Uroptychus ngae, Dong & Zhou & Li, 2024

Dong, Dong, Zhou, Yadong & Li, Xinzheng, 2024, A new species of Uroptychus Henderson, 1888 (Decapoda: Anomura: Chirostylidae) from a seamount in the South China Sea, Zootaxa 5476 (1), pp. 82-88 : 83-87

Uroptychus ngae sp. nov.

( Figs. 1–3 )

Type material. Holotype: SY358-B1-A2, ovig. female (pcl 5.7 mm), Zhongnan seamount, South China Sea, 116.72°E, 16.63°N, 761 m, voyage TS2-5, coll. Shenhai Yongshi manned submersible on R / V Tansuo 2, 24 March 2021 . Paratype: SY358-B1-A1, 1 male (pcl 4.9 mm), same data as holotype .

Description. Carapace: Approximately 1.3 × broader than long (excluding rostrum). Outer orbital angle with acute spine. Lateral margins convex, broadest at posterior branchial margin; anterolateral spine strong, lateral to outer orbital angle and distinctly overreaching tip of outer orbital spine; hepatic margins with 1 small spine; branchial margin armed with row of spines decreasing in size posteriorly, anterior-most spine much stronger than remaining spines and usually with affiliated small spine dorsally or posteriorly. Posterior margin concave. Dorsal surface with sparse fine setae laterally; gastric region with row of epigastric spines; cervical groove indistinct. Rostrum triangular and relatively broad, approximately 1.2 × longer than broad, one-third of remaining carapace length and 0.2 × carapace breadth; dorsal surface and lateral margins sparsely setose; lateral margins unarmed or each with tiny spines on distal fourth. Pterygostomial flap with scattered small spines on anterior half of lateral surface; anterodorsal margin with 1 or 2 small spines; anterior end triangular, unarmed.

Thoracic sternum: Broader than long, widening posteriorly. Excavated sternum with triangular anterior margin, and longitudinal ridge along midline. Sternite 3 depressed well; anterior margin concave, with broad, Vshaped median excavation; anterolateral angle subtriangular; lateral margin straight. Sternite 4 with anterolateral angle spinose, reaching at most midlength of lateral margin of sternite 3; anterolateral margin denticulate, 2.2 × posterolateral margin length. Sternites 5 with anterolateral margin convex.

Abdomen: Tergites glabrous and unarmed.

Telson: Approximately 2.3 × broader than long; distal portion as long as proximal portion, distal margin with shallow, broad median notch.

Eye: Reaching distal 0.4 of rostrum; peduncle slightly convergent distally; cornea somewhat dilated, approximately one-third of remaining peduncle length.

Antenna: Peduncle reaching distal one-fifth of rostrum (excluding distal spine).Article 2 with strong distolateral spine anterolaterally directed. Articles 4 and 5 each armed with strong distoventral spine on mesial side. Article 5 approximately 1.3 × article 4 length. Antennal scale triangular, 4.1 × longer than broad, slightly broader than antennal peduncle at base, overreaching distal end of article 5 excluding terminal spine.

Maxilliped 3: Ischium approximately as long as merus; crista dentata with tiny denticles increasing in size proximally. Merus divergent distally; flexor margin straight, with produced distomesial lobe bearing 3 or 4 spines; distal margin with distinct spine; extensor margin unarmed. Carpus short, with spine on distal margin. Propodus elongate, with low lobe on proximal third part.

P1: subequal, approximately 3.6 × pcl; surfaces of each segment having numerous short rugae in longitudinal rows bearing fine setae. Ischium with stout dorsodistal spine; ventral margin distally produced, with distinct mesial subterminal spine followed with 2 or 3 small spines. Merus subcylindrical, 0.8 × pcl, 2.7 × longer than broad; distal margin bearing strong dorsomesial and ventromesial spines and relatively small dorsolateral and ventrolateral spines; dorsodistal margin unarmed or with small tubercles; mesial face with strong median spine followed with row of small spines proximally and another row of small spines on ventral side. Carpus subcylindrical, equal or slightly longer than meri, 0.9 × pcl, 2.6 × longer than broad; distal margin with small dorsomesial spine, ventromesial spine and 2 ventrolateral spines; dorsodistal margin with minute tubercles; dorsal surface with 1 or 2 small spines proximally. Palm relatively compressed, 1.2 × pcl, 3.0 × longer than broad. Fingers distally bearing dense long setae; approximately half of palm length; tips acute, slightly crossing over each other; occlusal margins minutely denticulate, medially convex on fixed finger, with distinct submedian tooth on dactylus, and low subterminal tooth on both fingers.

P2–4: Dense fine setae on each article. Meri laterally compressed, subequal in breadth and decreasing in length from P2–4; P2 merus 0.7 × pcl and 3.4 × longer than broad, P3 merus weakly shorter than P2 merus length, P4 merus 0.7 × P2 merus length; extensor margin with minute spines on proximal part (spines obsolescent on P4), and small distal spine on P2; flexor margin with distinct distal spine on P2 and P3. Carpus decreasing in length from P2–4; P2 carpus approximately half of P2 merus length, P3 and P4 carpus approximately 0.9 × P2 carpus length; extensor margin slightly rugose. Propodus stout, P3 propodus longer than P4 and P2 propodus, P2 and P3 propodus subequal in breadth and slightly broader than P4 propodus; P2 propodus 0.9 × P2 merus length (propodus/ merus length ratio: 1.0 on P3 and 1.2 on P4), and 3.5 × longer than broad (length/breadth ratio: 3.7 on P3 and 4.0 on P4); P2 propodus 0.9 × P3 and P4 propodus length; flexor margin gently convex at distal 0.3 to 0.4 part and distally narrowed to juncture with dactylus, with 5 or 6 corneous movable spines evenly interspaced on convex part and pair of distal corneous spines on distal narrow part close to propodus-dactylus junction, distal pair relatively remote from preceding spines. Dactylus about half propodus length, distinctly curved and gradually narrowing distally, terminating in strong claw-like spine; flexor margin with another 5 or 6 corneous spines decreasing in size proximally and evenly arranged on entire length.

Coloration. Carapace, abdominal somites and pereopods generally orange; dorsal surface of carapace with three longitudinal dark orange stripes extending onto abdominal somites.

Habitat. Seamount environment, associated with gorgonian coral Iridogorgia sp.

Distribution. South China Sea, West Pacific; at depth of 761 m.

Etymology. The species is named in honour of the late Dr. Ngan Kee Ng, Singapore, a good friend for years and a leading brachyuran taxonomist. Her friendship and kindness will be missed.

Remarks. Uroptychus ngae sp. nov. is morphologically similar to U. insignis ( Henderson, 1885) , U. macquariae Schnabel, Burghardt & Ahyong, 2017 , U. spinulosus Dong & Li, 2015 and U. zeidleri Ahyong & Poore, 2004 in having the spinous branchial margins, a row of epigastric spines, anterolateral spines overreaching outer orbital spines, and the similar spination pattern of the P2–4 dactylus. The new species can be differentiated from the four relatives in having the P2–4 propodi broadest at the distal 0.3–0.4, leaving the distal pair of spines relatively remote from the preceding ones; and the P1 carpus and merus less spinose, lacking distinct spines on the dorsal surfaces and dorsodistal margins. In the latter four species, the P2–4 propodus is broadened distally with all the flexor spines closely interspaced on the convex part; and the P1 merus and carpus are armed with spines or sharp tubercles on the dorsal surfaces and dorsodistal margins. The new species further differs from U. insignis , U. macquariae and U. spinulosus in having a strong anterior branchial marginal spine (on the anterior end of the anterior branchial margin) as large as or somewhat larger than the anterolateral spine and continuous with the following lateral spines; and the pterygostomial flap armed with small spine(s) on the anterodorsal margin (between the anterior terminal and the linea anomurica). Whereas in the three related species, the anterior branchial marginal spine is much smaller than the anterolateral spine and is separated from the following spines by an unarmed interval; and the anterodorsal margin of the pterygostomial flap is unarmed. The new species further differs from U. zeidleri in having 1 instead of 2 rows of spines ventrally on P1 ischium. It also further differs from U. spinulosus in having the hepatic margin armed with 1 or 2 spines (unarmed in the latter), and the flexor marginal spines of the P2–4 propodus restricted on the distal half (with 1 proximal spine separated from the distal group in the latter).

The morphological characters of the P2–4 propodi and dactyli link the new species also to U. megistos Baba, 2018 , which is known from the Vanuatu and Solomon Islands. The new species, however, can be readily distinguished from U. megistos in the following characters: the dorsal surface of the carapace is glabrous (except for lateral parts) but bearing epigastric spines, instead of setose and unarmed; the maxilliped 3 carpus has a distal spine, instead of being unarmed; and the mesial face of the P1 merus bears a strong median spine instead of only denticle-like processes.

Partial COI sequence of the holotype was obtained (GenBank accession number PP735711). COI sequences of U. zeidleri , U. spinulosus and U. megistos are not available for comparison. The genetic distances of COI sequences between the U. ngae and U. insignis and U. macquariae is 13.2% and 12.7–12.9%, respectively, clearly indicating that the new species is distinct from the latter two species ( Schnabel et al. 2017; Schnabel 2020).

Figures

FIGURE 1. Uroptychus ngae sp. nov.: (A, C–H) SY358-B1-A2, holotype, ovigerous female; (B) SY358-B1-A1, male paratype. A, carapace and abdominal somites 1–3, setae on carapace illustrated on left side, dorsal view; B, carapace, dorsal view; C, carapace, left pterygostomian, lateral view; D, sternal plastron, ventral view; E, telson, extensor view; F, left antennal peduncle, ventral view; G, left third maxilliped, lateral view; H, crista dentata on left maxilliped 3 ischium, ventral view. Scale bars equal 1.0 mm.

FIGURE 2. Uroptychus ngae sp. nov., SY358-B1-A2, ovigerous female holotype: A, left P1, setae illustrated on lateral part of merus, dorsal view; B, left P1 ischium, merus and carpus, ventral view; C, right P2, setae illustrated, lateral view; D, right P3, lateral view; E, right P4, lateral view; F, left P2 dactylus and distal part of propodus, lateral view. Scale bars equal 1.0 mm.

FIGURE 3. Uroptychus ngae sp. nov., SY358-B1-A1, male paratype, colour in life, dorsal view.