Homologenus A. Milne-Edwards

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 : 251

Homologenus A. Milne-Edwards , in Henderson, 1888

Remarks. Homologenus is a genus composed of small species living in deep waters, often greater than 1000 m, on muddy or sandy substrates. Eleven species are known from the Atlantic and the Pacific Oceans: H. rostratus (A. Milne-Edwards, 1880) (Caribbean Islands) ; H. braueri Doflein, 1904 (Somalian coast); H. malayensis Ihle, 1912 ( Indonesia) ; H. broussei Guinot & Richer de Forges, 1981 ( French Polynesia); H. asper Zarenkov , in Zarenkov & Khodkina, 1983 (East Pacific Marcus-Necker seamounts); H. donghaiensis Chen, 1986 (East China Sea); H. orientalis Zarenkov, 1990 (East Pacific seamounts); H. levii Guinot & Richer de Forges, 1995 ( New Caledonia); H. wallis Guinot & Richer de Forges, 1995 ( Wallis and Futuna Islands); H. boucheti Guinot & Richer de Forges, 1995 (Madere, eastern Atlantic); and H. namakae Ng, 2016 (Hawaii) . Two new species from the South China Sea ( H. exilis n. sp. and H. brevipes n. sp.) allied to H. malayensis and H. donghaiensis are described below.

The two new species of Homologenus described here are represented by both sexes, and allow us to observe some sexually dimorphic features. In females, the armature on P2–P4 ( Figs. 9A , 10A, 12E–G , 16A, B , 19A–C, I–K ) is stronger and more prominent than in males ( Figs. 9B , 10B, 12I–K , 16C , 19E–G, M–O ). The spines on the pleonal somites 2–5 in males ( Fig. 21A, B, D, E, G, H ), however, are always stronger and more prominent than in females ( Figs. 11F , 15F , 17F ).

Of interest is that all specimens of H. brevipes have been collected from deep waters just off the narrow continental shelf of eastern and southeastern Taiwan; whilst those of H. exilis are from off Tungsha Island, some 400 km westsouthwest of Taiwan.

Figures

Fig. 9. Homologenus malayensis Ihle, 1912, overall habitus. A, lectotype female (15.5 × 9.8 mm) (NNM ZMA DE 102.967), station 122, northern Sulawesi, 1°58.5′N 125°00.5′E, Indonesia, 1264–1165 m, coll. SIBOGA Expedition, Weber, 17 July 1899; B, paralectotype (11.3 × 6.1 mm) (NNM ZMA DE 102.967), same data as lectotype. Photographs courtesy of Charles Fransen.

Fig. 12. Homologenus malayensis Ihle, 1912. A–D, I–L, male (carapace width 6.2 mm, rostrum damaged) (ZRC 2016.0194), Papua New Guinea; E–H, female (16.0 × 13.9 mm) (ZRC 2016.0196), Papua New Guinea. A, left third maxilliped; B, dorsal view of right cheliped carpus; C, left G1; D, left G2; E–L, female left P2–P5 merus, respectively; I–L, male left P2–P5, respectively. Scales: C, D = 0.5 mm; E–L = 5.0 mm.

Fig. 16. Homologenus brevipes n. sp., overall habitus. A, holotype ovigerous female (15.0 × 10.7 mm) (NTOU), Taiwan; B, paratype ovigerous female (15.4 × 13.5 mm) (ZRC 2016.0572), Taiwan; C, paratype male (7.6 × 5.9 mm) (ZRC 2016.0574), Taiwan.

Fig. 19. Left P2–P5 merus of Homologenus species. A–D, H. exilis n. sp., holotype ovigerous female (13.5 × 10.4 mm) (NTOU), South China Sea; E–H, H. exilis n. sp., paratype male (10.2 × 7.4 mm) (ZRC 2016.0568), South China Sea; I–L, H. brevipes n. sp., holotype ovigerous female (15.0 × 10.7 mm) (NTOU), Taiwan; M–P, H. brevipes n. sp., paratype male (7.6 × 5.9 mm) (ZRC 2016.0574), Taiwan. A–D, I–L, female left P2–P5 merus, respectively; E–H, M–P, male left P2–P5, respectively. Scales = 5.0 mm.

Fig. 21. A–C, Homologenus malayensis Ihle, 1912, male (carapace width 6.2 mm, rostrum damaged) (ZRC 2016.0194), Papua New Guinea; D–F, H. exilis n. sp., paratype male (10.2 × 7.4 mm) (ZRC 2016.0568), South China Sea; G–I, H. brevipes n. sp., paratype male (7.6 × 5.9 mm) (ZRC 2016.0574), Taiwan. A, D, G, telson and pleonal somites 5 and 6; B, E, H, pleonal somites 2–6; C, F, I, outer view of left chela.

Fig. 11. Homologenus malayensis Ihle, 1912, female (16.0 × 13.9 mm) (ZRC 2016.0196), Papua New Guinea. A, frontal view of cephalothorax; B, rostrum, pseudorostrum and orbit; C, left third maxilliped; D, dorsal view of right cheliped carpus; E, outer view of left chela; F, posterior carapace margin and male pleonal somites 1.

Fig. 15.Homologenus exilis n. sp., holotype ovigerous female (13.5 × 10.4 mm) (NTOU), South China Sea. A, frontal view of cephalothorax; B, rostrum, pseudorostrum and orbit; C, left third maxilliped; D, dorsal view of right cheliped carpus; E, outer view of left chela; F, posterior carapace margin and male pleonal somites 1–3.

Fig. 17. Homologenus brevipes n. sp., holotype ovigerous female (15.0 × 10.7 mm) (NTOU), Taiwan. A, frontal view of cephalothorax; B, rostrum, pseudorostrum and orbit; C, left third maxilliped; D, dorsal view of right cheliped carpus; E, outer view of left chela; F, posterior carapace margin and male pleonal somites 1–3.