Naxioides elongatus, Arzivian & Alrubaie & Yang & Lin & Zhang & Leong, 2022

Arzivian, Arteen, Alrubaie, Ahmad, Yang, Jessica, Lin, Huiyu, Zhang, Eva & Leong, Rupert, 2022, Crabs (Crustacea, Decapoda) from the Seas of East and Southeast Asia Collected by the RV Hakuhō Maru (KH- 72 - 1 Cruise) 4. South China Sea, Bulletin of the National Museum of Nature and Science. Series A, Zoology 48 (4), pp. 147-191 : 155-159

Naxioides elongatus sp. nov.

( Figs. 4 , 7A–C )

urn:lsid:zoobank.org:act:A7170734-185C-402B-9B18-A2F28FD3DEBF

Material examined. RV Hakuhō Maru KH-72-1 cruise, sta. 50, Ə ( CB 8.8 mm excluding lateral spines, PCL 14.3 mm excluding intestinal spine), holotype, NSMT-Cr 30910; Sta. 54, 1 8 ( CB 12.3 × PCL 16.9 mm excluding intestinal spine), non-type, NSMT-Cr 30911 .

Description of holotype. Carapace ( Fig. 4A, B ) pyriform, surface thickly tomentose; gastric, cardiac, branchial, intestinal regions welldefined, moderately elevated. Gastric region low, with 4 long spines, 10 tubercles; anterior end with 2 acute tubercles just behind base of pseudorostrum; anterior slope medially with slender spine, low, minute spine on both sides; protogastric spines short, directed anterolaterally, followed by 2, longitudinally lined small tubercles; mesogastric spine largest (though broken), erected upright, with 2 transversely lined low acute tubercles. Cardiac region conical, dorsally elongated into long slender spine (though broken), divided on both lateral sides, each with large conical tubercle, lateral surface bearing slender spine. Branchial region not markedly inflated, longitudinally with 2 long, slender mesobranchial spines of similar size, small spine in front of anterior spine, anteromesially with large protuberance bearing small tubercles; lateral subsurface with 3 slender spines of similar size (though second one broken); metabranchial region with small medial spine just anterior to posterolateral carapace margin. Intestinal region elongated posteriorly into large, conical projection (though broken).

Pseudorostrum ( Fig. 4A–D ) distinctly divergent (ca. 30°), straight in lateral view ( Fig. 4C ). Pseudorostral spine slender, dorsal surface weakly ridged toward frontal region, bearing short, subdistal spine dorsomesially (distal part broken). Supraorbital eave ( Fig. 4A–B ) strongly expanded laterally; anterior angle produced into short, blunt preorbital spine erected uprightly; antorbital angle produced into minute conical tooth, directed laterally. Dorsal orbital hiatus rounded ( Fig. 4B ). Postocular cup faintly bilobed ( Fig. 4C ); upper postorbital margin broadly concave (in dorsal view), proximally with distinct rounded intercalated lobe; lateral wall consisting of 2 faint lobes, upper lobe with minute medial tubercle; lower postorbital margin sinuous; small but distinct tubercle right behind ventral orbital hiatus. Pterygostomian region moderately inflated, armed with large conical tubercle directed ventrally ( Fig. 4D ).

Basal antennal article ( Fig. 4D ) narrow, distolateral angle produced anterolaterally into acute tooth, visible in dorsal view; lateral margin generally straight; strong triangular tooth near midlength, directed laterally, as high as distolateral spine. Penultimate antennal articles slender.

Chelipeds slender, tomentose, sparsely covered with long stick-like setae; merus subcylindrical, distally with sharp dorsal spine; carpus globulous; palm slender, generally subcylindrical, slightly compressed distally; fingers almost half of palm in length, occlusal margins finely dentate, contiguous in distal half.

Ambulatory legs with cylindrical articles, surface tomentose, sparsely with long stick-like setae. Merus slender, subcylindrical, distally with sharp dorsal spine.

Thoracic sternites 1–3 unarmed, sternite 4 posteromesially with small spine medially on pleonal cavity, sternites 5–6 with large conical tubercle of similar size, sternite 7 with minute medial spine, sternite 8 unarmed.

Pleon with 6 free somites and telson, each with distinct medial tubercle, lateral part of somites 3–4 roundly elevated.

G1 ( Fig. 7A–C ) shaft stout basally, gently curved laterally, tip sharply pointed, aperture subterminal, without lobular projection.

Etymology. Named for the elongate carapace characteristic for this species.

Remarks. The present new species is close to Naxioides sahulensis from the Sahul Shelf in the previous paper of this series ( Takeda et al., 2022b). However, in the new species, five dorsal spines on the carapace midline are broader than those of N. sahulensis , in which they are immediately narrowed ( Takeda et al., 2022b, fig. 7D; otherwise, the hepatic region bears one minute tubercle and one slender lateral spine in the new species, rather than one small tubercle and two lateral spines in N. sahulensis ( Takeda et al., 2022b, fig. 7); the pterygostomian region is armed with a single large conical spine in the new species, but there are small additional spines on both sides in N. sahulensis ( Takeda et al., 2022b, fig. 7C); the preorbital spine is erect and almost upright in the new species, but only obliquely inclined in N. sahulensis ( Takeda et al., 2022b, fig. 7); the lateral spines on basal antennal article are more anteriorly directed ( Takeda et al., 2022b, fig. 7D) in N. sahulensis than in the new species.

Another close relative, N. tenuirostris ( Haswell, 1880) , shares the upright preorbital angle, but it is much shorter in N. elongatus sp. nov. The antorbital angle in N. elongatus bears a small conical tubercle directed laterally, rather than the more acuminated, posteriorly directed spine in N. tenuirostris as in Griffin (1966, fig. 5). The anterior margin of the lateral orbital wall is bilobed in the new species, but it is entire in N. tenuirostris as seen in Griffin (1966, fig. 8). The cheliped carpus is unarmed in the new species, whereas in N. tenuirostris , it bears two small spines ( Griffin, 1966, fig. 5). In N. tenuirostris , the lateral margins of the male pleon are weakly concave ( Griffin, 1966, fig. 6), but not in the new species.

The male and female specimens of Naxioides elongatus sp. nov. agree in most respects, but the female has a proportionally slightly wider carapace ( Fig. 4A, E ), and the lateral margin of basal antennal article differs slightly from the holotype, with the anteriorly produced distolateral spine (versus anterolaterally) and the slightly anterolaterally directed subproximal marginal spines (versus laterally directed) ( Fig. 4D, H ). Unfortunately, the female is badly damaged, missing the P2 and P5 on both sides, left P4, and pleon, with the damaged and somewhat fragile pseudorostral horns, gastric, cardiac, intestinal, pterygostomian spines and thoracic sternites. Given the poor condition of the female, it is not treated as a paratype.

The carapace of the holotype ( Fig. 4A–C ) is somewhat more elongated than in males either of the two close northern Australian relatives, N. tenuirostris and N. sahulensis from the Torres Strait and the Sahul Shelf, respectively. The young male from the Ogasawara Islands identified as Phalangipus hystrix ( Miers, 1886) by Komatsu (2011) and the record of Naxioides tau- rus ( Pocock, 1890) from the Philippines, 120– 124 m at depth, by Richer de Forger and Ng (2013) may be referable to the present new species.

Griffin and Tranter (1986) largely revised the genus Chlorinoides Haswell, 1880 (type species: Chlorinoides tenuirostris Haswell, 1880 ), and transferred most species of Chlorinoides known at that time to the new genus Thacanophrys . However, Prismatopus Ward, 1933 , has a priority over Thacanophrys as a senior synonym ( Ng et al., 2001; Ng et al., 2008). As regards the systematic position of C. tenuirostris, Griffin and Tranter (1986) mentioned that C. tenuirostris differs significantly from all the other species [of Thacanophrys ] and in respect of the G1, the structure of the orbit and several other features, C. tenuirostris has a much closer relationship to the species of Naxioides than to the species previously grouped with it.

Naxioides elongatus sp. nov., N. sahulensis and N. tenuirostris , might be better assigned to the genus Chlorinoides , as distinct from Naxioides (type species: Naxioides hirtus A. Milne-Edwards, 1865 ). Otherwise, three known species, N. teatui Poupin, 1995 , and N. vaihatu Poupin, 1995 , may belong to the same group with N. elongatus , N. tenuirostris and N. sahulensis .

Distribution. The description of the new species is based on two specimens from the South China Sea; 132–137 and 760–777 m depth. This species probably occurs in the Philippines and off Chichi-jima Island, Ogasawara Islands.

Figures

Fig. 4. A–D: Naxioides elongatus sp. nov., holotype, Ə (NSMT-Cr 30910; CB 8.8mm excluding branchial spines, PCL 14.3mm) from sta. 50. Dorsal (A–B), lateral (C) and ventral (D) views. E–H: Naxioides elonga- tus sp. nov., non-type,8 (NSMT-Cr 30911; CB 12.3×PCL 16.9mm) from sta. 54. Dorsal (E–F), lateral (G) and ventral (H) views.

Fig. 7. A–C: Naxioides elongatus sp. nov., left G1 of holotype, Ə (NSMT-Cr 30910; CB 8.8mm excluding branchial spines, PCL 14.3mm) from sta. 50. Ventral view (A), and distal part of sternal different views (B–C). D–G: Samadinia hakuhoae sp. nov., left G1 (D–F) and G2 (G) of holotype, Ə (NSMT-Cr 30915; CB 10.7mm excluding branchial spines, PCL 16.3mm) from sta. 54. D, in ventral view; E–F, tip enlarged, in ventral and sternal views, respectively; G in sternal view.