Taxonomy of the genus Oriverutus Siddiqi, 1971 (Nematoda: Dorylaimida: Nordiidae)

After introducing its history, the most relevant morphological features of Oriverutus are explained, illustrated (light and scanning electron microscope pictures) and discussed. The taxonomy of the genus is analysed based on the study of all the nominal species, and an emended diagnosis is provided. Its relationships with the closest genera are discussed, and some reflections are made on its phylogeny. Ecanema and Mammillonema are confirmed as junior synonyms of Oriverutus, Inbionema is regarded as its junior synonym also, whereas Paroriverutus is considered to deserve separate generic status. Consequently, several nomenclatorial changes are derived: Paroriverutus ivorensis is retained under Paroriverutus, Drepanodorylaimus macramphidius and Oriverutus longicaudatus are transferred to Paroriverutus, and Inbionema biforme to Oriverutus. An updated list of Oriverutus species is provided as well as a key to the identification of its didelphic species and a compendium of their morphometrics.


Introduction
The genus Oriverutus Siddiqi, 1971 is an interesting dorylaimid taxon for several reasons. With 35 valid species, it is a medium-rich nematode group, although recent contributions (see below) suggest that its diversity is certainly much higher than either known or expected. Its geographical distribution shows a rather special pattern because its representatives mainly inhabit tropical areas of at least three continents (Africa, America and Asia) and two islands or archipelagos (Papua New Guinea and Mauritius), being occasionally found in temperate regions (Korea, Japan, Spain). Morphologically, Oriverutus is a well-characterized genus, distinguishable by a peculiar combination of features: lobe-like lips, odontostyle relatively long and slender with short aperture, pharyngo-intestinal junction often bearing three cardiac cells, and tail conically elongated usually with more or less (but always perceptible) bent dorsad end. Nevertheless, its evolutionary relationships are far from being well elucidated. Originally (Siddiqi 1971) classified under Qudsianematidae Jairajpuri, 1965, it was later (Jairajpuri and Ahmad 1992) accommodated in Nordiidae Jairajpuri and Siddiqi, 1964. After its proposal, several other more or less comparable genera have been described. Leaving aside some morphological variability affecting the lip region, odontostyle and female genital system (mono-opisthodelphic or their identification; besides, this author provided an emended diagnosis of the genus, which was again maintained under Nordiidae, and discussed its affinities with Actinolaimoides Meyl, 1957 andMalekus Thorne, 1974. Ahmad and his collaborators Ahmad and Araki 2002;Ahmad and Shaheen 2003;Baniyamuddin and Ahmad 2007) described several new species. Andrássy (2009) mentioned that Oriverutus included 27 species (although their list was not provided by the author), classified it under the new subfamily Oriverutinae, regarded Ecanema Ahmad and Shaheen, 2005 as its junior synonym, and mentioned that Inbionema Loof and Zullini, 2000 might be identical to it.  and  studied six (three new and three known) species from Costa Rica. And, very recently, Peña-Santiago et al. (2013) provided a revision of the 13 opisthodelphic Oriverutus species, three of them being new.

Main morphological features and their taxonomical interest Lip region and amphids
As observed using light microscopy ( Figure 1), it appears offset from adjacent body by a more or less marked depression, occasionally a constriction ( Figure 1D). It is  Ahmad and Jairajpuri, 1987; (C) Oriverutus belloi (D) Oriverutus costaricensis ; (E) Oriverutus hemihystera ; (F) Oriverutus kalikus Gambhir et al., 2008; Oriverutus sundarus (Williams 1964) Siddiqi, 1971; (H) Oriverutus tropicus Ahmad and Shaheen, 2003. Scale bars: A-F, H = 10 µm; G = 5 µm. very often visibly but moderately expanded, i.e. slightly wider than the adjacent body region. Its general profile is comparatively high since the lip region is only about 2.5 times as wide as high, and very angular. The lips are conspicuously separated, with distinctly protruding labial and cephalic papillae. And the perioral area is also characteristically elevated and projecting, nearly reaching the level of lip tips. The amphid aperture is large, occupying about three-quarters of the lip region diameter. This pattern is typical of the genus, present in most of its representatives. Nevertheless, some species show some variations especially regarding the height and separation of lips and/or the protrusion of their papillae.
Observations by SEM (Figures 2 and 3) confirm those obtained with light microscopy and allow a better explanation and understanding of the nature of the lip region. Lips are high, lobe-like, and totally separated by the existence of deep radial incisures. Lateral lips are appreciably larger than the subdorsal and the subventral ones, especially at their base. Both subdorsal lips and both subventral lips are visibly separated between them and closer to their respective lateral lip, so it is possible to divide the lip region into two sides (left and right; easily perceptible in Figure 2E). Labial and cephalic papillae are button-like, always protruding on the surface of lips. Perioral area is also high, lobe-like and projecting, reaching the level of lip tips, and, as seen in frontal view, it seems a central, oval, dorsoventral, ring-like structure, separated from the lips by a well-marked circular incisure. The oral aperture is a short dorsoventral slit surrounded by the central lobe. Hence, the lip region shows a discernible bi-radial symmetry. Amphid aperture is a large transverse slit, nearly running the lip region width.
When proposing Oriverutus as new genus, Siddiqi (1971; see also Jairajpuri and Ahmad 1992) did not emphasize the morphology of the lip region to characterize this taxon, but Andrássy (2002Andrássy ( , 2009 did. Despite SEM pictures only being available for a few species, the observed lip region pattern is probably common within the genus, but further species should be studied with SEM to elucidate the variability affecting this character. Especially remarkable for this pattern are the bi-radial symmetry and the shape adopted by the perioral area: a protruded, lobe-like structure, distinctly delimited or separated from the lips. This pattern certainly supposes an apomorphic condition and the most characteristic diagnostic feature of the genus.

Odontostyle
It is attenuate, i.e. relatively long, slender and with small aperture (Figure 1). Always exceeding the lip region diameter, the odontostyle length usually varies from 10 to 25 µm or 1.2 to 2.5 times the lip region width. It is often at least 10 times as long as wide and its aperture, not always well visible, very frequently occupies less than onefifth of total length, but occasionally may be larger ( Figure 1H).
Odontostyle morphology is used as a relevant diagnostic feature of the genus, especially to establish its evolutionary relationships (see below).

Pharynx
It is typical dorylaimoid, consisting of a slender but muscular anterior section that enlarges gradually, and a moderately developed basal expansion that very often occupies two-fifths to one-half of total neck length, seldom exceeding this range. Pharyngeal gland nuclei are often small and not too much conspicuous: DN is located at an appreciable distance from DO; S 1 N are especially small and difficult to observe, but they are well apart and located at the anterior half of the basal expansion; and S 2 N are found far from the pharyngeal base at about 85-90% of total neck length.  Ahmad and Jairajpuri, 1987;(B, E) Oriverutus sundarus (Williams, 1964) Siddiqi, 1971; (C, F) Oriverutus tropicus Ahmad and Shaheen, 2003; (G-I) Oriverutus occidentalis Peña-Santiago and Peralta, 1991. A-C: Sublateral or ventral view; D-E: frontal view. Scale bars 5 µm.

Pharyngo-intestinal junction
It displays relevant and interesting diversity ( Figure 4). A more or less developed (often small) valve-like structure (the cardia) is always present. In a few species (for example, O. belloi, O. papillatus and O. tropicus) the cardia is asymmetricalits dorsal side bulges in a perceptible lobe ( Figure 4A, B). Most species bear three cardiac cells ( Figure 4C-E). And several forms have a dorsal cell mass just behind the cardia level and/or at the anterior end of intestine ( Figure 4F). These variations (asymmetry, cardiac cells and dorsal cell mass) should be regarded as apomorphic conditions of their respective characters, but, not being present in all the species, their value as diagnostic features to define and to distinguish the genus is questionable. The absence of cardiac cells might be interpreted as a secondary loss.

Female genital system
Thirteen species are mono-opisthodelphic whereas the remaining are didelphicamphidelphic. Among amphidelphic species, O. hemihystera has the anterior genital branch less developed (but apparently functional) than the posterior one. Most opisthodelphic species totally lack a pre-vulval uterine sac ( Figure 5A), which occasionally becomes very short (e.g. in O. tropicus; Figure 5D); exceptionally, only O. vanisti displays a large sac with vestigial oviduct and ovary. The uterus is the most variable structure in the genus, often being simple ( Figure 5A), but bipartite ( Figure  5B) or tripartite ( Figure 5C) in some species; its distal portion, close to the sphincter, occasionally bears special differentiation such us the presence of refractive elements ( Figure 5B). The vagina usually consists of pars refringens, but this is lacking in a few species ( Figure 5E). The vulva is a transverse slit, but pore-like in O. lobatus.
Variation observed in the morphology of the female genital system is very useful to characterize and separate Oriverutus species, but it does not show any regular pattern.

Male genital system and accessory elements
Males are known only in two of the 13 opisthodelphic species: O. vanisti has males as frequent as females, and a unique male specimen has been reported for O. sundarus. In contrast, didelphic species often have both females and males equally frequent. As usual, no relevant intrageneric variation is observed in the morphology of the male genital system, but secondary sexual structures show some interesting differences. In addition to the ad-cloacal pair, there is a series of one to eleven, more or less regularly spaced, ventromedian supplements, which are often located outside the range of spicules (i.e. hiatus is present), but that in two cases, namely O. anisi and O. arcuatus, the posteriormost are situated at the level of the anterior end of spicules or slightly within their range, and in three species (O. ecae, O. masculus and O. maturitatis) lack hiatus and have one to three ventromedian supplements within the range of spicules. Spicules are relatively small, ranging from 22 to 40 µm long, and weakly sclerotized.
The number and arrangement of ventromedian supplements are also useful to characterize and separate species, but do not follow a definite pattern. Spicules do not provide much interesting information for taxonomic purposes.

Caudal region
It is always conical with more or less rounded terminus, basically similar in both sexes ( Figure 6). Its most significant variation affects its curvature and its size (length). In many species the ventral side of tail is nearly straight ( Figure 6B, C, H) or slightly curved ventrad ( Figure 6A, E), whereas the dorsal side appears regularly convex ( Figure 6E) but very often with a more or less developed (almost always easily perceptible) terminal concavity ( Figure 6A-C, G). Several species, however, show regularly and visibly curved ventrad caudal region ( Figure 6D, F). The inner core of tail may reach the tail tip ( Figure  6A, G), but, more often, it does not reach the tip and a more or less developed hyaline, terminal portion is easily perceptible ( Figure 6B, D, E, H). Tail shape and size show relevant intrageneric, but also some intraspecific, variation, and should be taken with caution to characterize the genus and to separate its species.

Emended diagnosis
Small-to medium-sized nematodes, 0.56-2.21 mm long. Cuticle with two, occasionally three, layers. Lip region high, with bilateral symmetry: lips distinctly separate, lobe-like, the lateral ones larger than the subdorsal and subventral; papillae visibly protruding on the surface of lips; perioral area an elevated (also lobe-like) structure, well demarcated from the adjacent lips and surrounding the oral aperture, which is a dorsoventral slit. Amphid aperture occupying most of lip region diameter. Odontostyle attenuate, 10-26 (39-66 in E. biformis) µm long and longer (up to three times) than lip region diameter; aperture small, usually up to one-fifth its length, exceptionally larger. Guiding ring simple. Odontophore rod-like. Pharyngeal expansion occupying up to one-half of total neck length. Cardia symmetrical or asymmetrical, bearing or not three cardiac cells. Female genital system didelphicamphidelphic or monodelphic-opisthodelphic. Pars refringens vaginae usually present, seldom absent. Uterus often simple and short, occasionally bi-or tri-partite. Vulva transverse (pore-like in O. lobatus), often pre-equatorial. Male with one to twelve spaced ventromedian supplements, with or without hiatus. Tail similar in both sexes, conical, more or less curved ventrad, often slightly bent dorsad at the end.

Ecanema
When originally proposed, this genus had E. ecae as its type and only species, Ahmad and Shaheen (2005) distinguished it from Oriverutus on the basis of three main differences: the tripartite (versus bipartite) nature of pharynx, S 1 N 1 of similar (versus dissimilar) size as DN, and absence (versus presence) of hiatus. Andrássy (2009) regarded Ecanema as a junior synonym of Oriverutus, stating that (p. 375) "neither the oesophageal structures nor the position of the supplements show any differences between these genera".  studied in detail one female of E. ecae (reported as Oriverutus ecae) from Costa Rica and found that it fits the Oriverutus pattern very well, especially regarding the most characteristic feature of this genus, the lip region morphology ( Figures 1F and 7A), hence accepting Andrássy's (2009) criterion. Nevertheless, O. ecae is a peculiar member of Oriverutus by having especially slender (but not non-muscular, as originally described) anterior portion of pharynx, a comparatively long pharyngeal enlargement with a characteristic narrowing ( Figure 7E), and refractive elements at the distal portion of uterus, close to the sphincter ( Figure 5B), but these characters should be interpreted as intrageneric rather than intergeneric variations. Regarding the size of S 1 N 1 compared with DN, a re-examination of the female of O. ecae studied by  confirmed that S 1 N are larger than S 2 N and that S 1 N are more or less similar in size to DN ( Figure 7B-D); nevertheless, an identical scheme occurs in other Oriverutus species, for instance in O. tropicus, as revealed by the re-examination of well-preserved specimens of this species. Obviously, the absence of hiatus in O. ecae is not a relevant difference because at least two other Oriverutus species bear ventromedian supplements within the range of spicules (see above). Hence, Andrassy's action, synonymysing Ecanema with Oriverutus, is solidly founded and well justified. Darekar and Khan (1982) described the new genus Mammillonema, with M. mammillatus as its type and unique species, and compared it to Oriverutus, from which it was separated by a series of seriously questionable differences: mammillate papillae, nature of odontophore ("spear extension asymmetrical, zig-zag anteriorly"), both pharyngeal regions nearly equal in length, female genital system didelphic, and mammillate ventromedian supplements. Only the differences observed in odontophore nature might be of some taxonomical relevance, but such a "zig-zag" design has not been described in dorylaims, and is often the result of inadequate killing and fixation processes. Jairajpuri and Ahmad (1992) regarded Mammillonema as identical to Oriverutus and transferred its only and type species to the latter, an action that seems to be well justified and herein accepted.

Paroriverutus
This genus was described by Carbonell and Coomans (1982), with P. ivorensis from the Ivory Coast as its type and only species. The new taxon, morphologically close to Oriverutus, was separated from this (p. 899) "in having a longer odontostyle, more posterior position of guiding ring, more posterior position of S 1 N 1 and S 1 O 2 , less developed glandular tissue at the pharyngo-intestinal junction and much longer tail". After describing three new Oriverutus species with comparatively long odontostyle, weakly developed glandular tissue near the cardia and/or conical elongate caudal region, Ahmad and Siddiqi (1997) considered that differences between both genera were not enough to maintain separate generic status, synonymised Paroriverutus with Oriverutus, and transferred P. ivorensis to Oriverutus. This action was accepted by Andrássy (2002Andrássy ( , 2009. The excellent original description of Paroriverutus allows re-evaluating and updating its comparison with Oriverutus. Three relevant features of this genus, namely lip region hemispherical with completely fused lips, guiding ring double and tail long in both sexes (196-232 µm, c = 6.2-6.9, c' = 8.4-9.0 in females), conform to a morphological pattern that significantly differs from that observed in Oriverutus and support the separation of both taxa. Consequently, Paroriverutus is considered to be a valid taxon, distinguishable from Oriverutus by its lip region hemispherical with amalgamated (versus distinctly separated, lobe-like) lips, double (versus simple) guiding ring, and longer caudal region (> 190 versus < 160 µm). Andrássy (1971) described the new species Drepanodorylaimus macramphidius from Angola, which, three decades later (2002), was transferred to Oriverutus by the same author. This species is characterized by, among other features, its lip region with amalgamated lips, double guiding ring and long female tail (152 µm, c = 8.3, c' = 9.5), which is very similar to those found in Paroriverutus pattern.
Oriverutus macramphidius and O. longicaudatus are very close to Paroriverutus ivorensis, having in common the double guiding ring (a relevant feature in dorylaims) and the long tail. Besides, it is also remarkable that these three species are only known to occur in western Africa and might share a recent common ancestor. For these reasons, the former taxa are transferred to Paroriverutus as P. macramphidius (Andrássy 1971) comb. nov. and P. longicaudatus (Ahmad and Jairajpuri, 1997) comb. nov., respectively. Doing so, Oriverutus and Paroriverutus become more homogeneous taxa, easily distinguishable on the basis of the guiding ring (simple versus double, respectively) and length of tail (< 100 µm, c < 10, c' > 5 versus > 100 µm, c <10, c' > 6). Another tentative difference between the genera could be the morphology of lip region, but further studies are needed to clarify this matter.

Inbionema
Loof and Zullini (2000) described the new genus Inbionema from Costa Rica, with I. biforme as its type and only species. It was distinguished from Oriverutus in body size (more than 1.5 versus under 1.3 mm in Oriverutus), the morphology of lip region (lips deeply separate versus partly separate; two circles versus one circle of papillae in lateral view), odontostyle length (> 38 versus up to 18 µm), arrangement of S 1 N (close together versus far apart), cardiac cells (absent versus present), tail length (c' = 1.1-1.6 versus 1.9-5.6), and shape of spicules (very thick versus normal). One female and one male paratype, deposited in the nematode collection of the University of Jaén (Spain), were available to study (Figure 8). Light microscope and SEM pictures (see Figure 8A, D and Loof and Zullini's Fig. 6, respectively) show that the lip region of Inbionema is totally comparable with that found in Oriverutus species (Figure 2 in this contribution), with no significant difference. Regarding the location of pharyngeal gland nuclei, it displays a pattern ( Figure 8B) similar to that observed in some Oriverutus species, for instance O. ecae and O. tropicus (see above). It is now known (see above) that cardiac cells may be either present or absent in Oriverutus species. Hence, the main differences between these genera are reduced to morphometrics, since I. biforme is significantly larger than Oriverutus species, although, taking into consideration the current described diversity for the former genus, such differences are now smaller: body length (1.5-2.2 versus up to 1.26 mm in O. occidentalis), odontostyle length (39-66 versus up to 26 µm in O. longistylus) -it is remarkable that Loof and Zullini emphasized that within the same population they found two groups of specimens significantly differing in odontostyle length, 39-43 and 59-66 µm, without intermediate values-, tail length (c' = 1.1-1.6 versus c'= 0.8-1.8 in O. ecae), and spicule length (69-85 versus up to 40 µm in O. pagarus). Andrássy (2009) stated (p. 373) that "Inbionema strongly resembles Oriverutus …, these genera may be identical". Taking into account that Oriverutus seems to be a highly diverse taxon in Costa Rica, the species described as I. biforme might represent one of its evolutionary lines in which the general size suffered an important increase. Then, Inbionema is herein considered to be identical to Oriverutus, and its only species transferred to the former genus as Oriverutus biformis (Loof and Zullini 2000) comb. nov.

Oriverutoides
The only and type species of this genus, Oriverutoides attenuatus from New Zealand, resembles some representatives of Oriverutus in the morphology of lip region with protruding papillae, attenuate odontostyle, opisthodelphic female genital system and tail shape. Ahmad and Sturhan (2002) originally distinguished it from Oriverutus in the more posterior location of DO, DN and amphid aperture (versus more posterior than usual), sclerotized cheilostom and the absence of cardiac cells. Re-examination of type material (three female paratypes) of Oriverutoides attenuatus (Figure 9) confirms the resemblance between this species and some representatives of Oriverutus. Unfortunately, the differences between them cannot be totally confirmed herein. On one hand, the position of the amphid aperture is quite posterior ( Figure  9E, F), more than usually observed in Oriverutus, as mentioned by Ahmad and Sturhan (2002); besides, the aperture is a comparatively large oval, not a transverse slit as often occurs in Oriverutus species (Figure 2). On the other hand, the location of pharyngeal gland nuclei and their outlets is obscure in the three available specimens; and the existence of sclerotization in the cheilostomatal walls seems questionable since the best preserved female does not show any distinct differentiation in cheilostom ( Figure 9A) whereas in another female, in a worse state of preservation, it is possible to distinguish two small granular bodies ( Figure 9B) at both sides of the cheilostom, which might represent the inner core of the respective lips. Of course, the absence of cardiac glands is not a difference between Oriverutoides and Oriverutus (see above). Consequently, and taking also into consideration the geographical distribution of Oriverutoides, which is far from the current known range of Oriverutus, both genera are provisionally considered as valid and separate taxa.

Parapalus
When proposing this genus, with Parapalus arboricola from Costa Rica as its only and type species, Loof and Zullini (2000) classified it under Qudsianematidae, Paraxonchiinae due to its neck strongly tapering forwards, the lip region becoming (p. 609) "less than 25% of body diam. at base of pharynx". Parapalus was not compared with Oriverutus and its closest genera. The taxonomy of paraxonchiid taxa suffered some changes during the next decade (cf. Baniyamuddin et al. 2010), but the concept and status of Parapalus remained invariable. The re-examination of type material of Parapalus arboricola has revealed ( Figure 10) that the general morphology of this taxon resembles in many aspects to that of Oriverutus (lip region visible expanded, odontostyle longer than lip region, conical tail with a weak dorsal concavity), but also confirmed that the neck region strongly tapers towards the anterior end, with very narrow lip region ( Figure  10A-C), a remarkable feature indeed. Besides, lips are separated but probably not lobelike ( Figure 10D-F), odontostyle is relatively robust, and the pharyngo-intestinal junction lacks gland cells but the cardia is distinctly asymmetrical (Figure 10G), all these features being unusual but not unknown in Oriverutus species. Parapalus arboricola might represent an extreme case within the potential variability of the genus Oriverutus, but, taking into account that the strong tapering of the neck region is a relevant qualitative apomorphic state, not described in Oriverutus, Parapalus is accepted as a valid genus, provisionally distinguishable from Oriverutus.

Dorydorella
Originally created (Andrássy 1987) to accommodate three Eudorylaimus species with comparatively long odontostyle (1.3-2.0 times the lip region diameter), Dorydorella is a poorly characterized genus. It resembles Oriverutus in its general appearance and odontostyle length, but both genera are provisionally distinguishable by the morphology of lip region (lips not lobe-like and perioral area barely differentiated in Dorydorella) and of female tail (always straight ventrally and up to twice the anal body diameter in Dorydorella). Nevertheless, further studies should be undertaken to elucidate the relationships between these two genera.

Kochinema
It can be separated from Oriverutus in a peculiar combination of characters: lip region distinctly expanded, much wider than adjacent body, amphid aperture in anterior (labial) position and double guiding ring.

Longidorella
Also bearing a long odontostyle, this genus differs from Oriverutus in the morphology of lip region (versus lips not lobe-like and perioral area scarcely differentiated), and larger (versus usually three times the lip region width long or more, but occasionally shorter) and more slender (flexible) odontostyle. Besides, Longidorella species are, in general, smaller and stouter; and their tail is conical and regularly curved ventrad, more rarely straight ventrally or conoid to rounded.

Malekus
This taxon and Oriverutus have in common the distinctly protruding papillae in lip region and the comparatively long odontostyle. Nevertheless, they differ in the morphology of lips (versus amalgamated in Malekus), odontostyle (versus much slender, needle-like), and guiding ring (versus apparently double).

Phylogeny
As they can be derived from available data, and in agreement with the new concept herein proposed, evolutionary relationships of Oriverutus become intricate. Originally classified under Qudsianematidae on the basis of its general morphology (Siddiqi 1971), it was later included in Nordiidae because of its relatively long and slender odontostyle (Jairajpuri and Ahmad 1992). However, both families are certainly artificial (polyphyletic) taxa, which lack a convincing morphological characterization and do not find molecular support (Holterman et al. 2008;Pedram et al. 2011), a proof that odontostyle morphology has probably been overestimated in the taxonomy of dorylaims (Dorylaimina) and that brings the question to the general problem of Dorylaimoidea phylogeny.
From the morphological perspective, Oriverutus pattern (lips lobe-like, long odontostyle, cardiac cells usually present, mono-opisthodelphy in many species, female tail often conical elongate and bent dorsad at the end, etc.) is easily recognizable and does not compare to others. Oriverutoides is very close to Oriverutus, but it shows some relevant evolutionary novelties (sclerotized cheilostom, backwards migration of amphid aperture and DN; see above) that make it difficult to assess if either both taxa share a recent common ancestor or the former derives from any evolutionary line within the latter. Biogeographical evidence seems to support the second hypothesis because no Oriverutus species has been reported from New Zealand, a country whose nematode fauna is acceptably known. Relationships among Oriverutus and Paroriverutus (guiding ring double, long tail; see above) might not be as close as assumed, the latter provisionally being a taxon only distributed in western Africa. Also, Malekus displays significant differences when compared with Oriverutus. Andrassy's action (2009), proposing the new subfamily Oriveturinae to group Oriverutus and their relatives (Inbionema, Malekus and Oriverutoides; Paroriverutus regarded as identical to Oriverutus, see above), is hence not totally justified; it should be taken with caution and be the matter of further analysis. Additional studies are also needed to clarify the relationships of Oriverutus with Longidorella and, very especially, with Dorydorella.
Unfortunately, no molecular data of Oriverutus and its closest relatives are available. This poses a major limitation to elucidate their systematics.

Not included in the key
Oriverutus masculus: known only on the base of male specimens. Additional information on Oriverutus didelphic species is provided in Table 1, where a compendium of their main measurements and ratios is presented together with their geographical distribution and the corresponding references. For a key and a compendium of opisthodelphic species, see the recent contribution by Peña-Santiago et al. (2013).    of technical staff and the equipment of the Servicios Técnicos de Investigación, University of Jaén.