Homologenus exilis, Ng & Forges, 2017

Ng, Peter K. L. & Forges, Bertrand Richer de, 2017, On a collection of Homolidae from the South China Sea, with descriptions of two new species of Homologenus A. Milne-Edwards, in Henderson, 1888, and the identities of Homologenus malayensis Ihle, 1912, and Lamoha superciliosa (Wood-Mason, in Wood-Mason & Alcock, 1891), Raffles Bulletin of Zoology 65, pp. 243-268 : 255-258

publication ID	https://doi.org/ 10.5281/zenodo.5356049
publication LSID	lsid:zoobank.org:pub:CC246EF9-E704-4DDC-BD25-61B6102A382F
persistent identifier	https://treatment.plazi.org/id/63A291D4-8549-4CEE-BAB7-33F2422648AE
taxon LSID	lsid:zoobank.org:act:63A291D4-8549-4CEE-BAB7-33F2422648AE
treatment provided by	Valdenar
scientific name	Homologenus exilis
status	sp. nov.

Treatment

Homologenus exilis View in CoL n. sp.

( Figs. 14 View Fig , 15 View Fig , 18D–F View Fig , 19A–H View Fig , 20C–E View Fig , 21D–F View Fig , 22A–C View Fig )

? Homologenus malayensis View in CoL – Nagai, 1994: 50, pl. 1, fig. 3. (not

Homologenus malayensis Ihle, 1912 View in CoL )

Material examined. Holotype: ovigerous female (13.5 × 10.4 mm) ( NTOU), station CP 4132, southwest of Tungsha Island , 20°11.46′N 116°20.14′E – 20°07.26′N 116°21.51′E, GoogleMaps

957–988 m, Taiwan, South China Sea , sandy bottom, trawl, coll. ZHONGSHA 2015 Cruise, 22 July 2015. Paratypes: 1 male (10.2 × 7.4 mm) ( ZRC 2016.0568 View Materials ), same data as holotype. – 1 female (15.1 × 11.4 mm) ( ZRC 2016.0569 View Materials ), station CP 4133, southwest of Tungsha Island, 20°04.51′N 116°22.37′E – 19°58.89′N 116°24.28′E GoogleMaps , 999–1070 m, Taiwan, South China Sea , sandy bottom with thin stalked sponges, trawl, coll. ZHONGSHA 2015 Cruise, 22 July 2015. – 1 male (11.4 × 9.6 mm) ( ZRC 2016.0570 View Materials ), station CST 11, muddy bottom with numerous branching corals, Formosa Ridge, Taiwan, 22°8.83′N 119°15.68′E – 22°6.46′N 119°17.43′E GoogleMaps , 1176–1318 m, coll. 27 April 2016.

Diagnosis. Small species, covered with scattered long and short setae ( Fig. 14 View Fig ). Carapace longer than wide; male carapace longitudinally ovate; anterior half of female carapace slightly narrower than posterior half; surface of carapace granulous; gastro-cardiac and branchio-cardiac grooves well marked; with long sharp median gastric spine and 2 short epigastric spines; short spine at angle of buccal cavity; line of prominent granules marking border of pterygostomian region ( Figs. 14 View Fig , 15A View Fig , 18D–F View Fig ). Rostrum very long, curved, sharp, with 2 short accessory pseudorostral spines pointing anteriorly ( Figs. 14 View Fig , 15A, B View Fig , 18D–F View Fig ). Strong pseudorostral spines in supra-ocular position gently curving laterally outwards; supraorbital margin with short spine ( Figs. 14 View Fig , 15A, B View Fig , 18D–F View Fig ). Basal antennal spine strong ( Fig. 15A View Fig ). Subhepatic spine slender ( Fig. 15A View Fig ). Anterolateral spine long, sharp, pointing obliquely outwards ( Figs. 14 View Fig , 15A View Fig , 18D–F View Fig ). Anteroexternal angle of merus of third maxilliped with 2 sharp curved spines ( Fig. 15C View Fig ). Female cheliped short; chela slightly inflated: chela with 6 small spines on ventral margin and 3 spines on dorsal margin; fingers long, slender, curved inwards; carpus with 3 long spines on external face; merus with 5 strong spines on outer margin and 6 spines on inner margin ( Fig. 15D, E View Fig ). Male cheliped short; chela inflated, triangular in cross-section, fingers closely appressed when closed; margins of merus spinose; carpus with 4 prominent spines; dorsal margin of chela with 4 spines, ventral margin with 4 spines ( Fig. 21F View Fig ). Ambulatory legs (P2–P4) very long, slender; P 5 in dorsal position, merus without spines, reaching base of anterolateral spine when folded on carapace, dactylus long, slender, curved, sharp, touching proximal spine of propodus, forming pseudochela ( Figs. 14 View Fig , 19D, H View Fig , 20C–E View Fig ); female: P2 merus with 4 or 5 spines on dorsal margin, outer surface with 2 spines, ventral margin with 6 spinules; P3 merus with 5 long straight spines on dorsal margin, outer surface with 1 short spine, ventral margin with 8 spines and spinules; P4 merus with 4 or 5 spines on dorsal margin, outer surface with 1 spinule, ventral margin with 5 or 6 spines ( Figs. 14A View Fig , 19A–C View Fig ); male: P2 merus with 3 or 4 spines on dorsal margin, outer surface with 2 spines, ventral margin with 6 spinules; P3 merus with 4 long straight spines on dorsal margin, outer surface with 2 spinules, ventral margin with 5 spines and spinules; P4 merus with 3 spines on dorsal margin, outer surface with 1 spinule, ventral margin with 3 spines ( Figs. 14B View Fig , 19E–G View Fig ); P2–P4 propodus very long, dactylus very long, falciform ( Fig. 14 View Fig ). Armature of pleonal somites as follows: female somite 2 with 1 median spine, somite 3 with 4 low spines, somite 4 with 4 very low spines, somite 5 with 4 very low spines, telson, somites 1, 5 and 6 unarmed ( Fig. 15F View Fig ); male somite 2 with 1 median spine, somite 3 with 5 low spines, somite 4 with 4 low spines, somite 5 with 4 low spines, telson, somites 1 and 6 unarmed ( Fig. 21D, E View Fig ). G1 relatively stout, distal part subtruncate ( Fig. 22A, B View Fig ).

Etymology. From the Latin “ exilis ” meaning “thin or slender”, alluding to the relatively long ambulatory legs of the species when compared to the other new species, H. brevipes . Used as a noun in apposition.

Remarks. The two new species described here are superficially similar and resemble H. malayensis Ihle, 1912 , and were referred to this taxon initially. They also resemble H. donghaiensis Chen, 1986 (see Ng & Chen, 1999). The most notable difference is the observation that in H. malayensis , the ventral margin of the merus of the P4 is completely unarmed ( Figs. 8B View Fig , 12G, K View Fig ) whereas in the two new species, there are two distinct spines on the ventral margin ( Fig. 19C, G, K, O View Fig ). In addition, H. malayensis also differs from H. exilis n. sp. and H. brevipes n. sp. in having a proportionately longer male telson ( Fig. 21A View Fig vs. Fig. 21D, G View Fig ), and the G1 is less prominently curved ( Fig. 12C View Fig vs. Fig. 22A, D View Fig ). Compared to H. donghaiensis , the two new species have more longitudinally ovate and more pyriform carapaces ( Fig. 18D–I View Fig ) (carapace distinctly more rectangular in H. donghaiensis , Figs. 13A View Fig , 18C View Fig ); the carpus of the cheliped has relatively weaker spines ( Figs. 15D View Fig , 17D View Fig ) (very strong and long in H. donghaiensis , Fig. 13A, B View Fig ); and the ventral margin of the P4 merus is armed with spines ( Fig. 19C, G, K, O View Fig ) (unarmed in H. donghaiensis , Fig. 13A–C View Fig ).

In addition to the above differences, H. exilis differs from H. malayensis in that the anteroexternal angle of the merus of the third maxilliped has two spines ( Fig. 15C View Fig ) (usually with only 1 spine in H. malayensis , Figs. 8G View Fig , 12A View Fig ; Guinot & Richer de Forges, 1995: fig. 65B). The proportions of their ambulatory legs are similar (cf. Figs. 9 View Fig , 10, 12E–G, I–K View Fig , 14 View Fig , 19A–C, E–G View Fig ).

With regards to the very long P2–P4, H. exilis superficially resembles H. donghaiensis Chen, 1986 . However, H. exilis can be easily distinguished by its more pyriform male carapace ( Figs. 14 View Fig , 18D–F View Fig ) (more rectangular with the lateral margins subparallel in H. donghaiensis , Figs. 13A View Fig , 18C View Fig ; Ng & Chen, 1986: fig. 3a); the anteroexternal angle of the merus of the third maxilliped has two spines ( Fig. 15C View Fig ) (only one spine in H. donghaiensis , cf. Ng & Chen, 1999: fig. 3f); the spines on the margins of the carpus of the cheliped are relatively weak ( Fig. 15D View Fig ) (carpal spines prominent and strong in H. donghaiensis , Fig. 13A, B View Fig ; Ng & Chen, 1999: fig. 3b); the P2–P4 are proportionately shorter ( Figs. 14 View Fig , 19A–C, E–G View Fig ) (P2–P4 distinctly longer in H. donghaiensis , Fig. 13A View Fig ; Ng & Chen, 1999: fig. 3d); the P5 merus is relatively shorter ( Figs. 14 View Fig , 19D, H View Fig ) (P5 merus distinctly longer in H. donghaiensis , Fig. 13A View Fig ; Ng & Chen, 1999: fig. 3e); and the P5 dactylus is proportionately longer, extending beyond the subproximal propodal spine ( Figs. 14 View Fig , 20C–E View Fig ) (P5 dactylus relatively shorter, not reaching the subproximal propodal spine in H. donghaiensis , Fig. 13A, B View Fig ; Ng & Chen, 1999: fig. 3e). The distal part of the G1 of H. exilis also appears to be slightly more truncate and stouter ( Fig. 22A, B View Fig ) compared to that of H. donghaiensis (cf. Ng & Chen, 1999: fig. 3h).

Homologenus exilis different from H. brevipes by the proportionately longer rostrum ( Figs. 14 View Fig , 15B View Fig , 18D, E View Fig ) (distinctly shorter in H. brevipes , Figs. 16 View Fig , 17B View Fig , 18G–I View Fig ); the pseudorostral spines are gently curving laterally ( Fig. 18D–F View Fig ) (spines straight and directed obliquely laterally in H. brevipes , Fig. 18G–I View Fig ); the proportionately longer median gastric spine ( Fig. 15A View Fig ) (proportionately shorter in H. brevipes , Fig. 17A View Fig ); the anteroexternal angle of the merus of the third maxilliped has two spines ( Fig. 15C View Fig ) (only one spine in H. brevipes , Fig. 17C View Fig ); the distinctly longer P2–P4 ( Figs. 14 View Fig , 19A–C, E–G View Fig ) (relatively shorter P2–P 4 in H. brevipes , Figs. 16 View Fig , 19I–K, M–O View Fig ); the P5 merus, when folded, reaches to the base of the anterolateral spine ( Fig. 14 View Fig ) (not reaching base of anterolateral spine in H. brevipes , Fig. 16 View Fig ); and the P5 dactylus is relatively more slender and longer ( Fig. 20C–E View Fig ) (P5 dactylus relatively shorter and stouter in H. brevipes , Fig. 20F–H View Fig ). The distal part of the G1 of H. exilis ( Fig. 22A, B View Fig ) is also relatively more truncate and stouter than that of H. brevipes ( Fig. 22D, E View Fig ). The anterolateral spines of H. exilis are also relatively longer and directed more laterally ( Fig. 18D–F View Fig ) compared to those of H. brevipes which are shorter and directed more anteriorly ( Fig. 18G–I View Fig ). In general, in most specimens, the carapace and P2–P 4 in H. brevipes are more setose (e.g., Figs. 16 View Fig , 19I–P View Fig ) compared to the condition in H. exilis (e.g., Figs. 14 View Fig , 19A–H View Fig ).

The Japanese specimen from Wakayama Prefecture figured by Nagai (1994: pl. 1 fig. 3) as “ Homologenus malayensis ” appears to be closer to H. exilis on the basis of its relatively longer rostrum and ambulatory legs.