individuals, males, females and juveniles of different sizes, including the type material. The rostrum of these specimens is slightly longer than the scaphocerite (i.e. at most one tooth in the ventral edge of the rostrum reaches beyond the scaphocerite) or, in a few cases, is the same size as the scaphocerite. The diagnostic characteristics of M. jelskii can be very similar to those of immature individuals of Macrobrachium amazonicum (García-Dávila & Magalhães 2003; Pileggi 2009) and M. acanthurus. To differentiate them, Holthuis (1952) suggested analyzing the number of teeth of the rostrum, but this character showed to be highly variable and inconclusive. Thus, the ratio of carpus and chela of the second pereiopod is suitable to differentiate M. jelskii and M. acanthurus and this difference was supported by the statistical analysis (p = 4.53·10-10). This ratio is higher in M. jelskii, the carpus of this species is distinctly longer than the chela (between 1.34 and 2.13), while in M. acanthurus the carpus is similar to the chela (ratio of carpus and chela ranges between 0.91 and 1.45). Besides that, the carpus of the M. jelskii is more slender and has an abrupt bulging at the distal extremity than that of M. amazonicum and M. acanthurus. In the last two mentioned species, the proximal part of the carpus is narrow and gradually extends towards the distal part compared to that of M. jelskii. The ratio of the chela of the second pereiopod and the carapace length is also different and statistically supported (p = 5.56·10-8) between M. jelskii (0.38 to 0.54) and M. acanthurus (0.53 to 0.78). Both the rostrum and the telson of M. jelskii and M. acanthurus are alike, but these characteristics are different in M. amazonicum. The rostrum of M. amazonicum is longer than that of M. jelskii, and distinctly surpasses the scaphocerite (two or more teeth on the ventral edge of the rostrum can reach beyond the scaphocerite, although there can be one or no ventral teeth beyond the scaphocerite), it usually has a more evident portion without teeth and is more curved upwards. In adult individuals, the inner posterior spines of the telson usually do not surpass the median apex as those in M. jelskii and M. acanthurus. In smaller individuals of M. amazonicum (carapace length equal or smaller than 5 mm), the inner posterior spines of the telson can exceed the median apex. Differences were found and supported by statistical analysis for the ratio between the internal posterior spine and median apex (p = 3.99·10-9; 2.14 to 3.35 for M. jelskii and 1.16 to 2.11 for M. amazonicum) and the ratio between the internal posterior spine and the carapace length (p = 2.61·10-6; 0.09 to 0.16 for M. jelskii and 0.06 to 0.12 for M. amazonicum —although there is an overlap, the internal posterior spine of M. jelskii tends to be proportionately longer). The mentioned characteristics used to differentiate these three species are summarized in Table 1 and Figure 5. Other morphometric characters, i.e. ratio of the carpus and chela, and the ratio of the carpus and merus of the first pereiopod; the ratio of the merus and carpus, and the ratio of the length and width of the chela of the second pereiopod; the ratio of the carapace length and rostrum; the ratio of the rostrum and the scaphocerite, did not show statistical significant differences and could not be used to differentiate the three species of Macrobrachium.

Other additional reproductive characters that help to differentiate these species are the size and number of eggs. Females of M. jelskii bear larger and fewer eggs (1.9 to 2.3 mm, varies between 10 and 69— Soares 2008; Mossolin et al. 2013) than females of M. amazonicum (0.6 to 0.8 mm, varies between 696 and 2956— Silva et al. 2004; Meireles et al. 2013) and M. acanthurus (0.47 to 0.65 mm, varies between 171 and 7034— Tamburus et al. 2012). These characters are associated with the abbreviated larval development type of M. jelskii (Gamba 1984; Jalihal et al. 1993).