Uroptychus micrommatus, Baba, 2018

Baba, Keiji, 2018, Chirostylidae of the Western and Central Pacific: Uroptychus and a new genus (Crustacea: Decapoda: Anomura), Tropical Deep-Sea Benthos (Mémoires du Muséum national d'Histoire naturelle 212), pp. 1-612 : 312-319

Uroptychus micrommatus n. sp.

Figures 147-149

TYPE MATERIAL — Holotype: Indonesia, Tanimbar Islands . KARUBAR Stn CP 69, 8°42’S, 131°53’E, 356-368 m, 2.XI.1991, ♂ 8.2 mm ( MNHN-IU-2012-676 ) . Paratypes: Indonesia, Tanimbar Islands. KARUBAR Stn CC42, 07°53’S, 132°42’E, 354- 350 m, 28.X.1991, 1 ♂ 7.3 mm (MNHN-IU-2012-677) . – Stn CP69, 8°42’S, 131°53’E, 356-368 m, 2.XI.1991, 6 ♂ 3.4- 9.0 mm, 5 ov. ♀ 8.1-9.8 mm, 8 ♀ 3.7-10.2 mm (MNHN-IU-2012-675). Kai Islands. KARUBAR Stn CP09, 5°23’S, 132°29’E, 368-389 m, unidentified host, 23.X.1991, 1 ♂ 10.3 mm, 1 ov. ♀ 11.4 mm (MNHN-IU-2012-678) . Solomon Islands. SA- LOMON 2 Stn CP2262, 7°56.4’S, 156°51.2’E, 460-487 m, 3.XI.2004, 2 ♂ 4.3, 8.7 mm (MNHN-IU-2013-12295, MNHN- IU-2013-8576) . – Stn CP2263, 7°54.8’S, 156°51.3’E, 485-520 m, 3.XI.2004, 1 ♂ 9.2 mm (MNHN-IU-2013-8577) . – Stn CP2264, 7°52.4’S, 156°51.0’E, 515-520 m, 3.XI.2004, 1 ♂ 9.0 mm, 1 ov. ♀ 9.7 mm, 1 ♀ 6.9 mm (MNHN-IU-2013-8578).

ETYMOLOGY„ From the Greek mikrommatos (small-eyed), alluding to the eye cornea much smaller than the remaining eyestalk, a character to separate the species from U. occultispinatus Baba, 1988 .

DISTRIBUTION„ Indonesia (Kai and Tanimbar Islands) and Solomon Islands; 354- 520 m.

SIZE„ Males, 3.4-10.3 mm; females, 3.7-11.4 mm; ovigerous females from 8.1 mm.

DESCRIPTION„ Large species. Body and appendages covered with setae. Carapace: Slightly broader than long (0.9 × as long as broad). Dorsal surface slightly convex from anterior to posterior, bearing distinct groove between gastric and cardiac regions, and anterior and posterior branchial regions; covered with scale-like short ridges (somewhat elevated in large specimens, very weak in small specimens) supporting setae, bearing tiny tubercles or denticles, usually on anterior gastric region; greatest breadth 1.5-1.9 × (usually 1.7 x) distance between anterolateral spines. Lateral margins convex, with distinct spines: first anterolateral spine well developed, overreaching lateral orbital spine, followed by 1 or 2 spinules often obsolete on hepatic margin; second spine situated at anterior end of anterior branchial margin, as large as anterolateral spine, followed by 1 or 2 spines usually very small, occasionally of good size or obsolete; third spine located at anterior end of posterior branchial margin, stronger than second spine, followed by 3 distinct spines, posteriormost usually small, rarely obsolete, followed by ridge along lateral margin. Rostrum triangular, with interior angle of 27-30 °; dorsal surface somewhat concave; lateral margin rarely with very small subapical spine; length 0.4-0.5 × that of carapace, breadth about half carapace breadth at posterior carapace margin. Lateral orbital spine very small, moderately remote from and slightly anterior to level of anterolateral spine. Pterygostomian flap anteriorly angular, produced to small spine, surface granulose.

Sternum: Excavated sternum having anterior margin strongly convex between bases of Mxp1, surface with low ridge in midline. Sternal plastron slightly broader than long. Sternite 3 depressed well, anterolateral angle sharply produced; anterior margin representing broad V-shape, with U-shaped or semicircular median sinus flanked by very small, obsolescent spine. Sternite 4 having straight or slightly convex, smooth anterolateral margin anteriorly blunt angular, often bearing a few denticles, 1.3-1.6 × longer than posterolateral margin. Sternite 5 slightly broader than sternite 4, anterolateral margins strongly convex anteriorly, 1.0-1.3 × length of posterolateral margin of sternite 4. Sternite 6 broadest; sternite 7 narrower than sternite 6.

Abdomen: Somite 1 antero-posteriorly strongly convex. Somite 2 tergite 2.6-2.9 × broader than long; pleural lateral margin weakly concave and weakly divergent posteriorly, posterolateral end blunt. Pleuron of somite 3 with blunt lateral margin. Telson half as long as broad; posterior plate concave or emarginate on posterior margin, usually 1.2-1.3 × longer than (rarely subequal to) anterior plate.

Eye: Elongate (1.7 × longer than broad), markedly narrowed distally, terminating in midlength of rostrum. Cornea small, less than half length of remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle relatively slender, 3.1-3.5 × (2.6 × in small specimens) longer than high. Antennal peduncle extending far beyond cornea, barely reaching apex of rostrum. Article 2 with small but distinct distolateral spine. Antennal scale tapering, relatively broad basally, more than 2 × broader than article 5, overreaching article 5. Article 4 with strong distomesial spine. Article 5 about twice as long as article 4, breadth 0.6 × height of ultimate article of antennule; with strong distomesial spine. Flagellum of 18-20 segments reaching distal end of P1 merus (15 segments overreaching P1 merus by distal 7 segments in smallest specimen).

Mxp: Mxp1 with bases broadly separated. Mxp3 basis with 1 distal denticle usually obsolescent, often absent on mesial ridge. Ischium with distally rounded flexor margin, crista dentata with numerous (34-40) denticles. Merus broad relative to length, 1.6 × longer than ischium, flattish on mesial face; distolateral spine small; flexor margin ridged, with a few small, distinct spines distal to point one-third from distal end. Distolateral spine of carpus small or obsolescent.

P1: Massive, setose, length 3.4-3.7 × that of carapace. Ischium dorsally with relatively short, basally broad, depressed spine, ventrally with tubercular processes along mesial margin, with subterminal spine almost vestigial or obsolete. Merus and carpus somewhat tuberculose, each with distomesial and distolateral spines ventrally; additional short spines along mesial margin of merus. Merus 0.8-0.9 × as long as carapace. Carpus 1.0 × (small specimens)-1.2 × length of merus. Palm 2.2-2.7 × longer than broad, 1.2-1.4 × longer than carpus. Fingers directed somewhat laterally in large specimens, not gaping, distally crossing. Movable finger 0.4 × as long as palm (slightly more than half as long in small specimens), opposable margin with low median process proximal to position of opposite low eminence on fixed finger.

P2-4: Relatively setose. Meri with setiferous short rugae, successively shorter posteriorly (P3 merus 0.9-1.0 × length of P2 merus, P4 merus 0.9 × length of P3 merus), P2 and P3 meri subequally broad, P4 merus slightly narrower than P3 merus; dorsal margin with several eminences. P2 merus 0.7-0.8 length of carapace, subequal to length of P2 propodus; P3 merus 0.9 × length of P3 propodus; P4 merus 0.7-0.8 × length of P4 propodus; length-breadth ratio, 3.5-3.7 on P2, 3.1-3.3 on P3, 3.0-3.4 on P4. Carpi successively slightly shorter posteriorly (P3 carpus 0.9-1.0 × length of P2 carpus, P4 carpus 0.9-1.0 × length of P3 carpus); carpus-propodus length ratio, 0.4-0.5 on P2, 0.4 on P3, 0.3-0.4 on P4. Propodi successively longer posteriorly or shorter on P2 than on P3 and P4 and subequal on P3 and P4; flexor margin slightly concave in lateral view, ending in pair of spines preceded by 2-3 movable spines on P2, 1-3 spines on P3 and P4. Dactyli proportionately broad, about half as long as propodi (slightly more than half as long in small specimens); dactylus-carpus length ratio, 1.0-1.1 (1.3-1.4 in small specimens) on P2, 1.1-1.2 (1.4-1.5 in small specimens) on P3, 1.4 (1.5-1.7 in small specimens) on P4; flexor margin slightly curving, with 10-16 spines obscured by thick setae, ultimate slender, usually slightly longer than penultimate and distinctly longer than antepenultimate; penultimate spine slightly more than 2 × as broad as antepenultimate, remaining proximal spines slender and obliquely directed, close to one another but not contiguous.

Eggs. More than 100 eggs carried; diameter, 1.2 mm.

REMARKS — The granules and setiferous scale-like ridges on the carapace dorsal surface are pronounced in large specimens, less so or not discernible in small specimens. The hepatic marginal spines are obsolescent in small specimens. The sternal plastron has the anterior margin with a median notch flanked by a spine usually very small, occasionally obsolescent or totally absent ( Figure 149 ).

Small populational differences are observed. The Indonesian specimens (poc, 4.2-8.9 mm) differ from the Solomon Islands specimens (poc, 3.4-11.0 mm) in the following particulars: the antennular ultimate article is higher relative to length (the length-height ratio 2.6-3.4 versus 3.5-4.6); the P1 merus is broader, with the length-breadth ratio 0.8-0.9 versus 1.1-1.3 (the length measured in ventral midline, the breadth measured at midlength), the P1 merus-carapace length ratio being 0.8-0.9 versus 1.0. These differences are regarded here as intraspecific variations for the time being, awaiting molecular data (analyses using specimens of MNHN-IU-2012-677 and MNHN-IU-2012-12295 have failed (L. Corbari, personal. comm.).

Uroptychus micrommatus resembles U. occultispinatus Baba, 1988 (replacement name for U. granulatus var. japonicus Balss, 1913a ) from Japan and the Philippines in nearly all aspects, but they key out in remotely different couplets due to the presence or absence of median notch and/or submedian spines on the anterior margin of sternite 3. Uroptychus micrommatus is characterized by eyes that are strongly narrowed distally rather than uniformly broad as in U. occultispinatus ( Figure 150B ; Balss 1913b: fig. 18). The P1 ischium in U. micrommatus has no distinct subterminal spine on the ventromesial margin, whereas the spine is short and distinct in U. occultispinatus ( Figure 150E ).

Uroptychus micrommatus resembles U. dentatus Balss, 1913 from the western Indian Ocean and U. crassipes Van Dam, 1939 (see above) in the carapace ornamentation, and in having relatively massive P1 and in the spination of the P2-4 dactyli. The shape of the sternal plastron, especially the median excavation of the anterior margin in U. dentatus is variable as illustrated ( Figure 151 ) for a female (6.1 mm) of the syntypes of U. dentatus from Valdivia Station 264 in 1079 m (Musée Zoologique, Strasbourg, MZS 349) and for the material reported by Baba (1990) from Madagascar. This variability is similar to that in the present material of U. micrommatus n. sp. ( Figure 150 ). However, U. dentatus differs from U. micrommatus in having the Mxp3 merus unarmed instead of bearing a few distinct spines as in U. micrommatus . In addition, the eyes of U. dentatus are not narrowed distally, and the anterolateral margin of sternite 4 is slightly longer than the posterolateral margin, instead of being much longer (1.3-1.6 times longer) as in U. micrommatus .

Uroptychus micrommatus can be separated from U. crassipes by the following differences: the rostral lateral margin is smooth instead of bearing a distinct subapical spine on each side; the eyes are distally narrowed even in small specimens rather than having the lateral and mesial margins subparallel; the P1 ischium has a reduced instead of well-developed subterminal spine on the ventromesial margin; and the P1 merus and carpus each bear almost vestigial instead of distinct spines on the dorsoterminal margin.

Figures

FIGURE 147 Uroptychus micrommatus n. sp.,holotype,male 8.2 mm (MNHN-IU-2012-676).A, carapace and abdomen,setae omitted from left half,proximal part of P1 included,dorsal.B, same,lateral.C, sternal plastron,with excavated sternum and basal parts of Mxp1.D, telson.E, left antenna,ventral. F, left Mxp3, distal articles omitted, ventral.G, same, merus and carpus, setae omitted, lateral.Scale bars:A,B;5 mm; C-G,1 mm.

FIGURE 148 Uroptychus micrommatus n. sp.,holotype,male 8.2 mm (MNHN-IU-2012-676). A, right P1, proximal part,ventral. B, right P1, dorsal.C, left P2,lateral. D, same, distal part, setae omitted. E, left P3, setae omitted, lateral.F, left P4, setae omitted, lateral.G, same, distal part, setae omitted. Scale bars: A,B,5 mm; C-G,1 mm.

FIGURE 149 Uroptychus micrommatus n.sp.,A-C, carapace,dorsal.D-G, anterior part of sternal plastron.A,paratype,female 3.7 mm (MNHN-IU-2012-675).B,paratype, female 8.7 mm (MNHN-IU-2012-675).C, paratype,female 10.3 mm (MNHN-IU-2012-675).D, paratype,male 10.3 mm (MNHN-IU-2012-675).E, paratype, female 9.0mm (MNHN-IU-2012-675).F, paratype,female 8.0 mm (MNHN-IU-2012-675).G,paratype,female 3.7 mm (MNHN-IU-2012-675).Scale bars:1mm.

FIGURE 150 Uroptychus occultispinatus Baba, 1988, ovigerous female 6.9 mm from Albatross Stn 5529 (USNM 150308). A, carapace and anterior part of abdomen, lateral. B, anterior part of carapace, dorsal.C, anterior part of sternal plastron. D, right Mxp3, ventral. E, right P1, proximal part, ventral.F, right P2,lateral.G, same, distal part, setae omitted,lateral.H, right P3, lateral.I, right P4, lateral.Scale bars:1 mm.

FIGURE 151 Uroptychus dentatus Balss, 1913. A, D, G-J, syntype, female 6.1 mm (MZS 349); B, female 5.2 mm from Madagascar, Vauban Stn CH 104 (MNHN-IU-2014-12825);C,male 9.0 mm,Vauban StnCH 104 (MNHN-IU-2014-12825);E,same;F,female 5.2(MNHN-IU-2014-12825).A-C, carapace. D-F, anterior part of sternum.G, right antenna.H, left Mxp3,lateral.I, right P2,lateral.J, same,distal part.Scale bars:A-C,E,5 mm;D,F-I,J,1 mm.