Pseudolambrus palauensis, Shaga & Priya & Ramar & Srinidhi & Mohan & Ranganathan & Moulvi & Mani, 2023

Shaga, I Bevin, Priya, K, Ramar, Selvakumar, Srinidhi, S, Mohan, G Chandra, Ranganathan, Sukanya, Moulvi, S M M & Mani, Bhuvaneswari, 2023, A Small Collection of Subtidal Crabs (Crustacea: Decapoda: Brachyura) from the Palau Islands Collected by Dredging, Bulletin of the National Museum of Nature and Science. Series A, Zoology 49 (1), pp. 7-42 : 14-18

Pseudolambrus palauensis sp. nov.

( Figs. 4–6)

urn:lsid:zoobank.org:act:D0E0AC18-2CC4-465B-BA9E-9C6D0A69F5F8

Material examined. Kayangel Atoll , north of Babelthuap I., Palau Is., lagoon, dredged, 4 m in depth; 1 Ə (cb 9.7×cl 9.5 mm), holotype, NSMT-Cr 30966; July 6, 1980; K. Baba leg.

Description of holotype. Carapace equilateral triangle in general outline; dorsal surface not strongly convex ( Figs. 4B, 5A, 6A); frontal region ( Figs. 4B, 5A, C) deflexed, its dorsal surface con- cave between weakly convex supraorbital surface of both sides, rather longitudinally grooved, reaching posteriorly to transverse depression connecting posterior parts of both orbits; gastric region weakly convex, armed with pair of obtuse tubercles side by side at anterior part, obtuse tubercle of similar size at posterior median part, some smaller granules dispersed on entire surface. Submedian surface behind each gastric region distinctly depressed in front of cardiac region ( Figs. 4B, 5A, 6A). Anterior part of cardiac region raised, with small obtuse granules symmetrically arranged; posterior part more or less ridged transversely, with row of several obtuse granules. Intestinal region transverse in front of carapace posterior margin. Branchial region ( Figs. 4B, 5A, 6A, 5D) prominent, curved, rather raised along carapace lateral margin.

Front ( Fig. 6A–B) about one-third as wide as carapace between posterior ends of supraorbital margins of both sides, more or less lobular, slightly narrowing distally; distal half about equal to supraorbital eave in length; distal margin roundly truncated, with median one-third obtusely angulated as triangular tooth. Supraorbital eave ( Fig. 6A–B) with margin only weakly concave in dorsal view, weakly retreating posteriorly; dorsal surface convex dorsally; both of intercalated and external orbital teeth distinctly lobate, thin, each with rounded tip. Small tubercle just behind external orbital tooth. Carapace anterolateral margin short, longitudinal, unarmed. Branchial margin ( Figs. 4B, 5A–B, 6A) convex, slightly longer than carapace anterolateral margin, armed with several isolated, thin teeth; posterolateral margin with 2 or 3 tubercles. Third maxilliped ( Figs. 5B, 6C) roughened, uneven, with obtuse tubercles of variable sizes; outer margin of merus nearly straight, with obtuse antero-external angle.

Both chelipeds ( Fig. 4) comparatively slender, about 2.2 times longer than carapace width, slightly different in shape. Merus subequal to palm in length, marginally armed with small tubercles of different sizes. Carpus short, with small tubercles. Left palm rather slender, with same thickness throughout length, but right palm stout as a whole, slightly thickened distally; tuberculation similar to both palms; 2 thin tubercles and 1 much stronger tubercle at basal and distal parts of upper margin, respectively; outer surface roughened with small conical granules and longitudinal row of granules in midline. Fingers of left chela small, but those of right chela thick, leaving wide gap between both fingers. All ambulatory legs missing.

Pleon ( Fig. 5B) wholly roughened with granules; third to fifth pleonites fused; fifth and sixth pleonites with subparallel lateral margins; telson nearly triangular in general outline, with sharp tip. G1 ( Fig. 6D) stout, tapering distally, with terminal part flattened, weakly curved, semitrans- parent, hairy.

Remarks. The wide and weakly deflexed front with a dorsal longitudinal depression is somewhat similar to those of the Rhinolambrus species such as R. lamelliger (White, 1847) [ White, 1847a –b, as Lambrus lamelliger sp. nov.; Adams and White, 1848, as Lambrus lamellifrons ; Rathbun, 1906, as Parthenope (Rhinolambrus) lamelligera ; Dai et al., 1986, Dai and Yang, 1991, as P. (R.) lamellifrons ; Takeda and Marumura, 2019, as R. lamelliger ], and R. pelagicus ( Rüppell, 1830) [ Rüppell, 1830, as Lambrus pelagicus sp. nov.; A. Milne-Edwards, 1872, as L. affinis sp. nov.; Rathbun, 1907, as Parthenope (Parthenope) melana sp. nov.; Flipse, 1930, as L. (R.) latifrons sp. nov.]. However, in the species of the genus Rhinolambrus A. Milne-Edwards, 1878 , the gastric, cardiac, intestinal and branchial regions are strongly bulged and armed with some strong and sharp tubercles, and the hepatic region has a distinctly produced conical tooth on the carapace anterolateral margin between the external orbital angle and the branchial margin; these characters are not possessed by the present specimen.

As frequently remarked in some precedent papers, the genus Pseudolambrus , to which the present new species is referred, is heterogenous, with the various external appearance of the known species. The present new species is without doubt most close to P. sundaicus Ng and Rahayu, 2000 , which was originally described from Jakarta Bay, Java, Indonesia, and additionally recorded from Okinawa-jima Island in the Ryukyu Islands by Maenosono (2016). In both papers, the fine photographs of the specimens were given for the adequate comparison with the present new species.

Pseudolambrus palauensis sp. nov. has the sloping shoulders of the carapace branchial margins, with the laterally angulated branchial margin ( Figs. 4B, 5A–B, 6A), whereas in P. sundaicus , the brachial margin is regularly convex and nearly longitudinal behind the shoulder. In the new species, the external orbital and intercalated teeth are distinctly flattened and directed outward, and thus the orbit seems to be somewhat opened and imperfect, but in P. sundaicus , both the teeth are directed forward and tightly close to make complete orbit. There is a small tubercle just behind the external orbital tooth in the new species, but in P. sundaicus , such a small tooth is absent at the place with the long-necked appearance. In the new species, the antero-external angle of the third maxilliped merus is produced and weakly angulated, instead in P sundaicus , it is distinctly rounded. The G1 of the new species is weakly flattened at the distal part, but that of P. sundaicus is subtruncated at the tip.

Etymology. The new species named after the type locality, the Palau Islands.

Distribution. Known only by the holotype male from the Kayangel Atoll, north of Babelthuap Island in the Palau Islands, 4 m in depth.