Uroptychus plumella, 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 : 404-407

Uroptychus plumella n. sp.

Figures 199 , 200

TYPE MATERIAL — Holotype: New Caledonia, Loyalty Ridge. BATHUS 3 Stn DW 778, 24°43’S, 170°07’E, 750-760 m, 24.XI.1993, 1 ov. ♀ 6.6 mm ( MNHN-IU-2012-683 ).

ETYMOLOGY„ The specific name is a noun in apposition from the Latin plumella , diminutive of pluma (= soft feather), alluding to short soft plumose setae covering carapace and pereopods.

DISTRIBUTION„ Loyalty Ridge, 750- 760 m.

DESCRIPTION„ Small species. Carapace: 1.3 × broader than long (0.8 × as long as broad), broadest on posterior fourth; greatest breadth 2.1 × distance between anterolateral spines. Dorsal surface convex smoothly from anterior to posterior and from side to side, without depression, thickly covered with short fine plumose setae. Lateral margins convexly divergent, finely granulose, and weakly ridged along posterior fourth; anterolateral spine distinctly larger than lateral orbital spine, directed forward. Rostrum horizontal in proximal three-quarters, upcurved in distal quarter, narrow triangular, with interior angle 22°; dorsal surface somewhat concave; lateral margin straight with 1 (right) or 3 (left) vestigial denticles distally; length half that of remaining carapace, breadth one-third carapace breadth at posterior carapace margin. Lateral orbital angle acuminate, situated directly mesial to and separated from anterolateral spine by basal breadth of latter spine. Pterygostomian flap smooth on surface, anteriorly angular, produced to small spine; anterior half 1.3 × higher than posterior half.

Sternum: Excavated sternum with convex anterior margin, surface with weak low ridge in midline. Sternal plastron 0.7 × as long as broad; lateral extremities divergent posteriorly. Sternite 3 shallowly depressed; anterior margin deeply emarginate, medially V-shaped, without submedian spines. Sternite 4 with anterolateral margin convex and denticulate, about 2 × longer than posterolateral margin. Anterolateral margin of sternite 5 anteriorly convex and denticulate, 1.3 × longer than posterolateral margin of sternite 4.

Abdomen: Somite 1 somewhat convex from anterior to posterior, without transverse ridge. Somite 2 tergite 2.6 × broader than long; pleural lateral margin concavely divergent posteriorly, posterolateral end blunt. Pleuron of somite 3 laterally blunt. Telson 0.4 × as long as broad; posterior plate slightly longer than anterior plate, emarginate on posterior margin.

Eye: 1.4 × longer than broad, not reaching midlength of rostrum, mesial and lateral margins subparallel. Cornea not inflated, slightly shorter than remaining eyestalk.

Antennule and antenna: Ultimate article of antennule 4.2 × longer than high. Antennal peduncle overreaching cornea, overreaching midlength of rostrum. Article 2 distolaterally acuminate, lacking distinct spine. Antennal scale 2.2 × broader than article 5, extending slightly beyond proximal second segment of flagellum and greatly overreaching eye. Articles 4 and 5 each with tiny distomesial spine (that of article 4 tubercle-like), article 5 1.4 × longer than article 5, breadth 0.6 × height of antennular ultimate article. Flagellum of 16 segments reaching distal margin of P1 merus.

Mxp: Mxp1 with bases moderately separated. Mxp3 with relatively long plumose setae other than brushes on distal articles. Basis having mesial ridge nearly smooth. Ischium with flexor margin not rounded distally; crista dentata with denticles widely spaced along most of length, minute and closely set on distal part. Merus 2.2 × longer than ischium, flexor margin roundly ridged, with 4 tiny spines or processes along distal third. Distodorsal spine on each of merus and carpus.

P1: 4.5 × longer than carapace, sparingly covered with relatively short fine plumose setae. Ischium with small dorsal spine, ventromesial margin with row of denticle-like spines, lacking distinct subterminal spine. Merus with small distomesial and distolateral spines, row of denticles along distodorsal margin, granulate along proximal mesial margin; length 0.9 × that of carapace. Carpus subcylindrical, 1.5 × longer than merus, distodorsal margin with small but distinct median spine flanked by denticles. Palm 3.7 × longer than broad, 1.1 × longer than carpus. Fingers moderately depressed and relatively broad, distally incurved, crossing when closed, not gaping; fixed finger with low process at midlength of opposable margin; movable finger half as long as palm, opposable margin with larger process proximal to position of opposite process on fixed finger.

P2-4: Relatively broad and somewhat compressed mesio-laterally, with fine soft setae. Meri slightly shorter on P3 than on P2, much shorter on P4 than on P3 (P4 merus 0.8 length of P3 merus); breadths slightly smaller on P2 than on P3 and P4; length-breadth ratio, 3.6 on P2, 3.2 on P3, 2.5 on P4; dorsal margins rounded, not cristiform, with a few spines very tiny on proximal half on P2 and P3, obsolescent on P4. P2 merus 0.7 × as long as carapace, 1.0 × (left) or 0.9 × (right) length of P2 propodus; P3 merus 0.8 × (left) or 1.0 × (right) length of P3 propodus; P4 merus 0.6 × length of P4 propodus. Carpi successively shorter posteriorly; carpus-propodus length ratio, 0.6 on P2, 0.4 (left) or 0.5 (right) on P3, 0.5 on P4. Propodi shortest on P2, longer and subequal on P3 and P4; flexor margin moderately convex on distal portion, ending in pair of terminal spines preceded by 8, 7, 6 spines on P2, P3, P4 respectively. Dactyli shortest on P2, subequal on P3 and P4; moderately curving; dactylus-carpus length ratio, 0.7, 0.7-0.8, 1.1 on P2, P3, P4 respectively; flexor margins with 7, 8, 8 strong, proximally diminishing, obliquely directed spines on P2, P3, P4 respectively.

Eggs. Five eggs carried; size, 1.29 × 1.13 mm - 1.33 × 1.25 mm.

REMARKS — Uroptychus plumella n. sp. is characterized, along with U. senticarpus n. sp. and U. shanei n. sp., by the combination of the following characters: the carapace longer than broad, laterally unarmed other than the anterolateral spine; sternite 3 with the anterior margin emarginate in a broad V-shape; P1 nearly spineless, with the fingers distally strongly incurved; the P2-4 dactyli ending in a strong spine preceded by similar, proximally diminishing spines. However, the plumose setae on the carapace and P1 as displayed by this species are not possessed by the two related species. Characters to distinguish these species are outlined under the accounts of the related species (see below).

Figures

FIGURE 199 Uroptychus plumella n.sp.,holotype,ovigerous female 6.6 mm (MNHN-IU-2012-683).A, carapace and anterior part of abdomen,proximal part of left P1 included,dorsal.B, same,setae on carapace omitted,lateral.C, lateral margin of carapace,dorsolateral.D, sternal plastron, with excavated sternum and basal parts of Mxp1.E, telson.F, left antenna,ventral.G,right Mxp3,ventral.H,same,lateral.Scale bars:1 mm.

FIGURE 200 Uroptychus plumella n.sp.,holotype,ovigerous female 6.6 mm (MNHN-IU-2012-683).A, left P1,proximal part,setae omitted,ventral.B, same,distal three articles,dorsal.C, same, fingers, setae omitted, ventral. D, left P2, lateral. E, same, distal part, setae omitted, lateral.F, left P3, setae omitted, lateral.G, left P4, setae omitted, lateral.H, same,distal part,setae omitted, lateral. Scale bars: 1 mm.