Uroptychus transparens, Dong & Gan & Li, 2021

Dong, Dong, Gan, Zhibin & Li, Xinzheng, 2021, Descriptions of eleven new species of squat lobsters (Crustacea: Anomura) from seamounts around the Yap and Mariana Trenches with notes on DNA barcodes and phylogeny, Zoological Journal of the Linnean Society 192 : -

UROPTYCHUS TRANSPARENS SP. NOV.

( FIGS 11, 12; SUPPORTING INFORMATION, FIG. S2D, E)

Zoobank registration: urn:lsid:zoobank.org:act:15DD3B83-EA3F-443B-BCD2-01FF579E48B4

Material examined: Holotype, MBM189199 , one male ( PCL 9.1 mm), stn. FX-DIVE 65, M2 seamount near the Mariana Trench , West Pacific, 11°18.34’N, 139°21.43’E, 299 m, coll. Faxian ROV on R / V Kexue, 16 March 2016.

Description: Carapace (excluding rostrum) 1.2 times longer than broad. Outer orbital angle triangular, with small spine. Lateral margins divergent posteriorly; anterolateral spine strong, over-reaching outer orbital angle; hepatic margins with acute tiny spines; anterior branchial margin armed with strong spine at lateral base of anterior cervical groove followed by small spine and accompanied with tiny dorsal spines; posterior branchial margin with four spines diminishing in size posteriorly. Posterior margin concave. Dorsal surface glabrous, with pair of epigastric ridges bearing small spines; another small, median spine present between epigastric ridges. Rostrum broadly triangular, approximately 0.4 times of remaining carapace length, 1.1 times as long as broad; dorsal surface slightly depressed; lateral margins straight, weakly serrated. Pterygostomial flap medially concave, anterior end with acute spine.

Sternal plastron as long as broad. Sternite 3 with surface deeply depressed; anterior margin deeply concave, with pair of strong submedian spines flanked by several distinct spines; anterolateral corners rounded. Sternite 4 with anterior part depressed, separated from posterior part by pair of transverse ridges, anterolateral corner armed with strong spine; anterolateral margin denticulate, more than three times the posterolateral margin length. Sternites 5–7 with transverse ridges interrupted by midline groove.

Abdominal tergites glabrous and unarmed.

Telson approximately 1.6 times broader than long; distal portion 1.9 times proximal portion length.

Eyestalk long, reaching distal 0.2 of rostrum; cornea slightly dilated, 0.3 times remaining peduncle length; lateral margins of peduncles straight.

Antennal peduncle reaching distal 0.2 of rostrum. Article 2 without distolateral tooth. Article 4 and 5 each with distinct distal ventromesial spine; article 5 approximately thrice longer than article 4. Antennal scale dagger-shaped, 4.1 times as long as broad, 1.4 times broader than article 4 and 5, distinctly overreaching distal end of article 5.

Third maxilliped slender, each article glabrous on ventral surfaces. Basis with three denticles on mesial ridge. Ischium subcylindrical; crista dentata with about 21 denticles. Merus slender and subcylindrical, 1.5 times as long as ischium; distoflexor margin entire; extensor margin with distinct distal spine. Carpus subcylindrical, with minute distal spine on extensor margin.

P1 long and subequal, approximately 5.6 times PCL; merus, carpus and palm subcylindrical. Ischium armed with strong dorsodistal spine; ventrodistal margin unarmed. Merus 1.3 times PCL, broaden distally; surfaces with scale-like rugae or flat tubercles. Carpus 1.3 times merus length; surfaces with elevated scalelike rugae bearing simple setae. Palm 1.2 times merus length, 2.9 times longer than broad, relatively broader than merus and carpus; surfaces with longitudinal rows of elevated rugae bearing simple setae, rugae near lateral and mesial margins usually pointed as acute tiny spines. Fingers setose on surfaces and margins, 0.4 times palm length; tips acute, slightly crossing over each other; occlusal margins minutely denticulate, with broad and low median tooth on fixed finger, and subrectangular tooth on dactylus.

P2–4 slender; meri, carpi and propodi bearing long, simple setae on surfaces, dactyli bearing relatively short setae. Ischia with small disto-extensor tubercle. Meri elongate, laterally compressed, decreasing in length from P2 to P4; P2 merus 1.1 times PCL and 5.8 times longer than broad, P3 merus 0.9 times P2 merus length, P4 merus 0.7 times P2 merus length; extensor margin with a row of small spines on proximal part, such spines degenerated and ruga-like on P3 and P4; flexor margin with distal spine (absent on P4). Carpi subequal in length on P2–4, 0.4 times P2 merus length; extensor margin of P2 with small distal spine. Propodi laterally compressed, P2 propodus slightly shorter than P3 and P4 propodi, P2 propodus half of P2 merus length and 5.7 times longer than broad, P3 and P4 propodi 1.2 times P2 propodus length; flexor margin straight, with a row of corneous spines (15, 14 and 12 spines on P2–4, respectively) evenly arranged, including distal pair. Dactyli approximately 0.3 times propodus length; flexor margin bent on proximal one-third, with 11 or 12 corneous spines evenly on entire length, distalmost spine largest and claw-like.

Coloration: Shell totally transparent; tubercles and rugae yellow. Internal organs within carapace darkorange, muscles and branchiae somewhat white.

Habitat: On rocky substrate around golden coral Chrysogorgia gracilis Xu et al., 2020 .

Distribution: West Pacific, seamount near the Mariana Trench; depth 255– 311 m.

Etymology: From Latin, trans, through, and parere, to appear, meaning ‘transparent’, referring to the unusual transparent shells of this species.

Remarks: The new species closely resembles U. longioculus Baba, 1990 , U. flindersi Ahyong & Poore, 2004 and U. poupini Baba, 2018 in having a broad rostrum, elongate eyestalks, spinose branchial margins, and the same spination form on the P2–4 dactyli. Uroptychus transparens differs from its three relatives in having numerous elevated rugae or tubercles on each P1 segment (especially on the palm), the anterior margin of sternite 3 armed with several distinct spines in addition to the submedian spines, and the antennal scale distinctly over-reaching the end of the peduncle; in contrast, the other three species have glabrous P1 surfaces (especially on the palm and dorsal surfaces of each segment), the anterior margin of sternite 3 armed only with submedian spines, and the antennal scale barely reaching the distal end of the peduncle. Uroptychus transparens further differs from U. longioculus and U. poupini in having relatively stouter P2–4 meri: the length–breadth ratio of the P2 merus in the new species is 5.8; in contrast, this ratio in U. longioculus is 8.0, according to the illustrations of the holotype (Baba, 1990), and is 7.3–9.7 in U. poupini (Baba, 2018) . Uroptychus transparens further differs from U. flindersi in having a pair of epigastric ridges, more pronounced spines on the branchial margins, and a single spine at the base of the cervical groove rather than a bifid spine.

No DNA information for the closely related species was available for comparative analysis. The DNA sequences of the new species are provided in this study.