Samadinia Ng & Richer de Forges, 2013

Yan, Bee, Lee, Forges, Bertrand Richer De & Ng, Peter K. L., 2021, The generic affinities of the Indo-West Pacific species assigned to Rochinia A. Milne-Edwards, 1875 (Crustacea: Brachyura: Majoidea: Epialtidae), Raffles Bulletin of Zoology 69, pp. 19-44 : 20-26

Samadinia Ng & Richer de Forges, 2013

( Figs. 1A–E , 2A–D , 3A–D , 4A–M )

Samadinia Ng & Richer de Forges, 2013: 358 .

Type species. Samadinia longispina Ng & Richer de Forges, 2013 , by original designation.

Species composition. The genus as redefined here now contains 26 species ( Table 1).

Comparative material examined. See Appendix 1.

Diagnosis. Carapace pyriform; smooth or covered with either numerous granules or spines ( Fig. 1A–D ). Pseudorostral spines relatively long, slender, diverging at approximately 45° angle or less. Supraorbital eave narrow, preorbital angle acutely triangular; postorbital lobe cup-like, acutely triangular to blunt anterior margin. Carapace with hepatic spine distinct, plate-like or long, sharp; absent to strong lateral branchial spine directed outwards ( Fig. 1A–D ). Antennal flagellum shorter than to longer than pseudorostral spines. Basal antennal article longer than broad, with distinct distolateral angle, outer margin straight to slightly constricted medially. Distal angle of buccal frame blunt, slightly raised. Pterygostomial region with granules or short spines on outer margin ( Fig. 2A–D ). Chelipeds with propodus slightly inflated, carinate margin; carpus with carinate outer margin; merus triangular in cross-section, with carinate margins, with spine or blunt distal angle. Ambulatory legs slender, articles with smooth, rounded margins; merus with blunt distal angle, ventral margin of P2–P5 dactylus typically smooth or with small granules; P2 longest; P5 merus length more than 4 times width ( Fig. 1A–D ). Male thoracic sternum slightly concave anteriorly; sternites 3, 4 transversely narrow, constricted anteriorly, lateral margin relatively straight to constricted medially. Male pleon triangular to trapezoidal, telson triangular to dome-shaped; surface of somites smooth ( Fig. 2A–D ). G1 straight, slender, distal tip sharp or with 2 small distinct projections, slightly constricted on distal third ( Fig. 4A–M ); G2 with distal tip blunt ( Ng & Richer de Forges, 2013: fig. 4D).

Remarks. Samadinia Ng & Richer de Forges, 2013 , was described by Ng & Richer de Forges (2013) for one species, Samadinia longispina Ng & Richer de Forges, 2013 , which differs from other species then referred to Rochinia in having four long spines, poorly defined carapace regions, a granulated carapace, and a transversely narrow male anterior thoracic sternum where sternites 3 and 4 are strongly constricted at the anterior region ( Ng & Richer de Forges, 2013). In their discussion, Ng & Richer de Forges (2013) recognised five groups in Rochinia sensu lato based on the carapace and the male anterior thoracic sternum morphology ( Ng & Richer de Forges, 2013: fig. 5) but refrained from establishing any genera as they noted they had not examined most of the Rochinia species at that time and were unsure about the degree of variation within this taxon.

Since the original description of Samadinia , the authors have examined most of the known species of Rochinia sensu lato, and the above-mentioned characters used to separate them are not all reliable. The carapace armature certainly varies too substantially between species and does not appear to be a useful genus character. Studying the material, it is in fact more parsimonious that we expand the diagnosis of Samadinia to accommodate most of the species now in Rochinia sensu lato. Samadinia is herein redefined to include 25 species that were previously in Rochinia sensu lato ( Table 1).

Of the five groups of “ Rochinia ” recognised by Ng & Richer de Forges (2013), the first included Rochinia gracilipes A. Milne-Edwards, 1875 , and Scyramathia carpenteri (Norman, in Thomson, 1873), species that have distinct, raised carapace regions, with most of the surface smooth but otherwise armed with larges granules or spines, with the male thoracic sternum broad anteriorly and the male pleon acutely triangular to T-shaped (cf. Ng & Richer de Forges, 2013: fig. 5A, B). As discussed earlier, further comparisons by Tavares & Santana (2018) and Lee et al. (2020) have now indicated that the two species belong to separate genera. The second group contained species that have distinct carapace regions, with the rest of the surface smooth but otherwise armed with large rounded granules and low or absent lateral branchial spines, with the broad male thoracic sternum slightly constricted anteriorly, and the male pleon triangular to T-shaped (cf. Ng & Richer de Forges, 2013: fig. 5C). Most of the members of this group were recently referred to a new genus, Crocydocinus , by Lee et al. (2019) (see notes below on Samadinia makassar species-group). The third group contained Rochinia fultoni ( Grant, 1905) as the sole representative, characterised by a relatively elongated carapace, distinct carapace regions with several sharp tubercles, and a narrow male thoracic sternum that is constricted anteriorly and acutely triangular male pleon (cf. Ng & Richer de Forges, 2013: fig. 5F). The male sternum of R. fultoni matches that of Oxypleurodon Miers, 1885 , and although it lacks the typical carapace plate characters, it is here assigned to this genus as it has other associated features (see account of O. fultoni below).

The fourth and fifth groups recognised by Ng & Richer de Forges (2013) are here placed in Samadinia . The fourth group contained species that have distinct carapace regions, with numerous sharp spines on carapace surface, with the male thoracic sternum transversely narrow and constricted anteriorly and the male pleon acutely triangular or T-shaped (typified by R. pulchra ( Miers, 1886)) , while the fifth group has species with distinct carapace regions, a granulated carapace surface, strong lateral branchial spines, and similar male sternal characters as the preceding one (e.g., R. kotakae Takeda, 2001 ). While the carapace morphologies and armature of these two groups appear different, all 18 constituent species share all other diagnostic characters and are here referred to a redefined Samadinia .

In the present paper, two species-groups, with a total of six species, are recognised within Samadinia . There are five species in the S. makassar group, viz., S. daiyuae ( Takeda & Komatsu, 2005) , new combination, S. makassar (Griffin & Tranter, 1986) , new combination, S. moluccensis (Griffin & Tranter, 1986) , new combination, S. suluensis (Griffin & Tranter, 1986) , new combination, and S. tomentosa (Griffin & Tranter, 1986) , new combination. Compared to the other species of Samadinia , these five taxa lack or only have a weak lateral branchial spine, have a prominently rounded posterior lateral carapace margin, with the postorbital lobe flattened laterally, and the preorbital angle is distinct ( Fig. 1B ). These species, however, are rare in collections (Appendix 1), and until more material becomes available, they are provisionally included in Samadinia for now. The other species-group, S. granulosa species-group, includes only S. granulosa ( Ng & Richer de Forges, 2013) , new combination. Ng & Richer de Forges (2013) commented that S. granulosa is morphologically similar to S. longispina in the carapace shape as well as the numerous carapace granules on the surface, but differed in its relatively smaller adult size, with mature females mature at 6.9 mm in carapace width (vs. 9.6 mm carapace width in S. longispina ); the carapace is covered with relatively larger granules ( Fig. 1C ) (vs. carapace with small granules in S. longispina ; Fig. 1A ); the pseudorostral spines are relatively shorter and less diverging ( Fig. 1C ) (vs. longer, more diverging pseudorostral spines in S. longispina ; Fig. 1A ); the male thoracic sternum is proportionately broader anteriorly ( Fig. 2C ) (vs. male thoracic sternum proportionately narrower anteriorly in S. longispina ; Fig. 2A ); and the ambulatory legs are distinctly shorter ( Fig. 1C ) (vs. proportionately longer ambulatory legs in S. longispina ; Fig. 1A ). Until more material or allied species are available, S. granulosa is retained in Samadinia for the time being.

Rochinia debilis Rathbun, 1932 , was described from a single immature female specimen from Joga Shima Light, Japan ( Fig. 1D ). The G1 morphology is figured here for the first time from newly examined males ( Fig. 4J–M ; Appendix 1). Based on the G1 morphology with an angled tip with two small but distinct projections, it is relatively similar to Crocydocinus decipiata ( Williams & Eldredge, 1994) , Tunepugettia sagamiensis and T. corbariae Lee, Richer de Forges & Ng, 2019 . However, as all other carapace and pereiopod characters are closer to Samadinia , this species is here referred to this genus.

Distribution. Across Indo-West Pacific, and East China Sea.

Figures

Fig. 1. Overall dorsal view. A, Samadinia longispinaNg & Richer de Forges, 2013, holotype male (25.3 × 17.9 mm) (MNHN-IU-2011-4190), Polynesia; B, S. suluensis (Griffin & Tranter, 1986) new combination, holotype male (7.8 × 5.0 mm) (RMNH De:103.921), Bougainville Strait; C, S. granulosa (Ng & Richer de Forges, 2013) new combination, holotype female (9.2 × 6.9 mm) (MNHN-IU-2011-2944a), Papua New Guinea; D, S. debilis (Rathbun, 1932) new combination, holotype female (10.8 × 7.0 mm) (USNM49572), Japan; E, S. debilis (Rathbun, 1932) new combination, male (28.9 × 21.0 mm) (SMF 49905), Japan.

Fig.2. Overall ventral view. A, Samadinia longispina Ng & Richer de Forges, 2013, holotype male (25.3 × 17.9 mm) (MNHN-IU-2011-4190), Polynesia; B, S. suluensis (Griffin & Tranter, 1986) new combination, holotype male (7.8 × 5.0 mm) (RMNH De:103.921), Bougainville Strait; C, S. granulosa (Ng & Richer de Forges, 2013) new combination, paratype male (6.5 × 4.6 mm) (MNHN-IU-2011-2944b), Papua New Guinea; D, S. debilis (Rathbun, 1932) new combination, holotype female (10.8 × 7.0 mm) (USNM49572), Japan.

Fig. 3. Lateral view of carapace. A, Samadinia longispina Ng & Richer de Forges, 2013, holotype male (25.3 × 17.9 mm) (MNHN- IU-2011-4190), Polynesia; B, S. suluensis (Griffin & Tranter, 1986) new combination, holotype male (7.8 × 5.0 mm) (RMNH De:103.921), Bougainville Strait; C, S. granulosa (Ng & Richer de Forges, 2013) new combination, holotype female (9.2 × 6.9 mm) (MNHN-IU-2011- 2944a), Papua New Guinea; D, S. debilis (Rathbun, 1932) new combination, holotype female (10.8 × 7.0 mm) (USNM 49572), Japan.

Fig. 4. Left G1. A–C, Samadinia longispina Ng & Richer de Forges, 2013, holotype male (25.3 × 17.9 mm) (MNHN-IU-2011-4190) (after Ng & Richer de Forges, 2007: fig. 4A–D); D–G, S. moluccensis (Griffin & Tranter, 1986) new combination, paratype male (11.5 × 6.9 mm) (RMNH De:103.737), Java Sea; H, I, S. granulosa (Ng & Richer de Forges, 2013) new combination, paratype male (6.5 × 4.6 mm) (MNHN-IU-2011-2944b), Papua New Guinea; J–M, S. debilis (Rathbun, 1932) new combination, male (27.0 × 19.2 mm) (NSMT-Cr 12139), Japan. A, D, H, J, ventral view; B, E, K, ventral view of distal portion; C, G, M, dorsal view of distal portion; F, I, L, dorsal view. Scale bar = 1 mm.