Dorhynchus profundus n. sp.

(Figs. 1A, B, 2–8)

Type material. Holotype: male (cl 11.1 mm, pcl 9.2 mm, cw 8.1 mm, pcw 7.5 mm) (MNHN-IU-2011-2139), stn CP 3741, off coast of Woodlark Island, 9°14’S 152°18’E, 694–766 m, coll. N.O. Alis, BIOPAPUA cruise, S. Samadi & L. Corbari, 694–766 m, coll. 10 October 2010. Paratypes: 1 male (partially crushed, with epicarid isopod in carapace) (cl 11.1 mm, pcl 9.3 mm), 1 female (cl 9.5 mm, pcl 8.6 mm, cw 7.6 mm, pcw 7.2 mm) (MNHN-IU-2011-947), stn CP 3744, off coast of Woodlark Island, 9°17’S 152°17’E, 776–856 m, coll. N.O. Alis, BIOPAPUA cruise, S. Samadi & L. Corbari, coll. 10 October 2010. Other material examined. 1 male (cl 11.8 mm, pcl 10.3 mm, cw 8.2 mm, pcw 8.5 mm) (ZRC 2022.0067), stn DW 4285, Budibudi Island, northern archipelago of Laughlan Island, Solomon Sea, 9°11'S 153°55'E, 380–411 m, coll. MADEEP cruise, 30 April 2014; 1 female (anterior part of carapace broken off) (cl 7.9 mm, pcl 7.0 mm, cw 5.8 mm, pcw 5.6 mm) (MNHN-IU-2015-888), stn CP 4298, south of Woodlark Island, 09°46’S 152°55’E, 474 m, coll. N.O. Alis, MADEEP cruise, 1 May 2014; 1 female (cl 10.3 mm, pcl 8.9 mm, cw 7.9 mm, pcw 7.7 mm) (ZRC 2022.0074, ex MNHN-IU-2015-326), stn DW 4286, northern archipelago of Laughlan Island, Solomon Sea, 09°12’S 153°55’E, 306–365 m, coll. N.O. Alis, MADEEP cruise, 30 April 2014. All specimens from Papua New Guinea.

Comparative material. Dorhynchus rostratus (Sakai, 1932): 1 ovigerous female (cl 5.9 mm, pcl 5.0 mm, cw 4.5 mm, pcw 4.3 mm) (ZRC 2020.0386), stn 2361, Bohol-Sulu Sea, Philippines, 08°53.1’S 123°33.5’E, 516–543 m, coll. MV BFAR, PANGLAO 2005 cruise, 26 May 2005 .

Diagnosis. Carapace with following arrangement of spines on regions – mesogastric: 1 median spine; protogastric: 1 low tubercle; metagastric: 1 large median spine; cardiac: 1 large spine; branchial: 1 short laterally directed spine; lateral carapace margin usually with 3 short spines (Figs. 1A, B, 2A, B, 3A, B, 4A, 6A, B, 7A); pseudorostral spines relatively short, tapering to sharp tip, usually subparallel, tips directed anteriorly, 1 or 2 short accessory spines present on lateral and ventral surfaces (Figs. 1A, B, 2A, B, 3A, B, C, 4A, 8A); supraorbital eave narrow, outer margin straight, preorbital spine long, sharp, postorbital spine directed obliquely (Figs. 3A, B, 4B, 8A); hepatic region with 2 low sharp tubercles; interantennular spine usually just visible in dorsal view (Fig. 3A, 4A); ambulatory legs long, slender, P2 merus 0.85–1.15 times pcl, P3 merus 0.71–1.20 times pcl, all dactyli falciform, each with subterminal vertical spine on ventral margin (Figs. 2A, B, 3C–I); G1 relatively short, C-shaped, distal part with lateral fold, tip rounded (Figs. 5D–F, G, H, 8H–K).

Description of male holotype. Carapace relatively short, pyriform, maximum length 1.37 times maximum carapace width (Figs. 2A, 3A). Dorsal surface with regions well demarcated; epigastric region with longitudinal row of 3 low granules; mesogastric region with 1 median spine; protogastric region with 1 low tubercle, sometimes granuliform; metagastric region with 1 large median spine; cardiac region with 1 large spine; branchial region with 1 short laterally directed spine, lateral margin with 3 short spines; rest of carapace surface smooth, margins with some short curved setae which do not obscure surface or margins; margin of posterolateral margin lined with spinules (Figs. 2A, 3A, 4A, B). Pseudorostral spines relatively short, tapering to sharp tip, subparallel, tips directed anteriorly, separated by distinct V-shaped hiatus; 1 or 2 short accessory spines present on lateral and ventral surfaces (Figs. 2A, 3A, 4B, C, 8A). Supraorbital eave narrow, outer margin straight, preorbital spine long, sharp; no antorbital spine; postorbital spine large, directed obliquely (Figs. 3A, 4B). Eye relatively short, stout; ocular peduncle with prominent projection on anterodistal edge just before cornea peduncle; cornea large, round, with tubercle on upper surface (Figs. 3A, 4A–C, 8A, B). Hepatic region gently inflated, with 2 low sharp tubercles; separated from branchial region by wide concavity (Figs. 2A, 3A). Pterygostomian, sub-hepatic and sub-branchial regions smooth (Fig. 4A, C). Posterior carapace margin gently concave (Fig. 3A). Antennular fossae large, longitudinally ovate; basal article ovate, unarmed (Figs. 4C, 8B). Interantennular spine sharp, well developed, just visible in dorsal view (Fig. 4A, 8B). Basal antennal article fused with epistome, elongate, slender, with shallow longitudinal groove; outer margin lined with low granules, distal margin with 2 low spines; article 3 short, subquadrate, about one-third length of basal article; flagellum long (Fig. 4C, 8A, B). Epistome subquadrate, longer than wide; posterior margin with median triangular lobe, with median fissure, lateral margins weakly sinuous with median fissure (Figs. 4C, 8B, D). Buccal cavity wide, edge with pterygostomial region with angular projection, with 1 short spine on median part of lateral margin.

Third maxilliped ischium longitudinally subovate, submedian sulcus shallow, with sublongitudinal row of spinules on each side, mesial margin uneven, with small pits and granules; merus subquadrate, mesial margin with sharp spines, distal ones longer, with median longitudinal row of spinules; carpus, propodus and dactylus unarmed; exopod long, slender, reaching to distal edge of merus (Figs. 4D, 8E).

Chelipeds slender, long; symmetrical (Figs. 2A, 5A, B). Basis-ischium subtrigonal, outer margin granuliform with sharp spine on distal angle (Fig. 4E). Merus trigonal in cross-section; dorsal margin with 1 subterminal spine and row of smaller sharp tubercles and granules; ventral margin with longer spines on distal part, sharp tubercles on remaining area (Figs. 2A, 5A, B). Carpus with 2 spines on dorsal margin, one subdistal, one subproximal, rest of margin smooth; ventral margin with 2 spines and several spinules (Figs. 2A, 5A). Chela with palm gently inflated; proximal outer surface and dorsal margin with spines, rest of surface smooth; fingers as long as palm, relatively stout; pollex almost straight, dactylus gently curved; cutting margins with low teeth (Figs. 2A, 5A, B).

Ambulatory legs long, slender; surfaces smooth; margins with scattered long and short straight and curved setae; P2 longest, remaining legs gradually decreasing regularly in length, fourth shortest; P2 missing, P3 merus 1.20 times pcl (Fig. 2A). Margins of all meri armed, subdistal part of dorsal margin with low angle, not spinate or dentiform (Fig. 2A). All propodi elongate, slender, unarmed (Fig. 2A). P2 dactylus gently curved, P3–P5 dactyli falciform (most of proximal and median parts slightly curved with distal quarter markedly hooked), each with subterminal vertical spine just before tip, ventral margin of P5 dactylus with 2 or 3 small granules on subproximal part and 5 or 6 evenly spaced sharp tubercles before subterminal spine; ventral margins of P2–P4 with scattered low sharp tubercles (usually 1 or 2), sometimes not clearly visible (Figs. 2A, 3C–E).

Thoracic sternum with surfaces smooth; sternites 1 and 2 fused, sloping gently towards buccal cavity, separated from sternite 3 by ridge; sternites 3 and 4 completely fused, surface gently concave; median part of sternite 4 strongly arched transversely, forming clear convex ridge before sternopleonal cavity, lined with strong sharp tubercles, those on lateral parts larger; sternites 4–8 medially interrupted; tubercle of male pleonal press-button locking mechanism low, rounded, on median part of sternite 5; sternite 7 with prominent bulbous, weakly granulated swelling on median part of posterior area adjacent to sternopleonal cavity; sternite 8 visible when pleon closed (Fig. 4E, F).

Pleon relatively short, somites 1–5 free, somite 6 and telson fused (pleotelson) with only lateral grooves visible (Figs. 4G, 8F); median surface of all somites with numerous small sharp granules, those on pleotelson larger. Somite 1 trapezoidal, broad; somite 2 rectangular; somite 3 widest with median part transversely arched, distinctly convex lateral margins, lateral margins with distinct spinules; somite 4 subtrapezoidal with median part transversely arched, lateral margins distinctly convex; somite 5 subrectangular; pleotelson large, wider than somite 5, telson semicircular, median part swollen with 2 larger sharp tubercles, distal to these are 3 larger spine-tipped tubercles (Figs. 4G, 8F).

G1 relatively short, C-shaped, distal part with lateral fold, tip rounded (Figs. 5C–E, 8H–K). G2 short, without flagellum (Figs. 5F, 8L).

Female and variation. The non-sexual female characters are similar to the male in most aspects, with the chelipeds proportionately shorter and more slender (Figs. 6A, 7A). The female pleon is longitudinally ovate with the surface covered with spinules; with somites 1–5 free and the telson fused with somite 6 without any trace of the suture (Figs. 6A, 8F). The vulvae are relatively large, ovate and positioned in an oblique position close to each other on sternite 6 (Figs. 6C, 7F). There is some variation in the presence and/or number of spines and spinules on the pseudorostrum and orbital areas. The pseudorostrum in the slightly larger paratype male (ZRC 2022.67) has two spinules placed opposite each other on the left spine while on the right spine, they are along different parts of the margin. The paratype female (MNHN-IU-2011-947) has one or two additional spines adjacent to the preorbital spine on the supraorbital eave, with two short spines on the margin between the preorbital and postorbital spines, the base of the left postorbital spine also armed with a short spine (Figs. 6B, 8C). These areas are smooth in the males. The number of spines or sharp tubercles on the hepatic and lateral branchial regions vary. The holotype male has two distinct sharp tubercles on the hepatic region (Fig. 2A) but is very low in another male (Fig. 2B). The holotype male has three short lateral branchial spines on each side (Fig. 2A), but the other male has two low spines on the left and two even lower spines on the right (Fig. 2B), whereas the female has two low spines (Fig. 6B).

For variations and ambulatory legs and shape of pseudorostral spines, see Remarks.

Colour. In life, uniform orange overall (Fig. 1A, B).

Etymology. The species is named for its deep-sea habitat, “ profundus ”, which is Latin for deep and vast.

Remarks. Apart from D. profundus, three species are now known from the Indo-West Pacific: D. ramusculus, D. rostratus and D. thomsoni, of which the last is believed to have a wide distribution, also occurring in the Atlantic. With regards to the relatively shorter rostrum and the ambulatory merus lacking a long subdistal spine on the dorsal margin, D. profundus n. sp. is closest to D. rostratus, a species originally described from Japan (Sakai 1932, 1938, 1976) but also reported from the Kai Islands and Timor Sea (Griffin & Tranter 1986; Takeda et al. 2022).

We have an ovigerous female specimen from the Philippines (ZRC 2020.0386) that we refer to D. rostratus . It agrees well with the original description by Sakai (1932, 1938) except that the pseudorostral spines appear subparallel rather than incurving, although the basal part is somewhat wide (Fig. 9B, C). The dactyli of P2, P3 and P5 are all slender and gently curving with the subterminal spine a short distance from the tip (Fig. 9E, F, H). The P4 dactylus, however, is more falciform (sharply bent distally), but the subterminal spine position is like those of the other legs (Fig. 9G). Significantly, the protogastric spines are prominent (Fig. 9B, C), as described and figured by Sakai (1932, 1938). Its vulvae do not differ significantly from those of D. profundus n. sp. (Fig. 8G). As such, the shape of pseudorostrum may not be a reliable species character, as is the shape of the P4 dactylus.

Dorhynchus profundus n. sp., nevertheless differs from D. rostratus in having the protogastric spines small and low (Figs. 3A, B, 4A, B) (versus relatively large in D. rostratus; Fig. 9B, C; Sakai 1932: text-fig. 3a; Sakai 1938: text-fig. 17; Sakai 1976: text-fig. 90a, b); and the distal part of the P3–P5 dactylus is falciform with the subdistal tooth on the ventral margin adjacent to the tip (Figs. 2A, 3C–E) (versus only P3 and P5 dactylus gently curved with the subdistal tooth on the ventral margin slightly further from the tip in D. rostratus; Fig. 9F, H; Sakai 1932: text-fig. 3c). The G1 of D. rostratus is not known.

Griffin & Tranter (1986: 21) reported of his two male specimens of “ D. rostratus ” from the Kai Islands in Indonesia, that the tips of the pseudorostral spines are incurved and there is a well-developed protogastric spine, but no figure was provided. We are uncertain if his material is D. rostratus s. str. or the new species described here. Takeda et al. (2022: 15) also noted that their female specimen from the Timor Sea is “ D. rostratus ” and that this species has “relatively short, slightly incurved pseudorostral spines”. Their figure, however, shows subparallel and straight pseudorostral spines (Takeda et al. 2022: fig. 5C), but unfortunately, their specimen did not show the ambulatory legs. We believe that Takeda et al.’s (2022) specimen is actually D. profundus n. sp. instead; and like this species, the protogastric spines are also very low (cf. Takeda et al. 2022: fig. 5C).

The series of specimens of D. profundus n. sp. presents some interesting problems with the proportions of the ambulatory legs and structure of the pseudorostral spines. While the holotype male and paratypes from the BIOPAPUA cruise all have relatively longer ambulatory legs (Figs. 2A, 3C–E) (P2 merus 1.12 times pcl, P3 merus 0.97–1.20 times pcl), the specimens from the MADEEP cruise have more variable proportions (P2 merus 0.89–1.15 times pcl, P3 merus 0.86–0.94 times pcl) (Figs. 2B, 3F–I), with those of one female (ZRC 2022.0074), especially short (P2 merus 0.85 times pcl, P3 merus 0.71 times pcl) (Fig. 7A, B, E). The significance of this variation is not known. They agree in almost all other characters; with the G1s of the long-legged types and the shorter-legged male (ZRC 2022.0067) nearly identical (Fig. 5C–E, G, H). There are also no species-level differences in their carapace, chelipeds and ambulatory leg armature. As such, we treat them as conspecific. As noted above, whether the pseudorostral spines are gently inward curving or subparallel is probably not significant at the species level and probably the result of intraspecific variation. We note is that in one paratype female (MNHN-IU-2011-947), while the tips of the pseudorostral spines are broken, the base of the spines is somewhat wider than the holotype male and the intact part of the spine appears to be slightly curving inwards (Fig. 6B).

This female with shortest legs (ZRC 2022.0074) is also unusual in that the base of the pseudorostral spines is swollen with the spines curving inwards distally (Fig. 7A, B, E), similar to that described and figured for D. rostratus by Sakai (1932, 1938). The vulvae of this female (ZRC 2022.0074) differ somewhat from that of the paratype female in that the raised portion of sternite 6 on which the vulva is placed is slightly more pronounced with the opening directed somewhat more laterally (Fig. 7F) (versus sternite 6 surface slightly lower and the vulvae open more vertically; Fig. 6C), although this can be accounted for by normal variation. The protogastric spines are, however, are low like those of the other Papua New Guinea specimens (Fig. 7A, C). That being said, the carapace of this shorter-legged female appears somewhat deformed, and the right antenna is also missing with the features there anomalous (Fig. 7C) and as such some of the above observed characters may be due to damage and/or regrowth. All the ambulatory legs, however, are relatively shorter than typical specimens, not just a few legs (Fig. 7A, B). We provisionally refer this specimen to D. profundus n. sp. for the time being.

The type series of D. profundus n. sp. was from depths of 694–856 m , with the non-type material from the other cruises found between 306– 474 m. Whether this depth occurrence is associated with the observed morphological differences with the leg proportions (see above) cannot be ascertained. Dorhynchus rostratus was described from a depth of 183–366 m , with Suzuki & Kurata (1967) stating that their specimen was from about 150 m. The present specimen from the Philippines was from relatively deeper water at 516– 543 m.