Grypachaeus tenuicollis Takeda 1978
Creators: name: Ng, Peter K. L.
name: Forges, Bertrand Richer De
name: Lee, Bee Yan
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Inachidae
Grypachaeus
Grypachaeus tenuicollis

description: Grypachaeus aff. tenuicollis Takeda, 1978
(Figs. 1E, F, 23, 24)
Material examined. 1 male (rostrum broken, pcl 10.1 mm, cw 6.0 mm, pcw 5.0 mm) (ZRC 2022.0075, ex MNHN- IU-2014-18677), stn 4502, New Ireland, Papua New Guinea, 02°32’S 150°44’E, 193–206 m, coll. N.O. Alis, KAVIENG 2014 expedition, 7 September 2014; 1 female (cl 7.6 mm, pcl 7.1 mm, cw 4.3 mm, pcw 4.0 mm) (ZRC 2002.505), stn V4698-107, East China Sea, 162 m, coll. cruise by Institute of Oceanography, Academia Sinica, China, 6 June 1975; 1 ovigerous female (cl 8.1 mm, pcl 7.2 mm, cw 4.9 mm, pcw 4.3 mm) (ZRC 2022.0077), stn T1, on mud with sponges, Bolod, Panglao Island, Bohol, Philippines, 9°32.4'N 123°47.3'E, 83–102 m, coll. PANGLAO 2004 Expedition, 30 May 2004; 1 ovigerous female (cl 11.6 mm, pcl 10.4 mm, cw 6.5 mm, pcw 5.8 mm) (ZRC 2012.1160), stn AT44, Urèlapa island, Vanuatu, coll. SANTO 2006 expedition, 29 September 2006.
Remarks. The present specimen from Papua New Guinea is problematic because it is clearly neither G. hyalinus (Alcock & Anderson, 1894) nor G. tenuicollis Takeda, 1978. Grypachaeus hyalinus has a prominently shorter carapace with the “neck” (frontal and epigastric regions) shorter, the meso-, metagastric branchial regions are distinctly wider and the ambulatory legs are relatively short (cf. Alcock & Anderson 1896: pl. 17 fig. 3). Griffin (1974) reported on specimens from Mombasa and the Gulf of Aden and figured a G1 that is relatively straighter with the small dorsal fold closer to the tip (Griffin 1974: fig. 1e, f) (versus gently curved with the dorsal fold further from the tip in the present specimen; Fig. 23C). Griffin (1976: 190) also reported G. hyalinus from the Philippines but without any figures. Grypachaeus tenuicollis is a very distinctive species, with a very slender carapace, the “neck” is long and slender, the pseudorostral spines are relatively long and slender, and there is only one laterally directed spine on the hepatic region, the ambulatory legs are proportionately shorter, the G1 more slender and C-shaped with the distal part turned sharply at almost 90º (cf. Takeda 1978: figs. 1, 2, 7, 9–11) (versus carapace less elongate, the branchial regions are relatively wider, the ambulatory legs are proportionately longer, and the G1 is proportionately stouter less curved with the distal part tapering; Fig. 23A–C). The differences here suggest that the species on hand is new, but the present specimen is too incomplete to formally describe for now: its pseudorostrum is broken off, and both P5 are missing. There is a second specimen, a female (MNHN-IU-2015-85; stn DW4313, north of Normanby island, southeast of Entrecasteaux Archipelago, Papua New Guinea, 09°49’S 151°34’E, 105–175 m, coll. N.O. Alis, MADEEP cruise, 3 May 2014) (Fig. 1E) that was photographed but we have not been able to examine the specimen. It appears to agree very well with the male examined here and it still has the left P5 intact, but its pseudorostrum is also broken off.
We have on hand one adult female specimen from Vanuatu (ZRC 2012.1160) that may be conspecific with the Papua New Guinea specimens, having the same carapace and “neck” proportions, the two hepatic spines directed obliquely, and the meso-, metagastric and branchial regions more quadrate in shape (Fig. 24F). This Vanuatu specimen has an intact pseudorostral spine and this is long (Fig. 24F). Its ambulatory legs, however, are proportionately shorter (Fig. 24C); but this may be due to sexual dimorphism.
We also have two other specimens from the East China Sea (ZRC 2002.505) and Philippines (ZRC 2022.0077), and neither are G. hyalinus. Compared to G. tenuicollis, they are still distinctly wider at the gastric and branchial regions, the “neck” is distinctly shorter, the pseudorostral spines are relatively short, and there are two lateral spines on the hepatic region with the anterior one obliquely directed (Fig. 24D, E). As the two specimens are females, it is difficult to ascertain whether these are the result of sexual dimorphism, although it seems unlikely; the male and female specimens from Papua New Guinea do not show such prominent differences. Their short pseudorostral armature is different from those of G. tenuicollis s. str. and the Vanuatu specimen (pseudorostral spines long) and indicates this character is not associated with sexual dimorphism as all are females.
description: Published as part of Ng, Peter K. L., Forges, Bertrand Richer De & Lee, Bee Yan, 2023, New and rare deep-sea majoid crabs (Crustacea: Brachyura) from Papua New Guinea, pp. 1-44 in Zootaxa 5318 (1) on pages 30-32, DOI: 10.11646/zootaxa.5318.1.1, http://zenodo.org/record/8158079