Uroptychus deliquus Baba, Corbari & Macpherson, 2024

Anker, Arthur, Rodríguez-Flores, Paula C., Bähr, Susanne, Barreca, Federica, Dunn, Natalie, Rodrigue, Mattie, Qurban, Mohammed, Duarte, Carlos M. & Pieribone, Vincent, 2025, Previously undetected diversity of mesophotic squat-lobsters in the Red Sea, exemplified by a new species of Sadayoshia Baba, 1969 and a new record of Uroptychus deliquus Baba, Corbari & Macpherson, 2024 (Anomura: Galatheoidea and Chirostyloidea), Zootaxa 5686 (4), pp. 572-586 : 578-581

Uroptychus deliquus Baba, Corbari & Macpherson, 2024

( Figs. 4 , 5 , 6B )

Material examined. 1 male (CL 5.7 mm, PCL 4.0 mm), FLMNH UF 68646 , Saudi Arabia, Red Sea , about 60 km off Al Birk , Red Sea Decade Expedition Leg 2, Neptune Sub dive NTN0131, 17.820978, 40.709915, depth: 220 m, Neptune Dive Team, processed by F. Benzoni and F. Barreca, 30.03.2022 (NTN0131-Bio2B / OCX-091) [GenBank Acc. No: PV626998] .

Description. Red Sea specimen. Carapace. About as long as wide, greatest width measured at posterior third, 1.6 times distance between anterolateral spines. Dorsal surface setose, unarmed, moderately convex. Lateral margins medially convex, with 8 spines; 1 st anterolateral, directed straight forward, situated lateral to small orbital spine, separated from latter by its basal width, overreaching orbital spine; 2 nd and 3 rd spines small, inserted on hepatic margin, 3 rd spine smaller; 4 th –7 th spines on branchial margin, well developed; 8 th and last spine very small. Rostrum narrowly triangular, trifid, with small subterminal spine on each side, straight horizontal, 1.7 times as long as wide, 0.6 times as long as carapace length; with about half-distance between anterolateral spines, and half carapace width measured at posterior margin. Pterygostomian flap anteriorly produced into sharp spine; surface covered with small spines on anterior half, diminishing in size ventrally.

Thoracic sternum. Sternal plastron slightly longer than broad; lateral margins subparallel; sternite 5 slightly narrower than sternite 4; sternite 6 subequal in width to sternite 4; sternite 7 slightly broader than sternite 6. Surface of sternite 3 shallowly depressed in ventral view, anterolaterally rounded, with 2 small processes on lateral margin; anterior margin concavely excavated, with U-shaped median notch, without distinct flanking spines; lateral end with small spine. Sternite 4 with anterolateral margin anteriorly produced into spine, overreaching anterior end of sternite 3, about 1.2 times as long as posterolateral margin. Anterolateral margins of sternite 5 subparallel, anteriorly rounded, as long as posterolateral margin of sternite 4.

Pleon. Smooth. Pleonite 2 with tergite 3.3 times as wide as long; pleuron posterolaterally blunt. Pleuron of somite 3 posterolaterally blunt. Telson half as long as broad; posterior plate 1.4 times longer than anterior plate, posterior margin feebly convex or feebly concave.

Eye. Peduncle proximally broader, 1.7 times as long as broad, reaching half of rostrum distally. Cornea not dilated, half as long as remaining eyestalk.

Antennule and antenna. Ultimate article of antennular peduncle 3.5 times longer than high. Antennal peduncle overreaching eye and tip of rostrum.Article 2 with distinct distolateral spine. Antennal scale not overreaching article 5, 1.4 times as wide as article 5. Articles 4 and 5 each with strong distomesial spine. Article 5 1.3 times as long as article 4, its width 0.8 times that of ultimate article of antennule.

Mxp3. Ischium without distinct distoventral spine lateral to rounded flexor distal margin; crista dentata with about 12 denticles of variable size, some very small. Merus 1.2 times as long as ischium, mesial face flattish, flexor margin sharply ridged along distal third, with small distolateral tooth; extensor margin with subacute spine in distal half, with strong distal spine. Carpus with 3 spines on lateral and extensor surfaces, in addition to prominent distolateral spine.

P1. Moderately elongate, 3.4 times carapace length, densely covered with fine long setae, mostly in tufts. Ischium dorsally with 2 spines, distal spine strong, proximal spine very small; ventromesial margin with strong subterminal spine followed by several proximally diminishing, smaller spines. Merus about 1.3 times as long as carapace, with distinct spines as following: 4 ventral, 1 distomesial, 1 ventro-distomesial, 1 ventro-distolateral, and 3 obliquely arranged proximal ventromesial spines. Carpus subcylindrical, 1.5 times as long as merus, ventrally with 2 distal spines (mesial and lateral). Palm 3.4 times as long as broad, 1.2 times as long as carpus; mesial and lateral margins bluntly ridged. Fingers not gaping, distally slightly incurved; movable finger almost 0.5 (left) or 0.4 (right) times length of palm, opposable margin with subtriangular blunt proximal process, latter fitting into hiatus proximal to low eminence on opposable margin on fixed finger; remaining opposable margin of fixed finger sinuous.

P2–4. Meri compressed mesio-laterally, moderately broad; mesial face somewhat flattened, successively shorter posteriorly (P3 merus 0.9 times length of P2 merus, P4 merus 0.8 times length of P3 merus), subequally broad in P2–4; length-width ratio: 3.9 in P2, 3.8 in P3, 3.1 in P4; dorsal margin with few small proximal spines, latter always distinct on P2, occasionally obsolescent on P3, obsolete on P4; ventrolateral margin with 2 spines in distal half, distally produced into strong spine in P2, unarmed and distally lobe-like, not sharply produced in P3–4; P2 merus about 0.8 times length of carapace, slightly longer (about 1.1 times) than P2 propodus; P3 merus as long as P3 propodus; P4 merus 0.8 times length of P4 propodus. Carpi relatively short, subequal (slightly longer in P2 than in P3–4, or successively slighter shorter posteriorly), length less than half that of propodus; distal margin armed with spines in P2, unarmed in P3–4. Propodi subequal in P3–4, slightly shorter and stouter in P2; flexor margin slightly concave, with 1 pair of terminal movable spines preceded by 3–5 single movable spines on flexor margin. Dactyli subequal in length in P2–4, slightly shorter in P2 compared to P3–4, slightly longer than carpi (dactylus-carpus length ratio: 1.1 in P2, 1.2 in P3, 1.3 in P4); flexor margin nearly straight, bearing slender terminal spine preceded by 3 subtriangular spines, diminishing in size proximally and almost perpendicular to margin, and 3 more slender, somewhat inclined proximal spines; diminishing in size proximally.

Colour in life. Body and appendages ivory white, somewhat translucent ( Fig. 6B ).

Distribution and bathymetry. Western Indian Ocean: from southern Madagascar to the Red Sea, currently known depth range: 220–333 m ( Baba et al. 2024; present study).

Ecology. The holotype was found clinging to a gorgonian octocoral, Melithaea sp. ( Alcyonacea , Melithaeidae , species under study), strongly suggesting a symbiotic association ( Fig. 6A, C ).

Remarks. Within the speciose genus Uroptychus , U. deliquus most closely resembles U. galene Baba, Corbari & Macpherson, 2024 , which was described from Madagascar ( Baba et al. 2024), and also has affinities with U. tridentatus ( Henderson, 1885) from the Philippines and Indonesia, U. oxymerus Ahyong & Baba, 2004 from north-western Australia, and U. annae Baba, 2018 from New Caledonia and Vanuatu ( Baba 2005, 2018). All these species share (1) the general shape of the carapace; (2) the rostrum with subterminal spines; and (3) the presence of a median notch on the anterior margin of the third sternite in the sternal plastron.

The Red Sea specimen herein assigned to U. deliquus (hereafter U. deliquus — RS) is morphologically somewhat different from the type specimens of U. deliquus from Madagascar (hereafter U. deliquus — M). The two most noticeable differences between the Red Sea and Madagascan populations are (1) the third sternite is anterolaterally rounded, with 2 small processes on the lateral margin in U. deliquus —RS vs. anterolaterally sharply produced and bifid distally in U. deliquus — M; and (2) the flexor margin of the P2–4 propodi is armed with 3–5 spines in the distal half in U. deliquus —RS vs. armed with 1–3 spines in in U. deliquus —M (cf. Figs. 4 , 5 ; Baba et al. 2024). The genetic divergence in COI sequences between U. deliquus —RS and U. deliquus —M ranged between 2.5% and 3%. Our phylogenetic analysis recovered all populations of U. deliquus within a single clade ( Fig. 3 ), providing no support for the Red Sea population as a genetically distinct lineage that could be considered as a separate species. Nevertheless, the subtle morphological discrepancies, biogeographical criteria (Red Sea endemism among deep-water taxa, see Türkay 1996; Anker et al. 2023), and a relatively long branch of U. deliquus —RS may reflect an incipient speciation process.

Uroptychus deliquus (both—RS and—M) differs from U. galene by the anterolateral margin of the sternite 4 anteriorly produced into a well-developed spine, overreaching the anterior margin of sternite 3 vs. this spine being absent or minute in U. galene ; and the flexor margin of the P2–4 dactyli armed with 8–9 spines vs. 9–10 spines in U. galene . Finally, U. deliquus differs from U. tridentatus , U. oxymerus and U. annae by the anterolateral margin of sternite 4 anteriorly produced into a well-developed spine, overreaching the anterior margin of sternite 3, vs. not acutely produced or with a minute spine in the other species; the flexor margin of the P2–4 propodi armed with 3–5 spines in the distal half vs. 1–3 spines in the other species; the flexor margin of the P2–4 dactyli armed with 8–9 spines vs. 5–6 spines in U. tridentatus , 6–7 spines in U. oxymerus and 6 spines in U. annae ; the extensor margin of the Mxp3 merus armed with a subacute spine in its distal half vs. unarmed in the other species; and the flexor margin of the Mxp3 merus devoid of spines (except for distal spine) vs. armed with 1–2 spines distally to the meral mid-length in the other species (cf. Figs. 4 , 5 ; Ahyong & Baba 2004; Baba 2018; Baba et al. 2024).

Figures

FIGURE 3. Phylogenetic hypothesis resulting from IQTREE analyses of the COI gene (barcoding segment). GenBank Acc. No. is indicated for each taxon, except for new data generated for this study (indicated by FLMNH UF and MNHN).

FIGURE 4. Uroptychus deliquus Baba, Corbari & Macpherson, 2024: male (CL 5.7 mm), FLMNH UF 68646, off Saudi Arabia (Red Sea): A, carapace and anterior part of pleon, dorsal view; B, carapace, left side, lateral view; C, same, right side lateral view; D, anterior part of carapace, dorsal view; E, sternal plastron, with excavated sternum; F, right antenna, ventral view; G, right Mxp3, ventrolateral view; H, I, J, same, ischium, merus and carpus, dorsomesial (H), lateral (I) and mesial (J) (views (setae omitted); K, same, carpus, propodus and dactylus, lateral view; L, right P1, lateral view; M, same, carpus and chela, dorsal view; N, same, basis (distal portion), ischium, merus and carpus, mesial view; O, pleon, lateral view; P, telson, dorsal view (ventral when tucked); Q, pleonites 5 and 6, dorsal view.

FIGURE 5. Uroptychus deliquus Baba, Corbari & Macpherson, 2024: male (CL 5.7 mm), FLMNH UF 68646, off Saudi Arabia (Red Sea): A, right P2, lateral view; B, same, dactylus, mesial view; C, right P3, lateral view; D, right P4, lateral view.

FIGURE 6. Fan coral, Melithaea sp. (Melithaeidae, Alcyonacea), host of Uroptychus deliquus Baba, Corbari & Macpherson, 2024, off Saudi Arabia (Red Sea): A, colony of Melithaea sp. shortly after collection; B, male of U. deliquus (CL 5.7 mm), FLMNH UF 68646, clinging to the coral host; C, host colony of Melithaea sp. in situ, at a depth of 220 m. Photographs: F. Benzoni and F. Barreca (A, B); Neptune Dive Team (C).