Uroptychus pauroptilus, Baba & Macpherson & Rodríguez-Flores, 2025

Uroptychus pauroptilus sp. nov.

( Figs. 2–4 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

Type material. Holotype: Guinea Bissau. GB 1219, Stn L 53, 10°01'55"N, 17°25'01"W, 909 m, 30 November 2019: ovigerous female 5.8 mm (ICM-CBMR-D002846), sequenced, GenBank Acc. No. PQ 654352. GoogleMaps

Description. Carapace: Broader than long (length 0.8 × breadth); greatest breadth 1.9 × distance between anterolateral spines. Dorsal surface nearly smooth, moderately convex from side to side and anterior to posterior. Lateral margin convexly divergent posteriorly, with fine granulations supporting fine setae, not ridged along posterior portion. Anterolateral spine well developed, directed straight forward, situated very slightly posterior to small lateral orbital spine, and separated from that spine by its basal breadth, slightly overreaching base of antennal scale. Rostrum sharp, triangular, with interior angle of 22°, nearly horizontal, directed anteriorly; dorsal surface flattish, length 1.5 × breadth, 0.6 × length of remaining carapace, breadth 0.4 that of carapace measured at posterior margin. Pterygostomian flap smooth on surface, anteriorly somewhat roundish with tiny spine.

Thoracic sternum: Excavated sternum anteriorly convex, surface weakly convex from side to side. Sternal plastron broader than long (length three-quarters breadth); lateral extremities somewhat divergent posteriorly between sternites 4 and 6, subparallel between sternites 6 and 7. Sternite 3 weakly depressed in ventral view, anterior margin moderately excavated with median notch lacking flanking spine, anterolaterally minutely dentate; small spine at lateral terminus. Sternite 4 anterolateral margin convexly divergent posteriorly, anteriorly irregular, not produced into spine; length 1.5 × that of posterolateral margin. Anterolateral margin of sternite 5 convex, slightly longer than posterolateral margin of sternite 4.

Pleon: Smooth and glabrous. Pleomere 1 moderately convex from anterior to posterior. Pleomere 2 tergite 2.8 × broader than long, pleuron with lateral margin concavely divergent posteriorly, blunt at posterolateral terminus. Pleura of pleomeres 3–5 posterolaterally blunt. Telson 0.4 × as long as broad, slightly constricted between anterior and posterior plates; posterior plate as long as anterior plate, moderately concave on posterior margin.

Eye: Globular, as long as broad, barely reaching proximal one-third of rostrum. Cornea not dilated, subequally long as remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 3.9 × longer than high. Antennal peduncle overreaching eye, reaching midlength of rostrum. Article 2 with small but distinct distolateral spine. Antennal scale overreaching article 5 by basal segment of flagellum, breadth 2.4 × that of article 5, 0.5 × height of ultimate antennular article. Article 4 unarmed. Article 5 with very small distomesial spine; length 1.6 × that of article 4. Flagellum of 15 segments not reaching distal end of P1 merus, overreaching rostrum by more than one-third of its length, shorter than (0.8 ×) rostrum, 1.9 × length of articles 4 and 5 combined.

Mxp: Mxp1 with bases widely separated from each other. Mxp3 basis lacking distinct denticles on mesial ridge. Ischium crista dentata with about 30 very small denticles, flexor margin not rounded distally. Merus 2.4 × longer than ischium, mesial face distally flattish, flexor margin with 3 small spines distal to midlength, distolateral spine obsolete. No spine on carpus.

P1: 4.5 × longer than carapace, setose, ventral surface finely granulose on merus and carpus, smooth on palm. Ischium with small dorsal spine, ventromesially with obsolescent subterminal spine. Merus 1.1 × longer than carapace, with 2 distomesial (mesiodorsal and mesioventral) and 1 small distolateral ventral spine; dorsal surface spineless, distal margin minutely denticulate. Carpus subcylindrical, 1.2 × longer than merus, dorsally with minutely denticulate distal margin, ventrally with well-developed distomesial and small distolateral spine. Palm 1.1 × length of carpus, 4.5 × longer than broad, slightly depressed (height 0.8 × breadth). Fingers not gaping, 0.4 × length of palm, each ending in strongly incurved distal spine; opposable margin of movable finger with rounded proximal process, that of fixed finger sinuous.

P2–4: Setose as on P1; unarmed on meri and carpi. Meri successively shorter posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus 0.8 × length of P3 merus). P2 merus shorter than carapace (0.9 ×), 1.1–1.2 × longer than P2 propodus, P3 merus as long as P3 propodus, P4 merus 0.8 × length of P4 propodus; length-breadth ratio, 4.8 on P2, 4.3 on P3, 3.5 on P4. Carpi successively shorter posteriorly, shorter than propodi (carpus-propodus length ratio, 0.6 on P2, 0.5 on P3 and P4), longer than dactyli (carpus-dactylus length ratio, 1.4 on P2, 1.3 on P3, 1.1 on P4). Propodi subequally long on P2 and P4, slightly longer on P3; flexor margin moderately convex distally, with pair of terminal spines preceded by 7 or 8 basally articulated, long spines on P2, 7 spines on P3 and P4. Dactyli subequally long on P3 and P4, slightly shorter on P2, somewhat curving, length 0.4 × that of propodus, flexor margin with 9, somewhat obliquely directed, triangularly elongate, stout spines, distal 6 or 7 spines subequal, proximal spines successively smaller.

Eggs: Number of eggs carried, 20; size 1.10 × 1.39 mm to 1.16 × 1.32 mm.

Genetic data. Interspecific sequence divergence (COI):>15% ( U. nitidus , sequenced in this study); COI:>15% ( U. rubrovittatus , sequenced in this study). See phylogenetic tree ( Fig. 1 View FIGURE 1 ).

Etymology. From the Greek pauros (little) plus optilus (eye), referring to the small eye of the species.

Remarks. Among the six species of Uroptychus so far known from the eastern Atlantic ( Baba & Macpherson 2017), the following two species resemble U. pauroptilus sp. nov. in the carapace shape including the relatively long, sharply triangular rostrum, lack of submedian spines on the thoracic sternite 3 and the spination of the P2–4 dactyli: U. maroccanus Türkay, 1976 from off the coast of Morocco and U. tuerkayi Baba & Macpherson, 2017 from the Atlantis-Great Meteor Seamount Chain south of the Azores Islands.

The original description of U. maroccanus is rather brief, but additional morphological details were obtained by Baba & Macpherson (2017). Uroptychus pauroptilus sp. nov. is clearly distinguishable from U. maroccanus in the following differences: the lateral orbital spine is much smaller than, instead of well developed and larger than the anterolateral spine of the carapace; the carapace dorsum is almost smooth, instead of bearing small spines at least along the lateral margin; the pterygostomian flap is anteriorly somewhat roundish with a tiny spine, instead of being angular with a strongly produced spine; the excavated sternum is anteriorly rounded, followed by a weak median ridge, instead of being anteriorly sharp triangular, followed by carinate ridge in midline; antennal article 5 bears a small, rather than strong distomesial spine; the antennal scale overreaches article 5, instead of terminating at most at the midlength of that article; the P1 merus and carpus are dorsally almost spineless, instead of spinose; the P2–4 propodal flexor margins are distally convex, rather than nearly straight; the ultimate spine of the P2–4 dactyli is subequal to the penultimate, instead of distinctly smaller.

Uroptychus tuerkayi resembles U. maroccanus (see Baba & Macpherson 2017), and the above listed distinguishing characters between U. maroccanus and U. pauroptilus are partly applicable to between U. pauroptilus and U. tuerkayi . Uroptychus pauroptilus sp. nov. differs from U. tuerkayi as follows: the lateral orbital spine is small, rather than well developed; the excavated sternum is anteriorly convex, rather than sharply triangular; the eye is globular, as long as broad, instead of being 1.4–1.6 times longer; the antennal article 5 bears a tiny, rather than strong distomesial spine; the antennal scale overreaches the tip of, instead of terminating at most at the midlength of article 5; the antennal flagellum is long, exceeding far beyond the apex of rostrum, instead of being short, at most slightly overreaching the rostrum; the third maxilliped merus bears a few small but distinct spines distal to the midlength of the flexor margin, instead of being unarmed; the P1 merus and carpus are dorsally smooth, rather than spinose; the P2–4 meri are dorsally unarmed, rather than spinose; and the P2–4 propodal flexor margins are distally convex, rather than straight.

Unfortunately, molecular data for species of Uroptychus is scarce and any genetic comparison should be considered with caution. However, the new species is clustered with other species from the Western Pacific ( Fig. 1 View FIGURE 1 ), although with high genetic divergences ranging from 17 to 21%.

Distribution. Only known from the type locality, off Guinea Bissau, at 909 m.