Galathea psila, Macpherson, Enrique & Robainas-Barcia, Aymee, 2015

Macpherson, Enrique & Robainas-Barcia, Aymee, 2015, Species of the genus Galathea Fabricius, 1793 (Crustacea, Decapoda, Galatheidae) from the Indian and Pacific Oceans, with descriptions of 92 new species, Zootaxa 3913 (1), pp. 1-335 : 254-255

Galathea psila n. sp.

( Fig. 91 )

Material examined. Holotype: New Caledonia. CHALCAL 2, Stn CP18, 24°47.00'S, 168°09.43'E, 274 m, 27 October 1986: ov. F 3.4 mm (MNHN-IU-2013-8303).

Etymology. From the Greek, psilos, bare, smooth, in reference to the absence of spines on the dorsal carapace surface.

Description. Carapace: Slightly longer than broad; transverse ridges on dorsal surface with dense short setae, and some scattered long non-plumose iridescent setae; cervical groove distinct, laterally bifurcated. Gastric region unarmed, with 5 transverse ridges: 1 epigastric ridge, unarmed, medially interrupted; 1 protogastric ridge medially interrupted; 1 mesogastric ridge, scale-like and 1 median scale between protogastric and mesogastric ridges; 2 metagastric ridges, anterior ridge medially interrupted, not extending laterally to anteriorbranchial region, posterior ridge short. Anterior branchial region with distinct ridges. Mid-transverse ridge uninterrupted, preceded by shallow cervical groove. Posterior branchial region with 5 transverse ridges, 2 ridges uninterrupted. Lateral margins slightly convex medially, with 5 spines: 1 spine in front of and 4 spines behind anterior cervical groove; first anterolateral, well-developed, clearly behind level of lateral limit of orbit, 1 spine ventral to between first and anterior branch of cervical groove; 2 spines on anterior branchial region, and 2 spines on posterior branchial margin. Minute spine on limit of orbit; infraorbital margin with well-developed spine. Rostrum 1.5 times as long as broad, length 0.7 postorbital carapace length and breadth 0.4 that of carapace; distance between distalmost lateral incisions 0.3 distance between proximalmost lateral incisions; dorsal surface longitudinally concave, with numerous some small setae; lateral margin with 4 deeply incised sharp teeth.

Pterygostomian flap rugose, unarmed, ridges with short setae, anterior margin acute.

Sternum: 0.8 times as long as broad, lateral extremities gently divergent posteriorly.

Abdomen: Somite 2 with 2 uninterrupted transverse ridges on tergite; somite 3–4 with anterior ridge only, and some scattered scales; somites 5–6 smooth.

Eyes: Ocular peduncles 1.4 times longer than broad, maximum corneal diameter 0.5 rostrum width.

Antennule: Article 1 with 3 well-developed distal spines, distodorsal larger than others. Ultimate article twice longer than wide, with a few fine setae not in tuft on distodorsal margin.

Antenna: Article 1 with strong distomesial spine reaching distal margin of article 2. Article 2 with 2 subequal distal spines, and barely reaching midlength of article 3. Articles 3 and 4 unarmed.

Mxp3: Ischium with flexor margins ending in small spine, extensor margin ending in acute angle; crista dentata with 22 denticles. Merus shorter than ischium; flexor margin with 2 strong subequal spines; extensor margin with distal spine. Carpus unarmed.

P1: missing.

P2–4: moderately short and slender, with some setose striae and some long plumose and non-plumose setae, some of them iridescent. P2 1.6 times carapace length. Meri successively shorter posteriorly (P3 merus 0.9 length of P3 merus, P4 merus 0.9 length of P3 merus); P2 merus 0.6 carapace length, 3 times as long as broad, 1.3 times longer than P2 propodus. P3 merus 2.9 times as long as broad, 1.2 times longer than P3 propodus. P4 merus 2.8 times as long as broad, 1.1 times longer than P4 propodus. Extensor margin with row of 8 or 9 proximally diminishing spines on P2–4; ventral margins distally ending in strong spine, lateral sides unarmed; ventromesial margin with terminal spine on P2–4. Carpi with 5–7 spines on extensor margin on P2–4; lateral surface with 4 or 5 small spines sub-paralleling extensor margin; flexor distal margin blunty produced. Propodi 3.3 (P2), 4.0 (P3) 3.4 (P4) times as long as broad; extensor margin with 5–7 proximal spines; flexor margin with 4–6 slender movable spines. Dactyli distally ending in well-curved strong spine, length 0.6–0.7 that of propodi; flexor margin with 5 proximally diminishing teeth, terminal one prominent.

Epipods present on P1.

Remarks. The new species resembles G. bimaculata Miyake & Baba, 1966 from Japan to New Caledonia and Western Australia, from which it can be distinguished by the following characters:

- The extensor margin of the Mxp3 merus is unarmed in G. bimaculata , whereas one distal spine is always present in G. p s i l a.

- The gastric region has all ridges scale-like or concentric arcs in G. bimaculata , whereas the protogastric ridge is transverse and medially interrupted in G. p s i l a.

The genetic divergence with G. bimaculata is 17.8% (COI) and 12.7% (16S rRNA) ( Tab. 3 ). Galathea psila is also related to G. ploto n. sp. from New Caledonia from which it can be distinguished by the absence of epigastric and hepatic spines in G. p s i l a, whereas these spines are present in G. ploto . The genetic divergence with G. p l o t o is 18.8% (COI) and 13.1% (16S rRNA) ( Tab. 3 ).

Distribution. New Caledonia, 274 m.

Figures

FIGURE 91. Galathea psila n. sp., holotype, ovigerous female, 3.4 mm, New Caledonia (MNHN-IU- 2013 - 8303). A, carapace and abdomen, dorsal view; B, thoracic sternites 3 and 4; C, left part of cephalothorax, ventral view, showing antennular and antennal peduncles, and anterior part of pterygostomian flap; D, ischium, merus and carpus of right Mxp 3, lateral view; E, right P 2, dorsal view; F, left P 3, lateral view; G, right P 4, lateral view. Scale: A, E, F, G = 1 mm; B – D = 0.5 mm.