Hyastenus, White, 1847

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, Zootaxa 5318 (1), pp. 1-44 : 38-41

Hyastenus ? borradailei (Rathbun, 1907)

( Figs. 29A–F , 30A–D )

Material examined. 1 male (pcl 7.1 mm, pcw 5.0 mm) (MNHN-IU-2015-241), stn DW4313, North Normanby Island, Solomon Sea , 09°49’S 151°34’E, 105–157 m, coll. MADEEP, 3 May 2014 ; 1 male (pcl 6.3 mm, pcw 3.8 mm) (MNHN-IU-2015-911), stn DW4488, New Ireland, 02°25’S 149°57’E, 173–179 m, coll. KAVIENG, 6 September 2014 .

Diagnosis. Carapace pyriform ( Fig. 29A, D ). Pseudorostral spines slender, long, almost as long as maximum carapace length (excluding pseudorostral spines), diverging ( Fig. 29A, D ). Supraorbital eave fused to carapace, forms weak lobe in some; preorbital angle sharp, antorbital angle weak or blunt; postorbital lobe cup-like ( Fig. 29C, F ). Carapace regions defined; gastric region with 2 mesogastric granules in row on slightly swollen gastric region ( Fig. 29A, D ), 4 protogastric granules in transverse row; cardiac region slightly swollen; lateral margin of carapace with granules; weak lateral branchial spine ( Fig. 29A, D ). Antennal flagellum shorter than pseudorostral spines. Basal antennal article longer than broad, distal angle sharp to relatively blunt; outer margin slightly constricted medially. Pterygostomial region with 2 granules on outer margin, with first granule larger ( Fig. 29B, E ). Cheliped slender; propodus longer than fingers; carpus with 2 or 3 granules on outer margin (cf. Borradaile 1900 b) or 5 or 6 granules on outer margin ( Fig. 29A, D ); merus with distal spine ( Fig. 29A, D ). Ambulatory legs slender; dactylus with spines on inner margin; P2 longest ( Fig. 29A, D ). Male thoracic sternum slightly depressed anteriorly; sternites 3, 4 narrow, lateral margin slightly constricted. Male pleon triangular, telson triangular ( Fig. 29B, E ). G1 straight, slightly twisted on distal half, with sharp distal tip ( Fig. 30A–D ).

Remarks. Hyastenus borradailei (Rathbun, 1907) is a replacement name for Hyastenus elegans var. tenuicornis Borradaile, 1900 , the latter being a homonym of Hyastenus (Chorilia) tenuicornis Pocock, 1890 . Hyastenus elegans Miers, 1886 s. str. is now a junior synonym of Naxioides robillardi (Miers, 1882) (see Poupin 1995: 89).

Hyastenus borradailei (as Hyastenus elegans var. tenucornis ) was described from two males and one female specimen collected from Rotuma in the western Pacific ( Borradaile 1900: 574). Borradaile (1900) compared his specimens to the type of Naxioides robillardi (Miers, 1882) and noted three main differences between the two species: the pseudorostral spines of H. borradailei are more slender and diverge more strongly at the base, the carapace granules are relatively larger and rounded, and the placements of gastric granules are different ( Borradaile 1900: 574, pl. 40 fig. 2). The specimen, as figured by Borradaile (1900: pl. 40 fig. 2), closely resembles Naxioides but it has no obvious supraorbital lobe, a characteristic of Hyastenus ; and there is also no indication of an additional small spine on the pseudorostral spine, a genus character for Naxioides (cf. Poupin 1995). As such, it should be retained in Hyastenus until the type can be re-examined.

Subsequent reports of “ Hyastenus borradailei ” by Sakai (1938, 1976) (from Japan) and Griffin & Tranter (1986 a) (from Timor, Indonesian Moluccas and Australia) are uncertain. While their specimens superficially match the description and figures of Borradaile (1900), they differ from the type figures in that they possess a distinct supraorbital lobe (cf. Griffin & Tranter 1986: fig. 38g). Their pseudorostral spines are also entire, without any trace of accessory spines, and as such, are typical Hyastenus in all aspects. The differences observed may indicate we are dealing with two different species, but no decisions should be made until the types can be re-examined.

The specimens collected from Papua New Guinea resemble those reported by Griffin & Tranter (1986) and as such, are provisionally referred to Hyastenus borradailei (Rathbun, 1907) .

Distribution. Hyastenus borradailei has previously been reported from Fiji (Rotuma), Tuvalu ( Ellice Islands), Western Australia and Queensland, Timor, Moluccas, Philippines (Mindanao), Amirante Islands, Mauritius (Cargados Carajos) (cf. Ward 1941; Sakai 1976; Griffin & Tranter 1986), and now Papua New Guinea.

Figures

FIGURE 29. Hyastenus? borradailei (Rathbun, 1907), A–C, male (pcl 6.3 mm, pcw 3.8 mm) (MNHN-IU-2015-911), New Ireland; D–F, male (pcl 7.1 mm pcw 5.0 mm) (MNHN-IU-2015-241), North Normanby Island.A, D, overall dorsal view; B, E, overall ventral view; C, F, lateral view.

FIGURE 30. Hyastenus? borradailei (Rathbun, 1907), left G1. A, B, male (pcl 6.3 mm, pcw 3.8 mm) (MNHN-IU-2015-911), New Ireland; C, D, male (pcl 7.1 mm pcw 5.0 mm) (MNHN-IU-2015-241), North Normanby Island. A, C, ventral view; B D, dorsal view. Scales: 1.0 mm.