Leiogalathea sinon, Rodríguez-Flores & Macpherson & Machordom, 2019

Rodríguez-Flores, Paula C., Macpherson, Enrique & Machordom, Annie, 2019, Revision of the squat lobsters of the genus Leiogalathea Baba, 1969 (Crustacea, Decapoda, Munidopsidae) with the description of 15 new species, Zootaxa 4560 (2), pp. 201-256 : 247-249

Leiogalathea sinon n. sp.

( Figs. 11H , 19 )

Type material. Holotype: Tonga. BORDAU 2 Stn CP 1539, 21°36.75'S, 175°19.37'W, 558–586 m, 5 June 2000: F 8.3 mm (MNHN-IU-2014-13711).

Paratype: French Polynesia. TARASOC Stn DW3435 , 16°41'S, 151°02'W, 500–612 m, 15 October 2009: 1 M 3.2 mm (MNHN-IU-2014-13719) .

Etymology. From the name Sinon, the Greek youth who persuades the Trojans to take in the wooden horse. The name is considered a substantive in apposition.

Description. Carapace: 1.2–1.3 × as long as broad. Mid-transverse ridge usually interrupted, preceded by deep cervical groove, followed by 6 or 7 laterally interrupted transverse ridges. Lateral margins slightly convex, with 4 distinct spines: first spine anterolateral, well-developed; hepatic margin unarmed; second and third spines on anterior branchial margin, and fourth spine on posterior branchial margin. Rostrum horizontal, dorsally flattish or slightly concave, 1.4–1.6 × as long as broad, length 0.3 × and breadth 0.2–0.3 × that of carapace; lateral margin with 6–8 rudimentary teeth.

Sternum: Sternite 3 broad, 3.0–3.5 × as wide as long, anterolaterally produced, anterior margin with shallow median notch flanked by 2 shallow denticulate lobes. Sternite 4 broadly contiguous to sternite 3; surface depressed in midline, smooth; greatest width 2.2 × that of sternite 3, 2.8 × as wide as long.

Abdomen: Tergite 2 with 2 elevated transverse ridges, tergites 3–4 each with transverse ridge, tergites 5–6 smooth; tergite 6 with transverse posteromedian margin.

Eye: Ocular peduncle, slightly longer than wide; cornea subglobular, maximum corneal diameter 0.8 × rostrum width, as wide as eyestalk.

Antennule: Article 1 with distomesial angle minutely serrated; lateral margin serrated.

Antenna: Article 1 with strong distomesial spine not reaching mid-length of article 2; article 2 with strong distomesial spine larger than distolateral and overreaching end of article 3; articles 3 and 4 unarmed.

Mxp3: Ischium as long as merus measured along extensor margin; flexor margin sharply ridged, terminating in well-developed spine; extensor margin unarmed; crista dentata finely denticulate; merus flexor margin with strong median spine and with or without distal spine, extensor margin with distal spine.

P1: 2.8 (male), 2.5 (female) × carapace length, with numerous short striae, and scattered uniramous long setae on merus to dactylus. Merus 0.7 length of carapace, 2.1 × as long as carpus, with strong mesial and distal spines, and scattered dorsal spines. Carpus slightly shorter than palm, 1.6 × as long as broad, dorsal surface with scattered spines, mesial margins with 3 or 4 strong spines (distal second strongest), lateral margin unarmed. Palm, 2.1 × as long as broad, armed with spines in irregular longitudinal rows on mesial and lateral margins, dorsal surface unarmed. Fingers 1.3 × as long as palm; fixed finger with row of spines along lateral margin; movable finger with well-developed proximal mesial spine.

P2–4: Slender, somewhat compressed laterally, with short setiferous striae on dorsal surface; with sparse long and thick setae on ischium to dactylus. Meri successively shorter posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus 0.9 × length of P3 merus). P2 merus 0.6 × carapace length, 7.2 × as long as broad, 1.2 × as long as P2 propodus; P3 merus 5.7 × as long as broad, 1.2 × as long as P3 propodus; P4 merus 5.6 × as long as broad, 1.3 × as long as P4 propodus; extensor margins with row of 9–12 proximally diminishing spines on P2–4; lateral surface unarmed on P2–3, with several dorso-extensor spines in P4; flexor margin with well-developed distal spine and several additional projecting scales. Carpi with 4–6 spines on extensor margin on P2–3, unarmed on P4, lateral side smooth; flexor margin with small distal spine. Propodi 9.4–11 × as long as broad on P2–4, flexor margin with 6–9 movable spinules on. Dactyli slender, 0.6–0.7 × length of propodi; distal claw short, moderately curved; flexor margin nearly straight, with 8–10 small teeth decreasing in size proximally, each with slender movable spinule, ultimate tooth closer to penultimate tooth than to base of distal claw.

Colour in life. Unknown

Genetic data. COI and 16S ( Table 2).

Distribution. Tonga and Polynesia, from 500 to 612 m.

Remarks. Leiogalathea sinon belongs to the group of species having the hepatic margin of the carapace unarmed and the branchial margin armed with 3 spines. The species is morphologically very similar to L. pallas from New Caledonia, Papua New Guinea, Vanuatu, Chesterfield Islands and Solomon Islands. However, L. sinon can be distinguished from that species by following differences: Leiogalathea pallas has the lateral margin of the rostrum serrated, whereas this margin has 6–8 rudimentary teeth in L. sinon ; the distomesial spine on the antennal article 1 overreaches the article 2 in L. pallas , whereas this spine barely reaches the article 2 in L. sinon ; the anterior margin of sternite 4 is broadly contiguous with sternite 3 in L. sinon , and narrowly contiguous in L. pallas .

The two species are clearly different genetically, with the average divergence of 6.9% and 13% for 16S and COI respectively.

Figures

FIGURE 11. Rostrum, and ocular peduncle, dorsal view. A, Leiogalathea evander n. sp., holotype, M 3.9 mm (MNHN-IU- 2015-820). B, L. imperialis (Miyake & Baba, 1967), holotype, ov. F 5.2 mm (BLIH 205a). C, L. juturna n. sp., holotype, F 4.2 mm (MNHN-IU-2013-17404). D, L. laevirostris (Balss, 1913), syntype, F 4.9 mm (ZMB17488). E, L. pallas n. sp., holotype, F 6.9 mm (MNHN-IU-2014-13395). F, L. paris n. sp., holotype, ov. F 4.0 mm (MNHN-IU-2011-4471). G, L. priam n. sp., holotype, M 5.0 mm (MNHN-IU-2014-13697). H, L. sinon n. sp., holotype, F 8.3 mm (MNHN-IU-2014-13711). I, L. turnus n. sp., holotype, M 8.0 mm (MNHN-IU-2014-13744). Scale = 1 mm.

FIGURE 19. Leiogalathea sinon n. sp., holotype, F 8.3 mm, Tonga (MNHN-IU-2014-13711). A, carapace and abdomen, dorsal view. B, sternites 3–4. C, cephalic region, showing antennular and antennal peduncles, ventral view. D, right Mxp3 ischium and merus, lateral view. E, right P1, dorsal view. F, right P2, lateral view. G, dactylus of right P2, lateral view. H, left P3, lateral view. I, left P4, lateral view. Scales: A, E, F, H, I = 2.0 mm; B–D, G = 1.0 mm.