Choniognathus spinosus, Forges & Lee & Ng, 2021

Forges, Bertrand Richer De, Lee, Bee Yan & Ng, Peter K. L., 2021, The taxonomy of spider crabs of the genera Eurynome, Choniognathus, Seiitaiodes and Kasagia (Crustacea: Brachyura: Majidae) from southwest Indian Ocean, Zootaxa 5048 (3), pp. 301-333 : 311

Choniognathus spinosus n. sp.

( Figures 1A , 6A–F )

Material examined. Holotype: ovigerous female (cl 10.2 mm, pcl 9.5 mm, cw 8.3 mm, bcw 7.3 mm) (MNHN-IU-2008-10297), stn CP3132, Mozambique Channel, 2511’S 3501’E, 101–102 m, coll. MAINBAZA, 10 April 2009.

Diagnosis. Dorsal surface of carapace covered with numerous prominent spines and sharp tubercles; with stiff scattered setae, without dense tomentum which completely covers surface ( Fig. 6A, B ). Pseudorostral spines short, strongly diverging ( Fig. 6A, B ). Supraocular eave broad with concave margin lined with 2 or 3 spines, not completely covering eye ( Fig. 6B ); postocular spine longer than preocular tooth on eave, with short intercalated spine totally filling space between them ( Fig. 6B ). Hepatic spine long, oriented outwards ( Fig. 6B ). Gastric area raised, with numerous granules, with 2 tubercles on top; cardiac area raised, covered by prominent granules, with 5 posterior granules tuberculiform, forming blunt spines ( Fig. 6B, C ); branchial area inflated covered with spines, 2 of them longer ( Fig. 6B ). Posterior carapace margin with 3 rows of long granules like-spines ( Fig. 6B ). Basal antennal article with 4 spines distally, base appressed against infraorbital margin with 2 long spines ( Fig. 6D ). Buccal frame quadrangular, completely covered by third maxillipeds ( Fig. 6D, E ). Third maxilliped with merus and ischium covered by scattered tubercles, merus separated from ischium by suture, structures mobile; anteroexternal angle of merus strongly produced, auriculiform ( Fig. 6D, E ). Cheliped short, dorsal margins and outer surfaces of carpus, merus and chela covered by spines and stiff setae; cutting margins of fingers finely serrulate ( Fig. 6E, F ). Ambulatory legs short, setose ( Fig. 6A ). Pleon with 6 free somites and telson, somite 1 with large median swelling covered by tubercles and granules ( Fig. 6B, C ).

Type locality. Mozambique Channel

Etymology. The name spinosus alludes to the spiny carapace and pereopods of the species.

Remarks. Choniognathus spinosus n. sp. has several unusual features that question its placement in the genus. It differs from the type species, C. reini , in the following characters: the pseudorostral spines are clearly divergent ( Fig. 6A ) (versus directed anteriorly and subparallel in C. reini ; Fig. 7A, C, E ); the supraorbital eave is more expanded with a spinous margin ( Fig. 6A, B ) (versus narrow with the margin entire in C. reini ; Fig. 7A, C, E ); the postocular spine is as long as than the preocular eave tooth, with the intercalated spine totally covering space ( Fig. 6B ) (versus postocular spine is distinctly shorter than the preocular eave tooth with the intercalated spine separated from the eave and postorbital spine by narrow clefts ( Fig. 7A, C, E ); the merus and ischium of the third maxilliped are mobile ( Fig. 6D ) (versus fused in C. reini with the suture very shallow or undiscernible in C. reini ; Fig. 13G, H ); the anteroexternal angle of the merus of the third maxilliped is strongly produced ( Fig. 6D ) (versus lower in C. reini ; Fig. 13G, H ); and the outer surface of the merus, carpus and chela are covered with prominent spines ( Fig. 6A, E, F ) (versus almost smooth in C. reini ; Fig. 7D ). In addition, while C. reini and C. granulosus (cf. Baker 1906: 108) have short ambulatory legs with all the dorsal surfaces of the carapace and pereiopods completely covered by a short dense tomentum ( Fig. 7E ), this is not the case with C. spinosus n. sp., the carapace and pereopods are just covered with short stiff setae, which while dense, do not completely obscure the outline and surfaces like the other two species ( Fig. 1A ).

Figures

FIGURE 1. Colour in life. A, Choniognathus spinosus n. sp., holotype female (cl 9.5 mm, cw 7.3 mm) (MNHN-IU-2008- 10297); B, Kasagia elegans (Stebbing, 1921) comb. nov., male (cl 11.8 mm, cw 7.9 mm) (MNHN-IU-2008-10340); C, K. elegans (Stebbing, 1921) comb. nov., female (cl 11.9 mm, cw 7.4 mm) (MNHN-IU-2010-77); D, K. elegans (Stebbing, 1921) comb. nov., female (cl 7.9 mm, cw 4.9 mm) (MNHN-IU-2008-10339); E, K. sudhakari Padate, Manjebrayakath & Ng, 2019, female, station CP3131, MAINBAZA cruise, Mozambique Channel, specimen not found. Photographs: T.-Y. Chan.

FIGURE 6. Choniognathus spinosus n. sp., holotype female (cl 10.2 mm, cw 8.3 mm) (MNHN-IU-2008-10297), Mozambique. A, overall view; B, dorsal view of carapace (denuded); C, lateral view of cephalothorax; D, ventral view showing antennules, antennae, epistome, buccal cavity and third maxillipeds; E, ventral view of cephalothorax; F, view of right chela and carpus.

FIGURE 7. Choniognathus reini (Balss, 1924).A, B, Holotype of Choniognathus koreensis Rathbun, 1932, female (cl 9.1 mm, cw 6.0 mm) (USNM 48204), Korea; C, D, ovigerous female (cl 6.3 mm, cw 4.0 mm) (ZRC 2020.373), Philippines; E, female (cl 9.1 mm, cw 6.2 mm) (KPM NH 0104599), Japan. A, C, overall view; B, ventral view of cephalothorax; D, outer view of right chela and carpus; E, dorsal view of carapace (frontal parts and right side denuded). A, B, courtesy T. Naruse.

FIGURE 13. A–C, Eurynome longimana Stimpson, 1857. A, B, female, South Africa; C, male (cl 14.0 mm, cl 10.0 mm), South Africa; D–F, Eurynome longimana Stimpson, 1857, male (cl 8.5 mm, cw 5.9 mm) (ZRC 2020.378), Mozambique; G, Choniognathus reini (Balss, 1924), female (cl 9.1 mm, cw 6.0 mm) (USNM 48204), Korea; H, C. reini (Balss, 1924), ovigerous female (cl 6.3 mm, cw 4.0 mm) (ZRC 2020.373), Philippines; I–K, Seiitaoides mirabilis n. sp., holotype male (cl 13.2 mm, cw 7.3 mm) (MNHN-IU-2010-1301), Madagascar.A, dorsal view of carapace and enlarged boletiform tubercle; B, right P5 merus; C, G1; D, I, left G1 (ventral view); E, J, left G1 (dorsal view); F, K, left G2; G, H, left third maxilliped.A–C after Barnard (1950: fig. 12a–c). G, from original figure by T. Naruse. Scale bars = 0.5 mm.