Uroptychus pollostadelphus, Baba, 2018

Baba, Keiji, 2018, Chirostylidae of the Western and Central Pacific: Uroptychus and a new genus (Crustacea: Decapoda: Anomura), Tropical Deep-Sea Benthos (Mémoires du Muséum national d'Histoire naturelle 212), pp. 1-612 : 411-414

Uroptychus pollostadelphus n. sp.

Figures 203 , 204

TYPE MATERIAL — Holotype: New Caledonia, Norfolk Ridge. NORFOLK 2 Stn DW 2103, 23°56.96’S, 167°43.70’E, 717- 737 m, 30.X.2003, ♂ 6.8 mm ( MNHN-IU-2014-16864 ).

ETYMOLOGY„ From the Greek pollostos (smallest) plus adelphos (twin), alluding to a pair of very small epigastric spines.

DISTRIBUTION„ Norfolk Ridge; 717- 737 m.

DESCRIPTION„ Carapace: Nearly as long as broad; greatest breadth 1.7 × distance between anterolateral spines. Dorsal surface smooth and glabrous, slightly convex from anterior to posterior; epigastric region with pair of very small spines. Lateral margins convexly divergent posteriorly; anterolateral spine small, reaching tip of lateral orbital spine; denticulate short ridge on anterior end of branchial region, followed by row of obsolescent denticles. Rostrum straight horizontal, narrow triangular, with interior angle of 20°; dorsal surface flattish; length about half that of remaining carapace, breadth slightly less than half carapace breadth at posterior carapace margin. Lateral limit of orbit angular, ending in very small spine, distinctly anterior to level of anterolateral spine. Pterygostomian flap nearly smooth on surface, anteriorly roundish, with angular end.

Sternum: Excavated sternum anteriorly sharp triangular, surface with small spine in center. Sternal plastron slightly shorter than broad, lateral extremities gently divergent posteriorly. Sternite 3 moderately depressed, with broad V-shaped anterior margin bearing 2 submedian spines separated by narrow notch. Sternite 4 having anterolateral margin slightly convex, anteriorly ending in blunt but distinct process, slightly more than 1.5 × as long as posterolateral margin. Sternite 5 having anterolateral margin moderately convex, as long as posterolateral margin of sternite 4.

Abdomen: Smooth and glabrous. Somite 1 well convex from anterior to posterior. Somite 2 tergite 2.6 × broader than long; pleuron posterolaterally bluntly angular, lateral margin concave and moderately divergent posteriorly. Pleuron of somite 3 tapering to angular tip. Telson 0.6 × as long as broad; posterior plate emarginate on posterior margin, length 1.7 × that of anterior plate.

Eye: 1.7 × longer than broad, overreaching midlength of rostrum, mesial margin concave, lateral margin convex. Cornea slightly inflated, length subequal to that of remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 2 × longer than high. Antennal peduncle slightly overreaching cornea. Article 2 with small but distinct distolateral spine. Antennal scale reaching distal end of article 5, 1.8 × broader than article 5. Distal 2 articles unarmed. Article 5 twice as long as article 4, breadth about one-third height of antennular ultimate article. Flagellum consisting of 16 segments, barely reaching distal end of P1 merus.

Mxp: Mxp1 with bases close to each other. Mxp3 sparsely setose on lateral surface. Basis with 1 denticle on mesial ridge. Ischium with 14 denticles on crista dentata, flexor margin not rounded at distal end. Merus 2.2 × longer than ischium, moderately ridged along flexor margin, and unarmed. Carpus also unarmed.

P1: 5.3 × longer than carapace, smooth and barely setose except for fingers. Ischium with short, subtriangular dorsal spine; ventromesial margin bearing a few tubercles, lacking subterminal spine. Merus 1.25 × longer than carapace, with low blunt distomesial and distolateral processes ventrally. Carpus unarmed, length 1.3 × that of merus. Palm 3.0 × longer than broad, slightly shorter than carpus. Fingers relatively broad distally, ending in small, somewhat incurved spine, slightly crossing when closed; movable finger half as long as palm, opposable margin with basally broad (disto-proximally), distally bilobed process; fixed finger with median prominence on opposable margin.

P2-4: Slender. Meri mesio-laterally compressed, unarmed; P2 merus slightly shorter than carapace, subequal to P3 merus in length and breadth, 1.2 × longer than P2 propodus; P3 merus subequal to length of P3 propodus; P4 merus much smaller than P3 merus (0.6 × length and 0.7 × breadth of P3 merus), 0.8-0.9 × length of P4 propodus; length-breadth ratio, 4.9 on P2, 4.5-4.7 on P3, 3.6-3.8 on P4. Carpi subequal in length on P2 and P3, shorter on P4; carpus-propodus length ratio, 0.5 on P2 and P3, 0.4-0.5 on P4; carpus-dactylus length ratio, 1.5 on P2, 1.3 on P3, 1.0 on P4. Propodi longest on P3, shortest and narrowest on P4; flexor margin straight, with pair of terminal spines preceded by 9 spines along entire length on P2, 7 spines on P3, 4 spines on P4. Dactyli longest on P3, shortest on P4, shorter than carpi on P2 and P3, about as long on P4; dactylus-propodus length ratio, 0.40 on P2 and P3, 0.46-0.47 on P4; flexor margin strongly curving at proximal third, with 9 or 10 triangular, moderately inclined spines diminishing toward base of article, ultimate strongest, penultimate close to ultimate, antepenultimate more proximal to midlength between penultimate and distal quarter.

REMARKS — This species strongly resembles U. sagamiae Baba, 2005 in nearly all details, from which it is differentiated by sternite 4, which is smooth instead of granulose on the posterior surface; the P1 palm is ventrally smooth instead of granulose; and the extensor margins of P2-4 dactyli have no plumose setae as in U. sagamiae . Both species are mediumsized, so the above mentioned differences may not be considered as age related variations.

The new species also resembles U. benthaus n. sp. (see above) in the carapace ornamentation especially bearing a relatively small anterolateral spine and a pair of small epigastric spines, and in the spination of P2-4 propodi and dactyli. Uroptychus pollostadelphus is differentiated from that species by the P2-4 that are broader, e.g. the meri having the lengthbreadth ratio, 4.5-4.9 on P2-3, 3.6-3.8 on P4 instead of 6.1-7.0 on P2-3, 4.8-5.1 on P4; the P4 merus is much shorter, 0.6 instead of 0.7 times the length of P3 merus; and the pterygostomian flap bears the anterior margin almost roundish instead of sharply produced to a distinct spine.

The species also resembles U. septimus n. sp. Their relationships are discussed under the account of that species (see below).

Figures

FIGURE 203 Uroptychus pollostadelphus n. sp., holotype, male 6.8 mm (MNHN-IU-2014-16864). A, carapace and anterior part of abdomen, proximal part of right P1 included,dorsal. B, same,lateral.C, sternal plastron,with excavated sternum and basal parts of Mxp1. D, telson.E, left antenna,ventral.F, right Mxp3,ventral.G, same,lateral.H, right P1, dorsal.Scale bars:1 mm.

FIGURE 204 Uroptychus pollostadelphus n.sp.,holotype,male 6.8 mm (MNHN-IU-2014-16864).A, right P2,lateral.B, same,distal part,setae omitted,lateral.C, right P3, setae omitted, lateral. D, right P4,lateral.Scale bars:1 mm.