Homolodromia hakuhoae Takeda, Ohtsuchi & Komatsu, 2021, sp. nov.

(Figs. 6–8)

Material examined. RV Hakuhō Maru KH-72-1 cruise, sta. 08 (Sulu Sea; 08°44.6′N, 119°05.4′E – 08°44.8′N, 119°06.2′E; 2,030 – 2,030 m deep); 3 m beam trawl; 25 May, 1972; ˂ (ovig.) holotype, NSMT-Cr 28967.

Measurements. CB 12.8 mm; CL in median line, 17.3 mm; length of rostrum, 2.8 mm; length of first ambulatory leg, 67.0 mm; diameter of egg, 2.0– 2.1 mm.

Diagnosis. Carapace, chelipeds and ambulatory legs thickly covered with short stiff setae; carapace narrow, convex dorsally, weakly widening posteriorly, with surface smooth. Front with deep U-shaped excavation, with a pair of strong, spiniform teeth directed forwards. External orbital tooth as long as, but narrower than frontal tooth, directed obliquely outward. Chelipeds slender, with weakly widening palm; fingers deeply excavated along grasping edges, fixed finger with bifid tip. Ambulatory legs long, cylindrical. Subchelae at tips of last 2 legs armed with 2 strong spines at distal part of the upper margin and 4 longer spines at truncated part of distal extension of palm.

Description of holotype (Ovigerous female). Carapace, chelipeds and ambulatory legs uniformly and thickly covered with short, stiff setae, without long setae (Fig. 6A–B). Carapace (Fig. 6C) narrowly oblong, strongly convex dorsally, weakly widening posteriorly, widest at posterior parts of branchial regions of both sides; carapace dorsal areolation obscured by setae, but surface (after denudation) smooth, without granules or spinules, roughly divided into three parts: 1) anterior part including protogastric and hepatic regions in front of a pair of median small pits side by side at boundary between meso- and metagastric regions, 2) median part including metagastric, cardiac and mesobranchial regions, and 3) posterior part including intestinal and metabranchial regions; in dorsal view, a flattened hepatic swelling lateral to the buccal flame. Frontal teeth strong, tuberculate, tapering to sharp tip (Fig. 6C) separated by deep U-shaped sinus. Each supraorbital margin (Fig. 6C) provided with 2 granules at medially, followed by obliquely-outward directed spiniform tooth at external angle. Eyestalk (Fig. 7D) short, cornea distinct, mostly obscured by setae. Antennal flagellum (Fig. 6A) slightly longer than carapace length, each segment provided with some longish setae; basal segment armed with strong spine at distal part of outer margin.

Third maxilliped (Fig. 7A) long, rather pediform, with quadrate ischium and merus; outer margin of merus armed with some spinules; exopod tapers, not reaching merus distal margin.

Pleon (Fig. 7E) seven-segmented, pleomeres 1–6 and telson strongly developed; surfaces of all pleomeres and telson smooth, covered with setae, longitudinally convex along median line; telson subequal in length to pleomeres 1–6 combined.

Chelipeds mostly subcylindrical, palm (Fig. 7C) only slightly widening distally, but not inflated at all; upper inner margin of movable finger strongly crested as a longitudinal edge, both of lower margins entire, resembling bird beak; immovable finger deeply excavated to receive movable finger, bifid at tip and toothed along inner margin (Fig. 7A–B).

Ambulatory legs (Fig. 6A) cylindrical, remarkably long, first leg ca 3.8 times as long as carapace. Last 2 pairs subdorsal as usual, about half as long as anterior 2 pairs; subchela of each pair similar in shape and armature, with 2 strong spines at distal part of propodus upper margin, 4 longer spines at truncated part of distal extension of propodus (Fig. 8).

Etymology. Named after the RV Hakuhō Maru of the Ocean Research Institute, University of Tokyo.

Remarks. The genus Homolodromia was extensively studied by Guinot (1995) who distinguished five species in the genus (H. paradoxa A. Milne-Edwards, 1880 and H. monstrosa Martin, Christiansen and Trautwein, 2001 from the West Atlantic; H. robertsi Garth, 1973 from the East Pacific; H. kai Guinot, 1993 from the West and South Pacific; H. bouvieri Doflein, 1904 from the western Indian Ocean). Recently, Padate et al. (2020) described the sixth species, H. rajeevani from the eastern Arabian Sea and the southwestern Bay of Bengal. All of the six species are deep-water inhabitants, with bathymetric range, 375–914 m (H. paradoxa), 631– 814 m (H. monstrosa), 560–880 m (H. robertsi), 680–850 m (H. kai), 492–960 m (H. bouvieri), and 645–957 m (H. rajeevani).

Padate et al. (2020) prepared the key to the six species based on Guinot (1995) and Tavares and Lemaitre (2014). Following the key, the present new species, H. hakuhoae, is keyed out as follows: 1) lPropodal thumbs of P4–P5 pseudochelae terminating in more than 2 curved distal spines. Pollex of cheliped without occlusal notch; dactylus without proximal elevation,z differing from H. rajeevani and H. bouvieri. 2) lCarapace and pereopods smooth, carpus of cheliped bearing short disto-lateral spine; anterolateral teeth oriented obliquely,z differing from H. robertsi. 3) lCarapace and appendages covered with short, stiff setae; pseudo-rostral horns separated by V-shaped gap,z differing from H. kai. 5) The remaining two species, H. paradoxa and H. monstrosa are differentiated in the characters that lMales having distinct supraorbital spine; antennal spine bifurcated. Mature females with relatively short P5, P5 meri not reaching the level of gastric pits on carapace in longitudinal position in H. paradoxa, and that lMales lacking supraorbital spine; antennal spine undivided. Mature females with relatively short P5, P5 meri the overreaching the level of gastric pits in folded position in H. monstrosa.z

Apart from the key quoted above, the new species, H. hakuhoae, which is represented only by the female holotype, is seemingly close to H. kai in having the narrow carapace without a constriction between the hepatic and branchial margins, although as mentioned above, the carapace and appendages are covered with short stiff setae different from long soft hairs in H. kai.

Distribution. The holotype, a female, was obtained at 2,030 m deep in the Sulu Sea, as the deepest record among species of Homolodromia.