Ovatis Ng & Chen 2004, new genus
Creators: name: Ng, Peter K. L.
name: Chen, H. - l.
Publisher: name: Zenodo
Year: 2004
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Xanthidae
Ovatis

description: Ovatis, new genus
Type species. Ovatis simplex, new species, by present designation.
Diagnosis. Carapace ovate, broader than long; regions glabrous, poorly defined; anterolateral margin entire, convex, not cristate, junction of antero- and posterolateral margins clearly demarcated by angle; ocular peduncle unarmed. Posterior margin of epistome with lateral lobes triangular, projecting into buccal cavity. Cheliped segments without ridges or crests. Ambulatory legs relatively slender, merus with low dorsal crest. Anterior thoracic sternites 2 and 3 separated by distinct suture between sternites 3 and 4, medially incomplete. Male abdomen occupying entire space between coxae of fourth ambulatory legs, a small part of thoracic sternite 8 visible when abdomen closed; segments 3–5 fused, without trace of sutures. G1 relatively stout, distal part dilated, with numerous long plumose setae.
Etymology. The genus name is derived from the Latin ‘ ova ’ for egg, in arbitrary combination with ‘- gatis ’, a common suffix for crabs in this family. It alludes to the shape of the carapace of the type species. The gender is masculine.
Remarks. With regards to the ovate carapace with its entire and rounded anterolateral margins, Ovatis, new genus, most closely resembles Liagore De Haan, 1833, but can be separated by its relatively broader carapace (figure 1a versus figure 4a), with the antero- and posterolateral margins separated by a relatively sharp angle (figure 1a, b) (versus gently rounded, figure 4a, b), the carapace regions just discernible (figure 1a, b) (versus not visible, figure 4a, b), the median part of the posterior epistomal margin low and the lateral parts prominently expanded (figures 2a, 3c) (versus median part triangular with the lateral parts low), the anterior thoracic sternum proportionately broader (figures 2c, 3f versus figure 4c), and the G1 stout, short with the distal part dilated (figure 3g, h) (versus elongate, slender, with tapering tip; figure 5a, b, d–f). These characters are independent of size. In addition, the outer distal angle of the carpus of the cheliped of adult Liagore has a distinct tooth projecting outwards (absent in Ovatis, figures 1a, b, 2b). This tooth is low and less obviously developed (figure 4a, b) but still discernible in smaller specimens of Liagore comparable in size to the type specimens of Ovatis. Ovatis simplex is a small-sized species, with both type males examined here already mature. Small specimens of L. rubromaculata (De Haan, 1835) examined that are comparable in size to the types of O. simplex are still immature, with the G1 poorly developed (e.g. male, 10.4 x 7.8 mm, IOCAS K15513 -39, figure 5d). Female specimens of L. rubromaculata comparable in size to the types of O. simplex are still immature, with the abdomen triangular and the pleopods barely developed (e.g. female 24.9 x 17.5 mm, IOCAS, station 6105).
The carapace shape of Ovatis also allies it with the monotypic xanthid genera Paratergatis Sakai, 1965 (type species Paratergatis longimanus Sakai, 1965) and Pulcratis Ng and Huang, 1997 (type species Pulcratis reticulatus Ng and Huang, 1997). Paratergatis longimanus has been reported from Japan to Taiwan and South Africa (Sakai 1965a, 1965b, 1976; Kensley, 1969; Serène, 1984; Jeng and Ng, 1998) and is now recorded from the northern part of the South China Sea (present study). Pulcratis reticulatus was originally described from southern Taiwan (Ng and Huang, 1997) and is now known from further south in the South China Sea (present study). Ovatis can, however, be immediately distinguished from both these genera by its rounded anterolateral margin (versus distinctly cristate), the prominently expanded lateral parts of the posterior epistomal margin (figures 2a, b, 3c) (versus low; figure 6c), and G1 proportionately shorter and more sinuous (figure 3g, h) (versus proportionately longer, almost straight). Ovatis can also be distinguished from Paratergatis by its proportionately narrower carapace (figures 1a, b versus 6a, b, 7c), the entire anterolateral margin (figure 1a, b) (versus with low lobes; figures 6a, b, 7c), the smooth palm of the chela (figure 1) (versus with low dorsal crest; figures 6a, 7a), the completed fused male abdominal segments 3–5 without any trace of sutures (figure 3d) (versus with lateral parts of sutures still discernible; figure 7b), and the male abdominal segment 2 longitudinally broader (figure 3d) (versus relatively narrower). Ovatis can also be separated from Pulcratis by its unarmed eyestalk (figure 3b) (versus with sharp granules), proportionately longer legs without distinct dorsal and ventral crests (figure 1a) (versus shorter with strong crests), the smooth palm of the chela (figures 1, 2b) (versus with prominent dorsal crest; figures 8a, b, 9a, b), the simple tooth on the inner angle of the carpus of the cheliped (figures 1a, b, 2b) (versus with prominent lamellar tooth), and the relatively stouter and shorter G1 without any lateral projection (figure 3g –j) (versus relatively longer and more slender with inner subdistal projection).
The subfamilial placement of Ovatis is somewhat difficult, akin to the problems facing the taxonomic position of Liagore De Haan, 1833 (type species Cancer (Liagore) rubromaculata De Haan, 1835). While Liagore is typically xanthoid, its familial position has been uncertain and it has been unplaced in modern classifications (e.g. Guinot, 1971; Serène, 1984). The carapace features of Liagore are superficially similar to those of Carpilius Desmarest, 1823, in the Carpiliidae Ortmann, 1893. However, in members of the Carpiliidae, the G1 is stout and the G2 very long. The G1 and G2 of Liagore, however, are typically xanthid s. str., with the G1 slender and the G2 very short (figure 5). Liagore currently contains just two species, L. rubromaculata (De Haan, 1835) from the western Pacific and L. erythematica Guinot, 1971, from the Indian Ocean. A recent study also does not support any close relationship between Carpilius and Liagore (Wetzer et al., 2003). Within the Xanthidae MacLeay, 1838, Liagore is perhaps best placed in the Xanthinae (sensu Serène, 1984). The smooth and rounded carapace of Liagore, without discernible regions, however, is rather atypical for xanthines. Ovatis bridges the gap. Its carapace is smooth, but the surfaces are punctate, and the regions are just visible. In Liagore, the antero- and posterolateral margins are not well demarcated, gently merging, giving the carapace a more rounded appearance. In Ovatis, the antero- and posterolateral margins are also more clearly separated. Both genera are here referred to the Xanthinae MacLeay, 1838.
The close affinities of Ovatis with Paratergatis and Pulcratis also cast doubt on the validity of the Xanthinae and Zosiminae Alcock, 1898 (see also Clark et al., in press). Paratergatis and Pulcratis are currently placed in the Zosiminae. The only character that effectively distinguishes the Xanthinae and Zosiminae at present is whether the ambulatory segments are cristate but this is unlikely to have significant phylogenetic significance. In Ovatis, while none of the segments of the ambulatory legs are distinctly cristate, it can be described as weakly so; and those of Paratergatis are only weakly cristate. With regards to their general features, Paratergatis, Pulcratis, Ovatis and Liagore all appear to be related and as such, their present allocation into two separate subfamilies seems difficult to justify. Guinot (1971: 1096, figure 5) noted that in Liagore, a part of thoracic sternite 8 was visible even when the male abdomen was completely closed. This exposed part articulates with the anterolateral corner of the fourth ambulatory coxa. In Ovatis, the exposed part of sternite 8 is relatively much smaller than that of Liagore (ca only one-fifth the size), being barely discernible, which is also the case for Pulcratis and Paratergatis. In some other xanthines (e.g. Leptodius and Xantho) we have examined, no part of thoracic sternite 8 is visible when the male abdomen is closed. However, the value of this character in defining the subfamilies in question can only be ascertained when the various genera involved are revised.
Some taxonomic remarks on Liagore rubromaculata and L. erythematica are pertinent in view of the good series of specimens available for this study (see Comparative material). Guinot (1971) established L. erythematica on the basis of only one dried specimen from the Indian Ocean, noting that it differed from L. rubromaculata mainly in the anterolateral margin having lobes (versus completely smooth and unarmed). The present series of specimens of both species of Liagore demonstrate that this is a useful character, although only large specimens have the anterolateral lobes prominently developed, smaller ones have them relatively lower. In L. rubromaculata, however, there is never any trace of lobes, regardless of the size of the specimens. In addition, their G1 structures are different, with that of L. rubromaculata being relatively more curved (especially along the distal half) (figure 5a, b versus figure 5e, f).
description: Published as part of Ng, Peter K. L. & Chen, H. - l., 2004, On a new genus and new species of xanthid crab (Crustacea, Decapoda, Brachyura, Xanthinae) from the South China Sea, with notes on the genus Liagore De Haan, 1833, pp. 2345-2360 in Journal of Natural History 38 (18) on pages 2346-2356, DOI: 10.1080/00222930310001647352, http://zenodo.org/record/5250420