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
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Galathea psila n. sp.
( Fig. 91View FIGURE 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.
Mxp 3: 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.
P 1: missing.
P 2–4: moderately short and slender, with some setose striae and some long plumose and non-plumose setae, some of them iridescent. P 2 1.6 times carapace length. Meri successively shorter posteriorly (P 3 merus 0.9 length of P 3 merus, P 4 merus 0.9 length of P 3 merus); P 2 merus 0.6 carapace length, 3 times as long as broad, 1.3 times longer than P 2 propodus. P 3 merus 2.9 times as long as broad, 1.2 times longer than P 3 propodus. P 4 merus 2.8 times as long as broad, 1.1 times longer than P 4 propodus. Extensor margin with row of 8 or 9 proximally diminishing spines on P 2–4; ventral margins distally ending in strong spine, lateral sides unarmed; ventromesial margin with terminal spine on P 2–4. Carpi with 5–7 spines on extensor margin on P 2–4; lateral surface with 4 or 5 small spines sub-paralleling extensor margin; flexor distal margin blunty produced. Propodi 3.3 (P 2), 4.0 (P 3) 3.4 (P 4) 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 P 1.
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 Mxp 3 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 % (16 S 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 % (16 S rRNA) ( Tab. 3).
Distribution. New Caledonia, 274 m.
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