Uroptychus marianicus, 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 MARIANICUS SP. NOV.

( FIGS 9, 10; SUPPORTING INFORMATION, FIG. S1E, F)

Zoobank registration: urn:lsid:zoobank.org:act:83531A55-9C0C-48C4-B8B5-A0DAFD9AF9DB

Material examined: Holotype, MBM189198 , one male ( PCL 11.2 mm), stn. FX-DIVE 61, M2 seamount near the Mariana Trench , West Pacific, 11°20.94’N, 139°20.37’E, 808 m, coll. Faxian ROV on R / V Kexue, 18 March 2016.

Description: Carapace (excluding rostrum) as long as broad. Outer orbital angle with small acute spine. Lateral margins convex; anterolateral spine strong, followed with small spine on (right) hepatic margin; anterior branchial margin armed with strong spine on lateral base of anterior cervical groove; posterior branchial margin with three strong spines decreasing in size posteriorly. Posterior margin concave. Dorsal surface unarmed, covered with numerous short, transverse rugae or low ridges; regions well delineated; gastric, cardiac and posterior branchial regions distinctly elevated. Rostrum triangular, approximately half of remaining carapace length, 1.5 times as long as broad; dorsal surface with short rugae; distal portion of lateral margins slightly serrated. Pterygostomial flap with median transverse groove; anterior end with small acute spine; surface with short rugae.

Sternal plastron as broad as long, widening posteriorly. Sternite 3 with surface deeply depressed; anterior margin concave, with pair of small submedian spines separated by broad V-shaped notch; anterior ends with acute spines; lateral margins with distinct spines. Sternite 4 with anterior part depressed, separated from posterior part by low transverse ridges, anterolateral corner greatly produced reaching level of anterior end of sternite 3, and each armed with two strong spines affiliated with small spines; anterolateral margin indistinctly serrated, as long as posterolateral margin. Sternites 5–7 with transverse ridges interrupted by midline groove.

Abdominal tergites 1–3 each with transverse ridge on dorsal surface.

Telson approximately 2.2 times broader than long; distal portion 1.5 times proximal portion length.

Eyestalk reaching distal 0.6 of rostrum; cornea not dilated, approximately half of remaining peduncle length.

Antennal peduncle reaching distal 0.3 of rostrum. Article 2 with distinct distolateral tooth. Article 4 and 5 each with distal ventromesial spine; article 5 twice as long as article 4. Antennal scale subtriangular, 2.9 times as long as broad, twice broader than article 4 and 5, barely reaching distal end of article 5.

Third maxilliped slender. Basis with about five denticles on mesial ridge. Ischium having crista dentata with about 16 denticles. Merus 1.4 times as long as ischium; flexor margin denticulate on distal half; extensor margin with small median spine and strong distal spine. Carpus subcylindrical; extensor margin bearing small spines.

P1 elongate, right P1 slightly longer than left P1 and approximately 5.0 times PCL; surfaces of each segments covered with rows of scale-like rugae bearing fine setae; merus, carpus and palm subcylindrical. Ischium armed with strong dorsodistal spine and affiliated small spines; ventromesial margin bearing row of spinules and two strong subterminal spines (proximal one longest). Merus 1.1 times PCL; distal margin with few small dorsal spines, strong mesial spine and two strong ventral spines each on mesial and lateral sides; dorsomesial margin with strong spine near distal margin followed by small spines or pointed tubercles; mesial margin with strong median spine and additional one to thee proximal spines; ventral surface armed with a row of small spines or pointed tubercles along midline. Carpus longer than merus, approximately 1.6 times PCL; distal margin with small dorsal spine, strong mesial spine and two strong ventral spines each on mesial and lateral sides; rugae on proximal part of surfaces somewhat elevated and pointed. Palm relatively compressed; right palm 3.5 times longer than broad, 1.1 times left palm length, 1.7 times PCL. Fingers densely setose on surfaces and margins, 0.4 times of right palm length; occlusal margins distally straight and minutely denticulate, distinctly concave on proximal part, with noticeable gap between two fingers.

P2–4 stout; rugae of surfaces bearing soft setae. Ischia with two strong disto-extensor spines. Meri relatively compressed, decreasing in length posteriorly; P2 merus 0.8 times PCL and 4.4 times longer than broad, P3 merus 0.9 times P2 merus length, P4 merus 0.8 times P2 merus length; extensor margin armed with a row of spines, distalmost spine accompanied with one or two small lateral spines; flexor margin with strong distal spine (two spines on right P3), and few minute spines along P2 mesioflexor margin. Carpi short, subequal in length, 0.4 times P2 merus length; extensor margin with two longitudinal rows of spines (spines of lateral row relatively degenerated on P3 and P4), distal spine of each row prominent. Propodi subcylindrical, slightly increasing in length from P2 to P4, P2 and P3 propodi approximately 0.9 times P2 merus length and 5.3 times longer than broad, P4 propodus 1.1 times P2 propodus length; flexor margin straight, with pair of movable, corneous distal spines preceded by two or three similar spines on distal half. Dactyli 0.5–0.6 times propodi length; flexor margin straight or weakly bent, evenly armed with 17–19 comb-like corneous spines (17, 18 and 19 on P2–4, respectively), distal two spines relatively larger, penultimate spine broadest.

Coloration: Carapace reddish purple on hepatic and gastric regions; other regions orange. Sternal plastron and abdominal tergites light yellow. Pereopods orange.

Habitat: Associated with a gorgonian coral species of Primnoidae .

Distribution: West Pacific, a seamount near the Mariana Trench; depth 808 m.

Etymology: The specific name refers to the Mariana Trench, which is located near where the holotype was sampled.

Remarks: Uroptychus marianicus closely resembles U. nanophyes McArdle, 1901 , U. longior Baba, 2005 and U. worrorra McCallum & Poore, 2013 in having at least four strong (principal) spines on the branchial lateral margin, prominent anterolateral spine(s) on sternite 4, a row of spines on the extensor margin of the P2–4 meri, and having the same spine arrangement of the P2–4 dactyli. Uroptychus marianicus is closer to U. nanophyes in having small spines on the P2 mesioflexor margin. The new species is readily differentiated from its three relatives in having four prominent spines on the branchial margin, the carapace devoid of minute dorsal spines or pointed tubercles, well-delineated carapace regions, and each of the anterolateral corners of sternite 4 with two strong spines; whereas the latter three species have at least five prominent spines on the branchial margin, scattered dorsal spines or spinelike tubercles on the carapace, indistinctly delineated carapace regions, and anterolateral corners of sternite 4 each with a single strong spine (MacArdle, 1901; Van Dam, 1940; Baba, 2005; McCallum & Poore, 2013). Uroptychus marianicus further differs from U. nanophyes in having several small spines only on the extensor margin of the third maxilliped carpus instead of a strong distal spine ( Baba, 2005, 2018). The new species further differs from U. longior and U. worrorra in having the antennal scale barely reaching instead of distinctly over-reaching the peduncle end, and the P1 covered in sparse short setae instead of dense and long setae. The new species also has more corneous spines (17–19) on the P2–4 dactyli flexor margin; in contrast, U. nanophyes and U. longior only have 12–13 spines, and U. worrorra has 14–16 spines.

No DNA information for the related species was available in GenBank for comparative analysis. The DNA sequence data for the new species are provided in this study.