Galathea inermis, 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 : 150-152

Galathea inermis n. sp.

( Fig. 52 )

Material examined. Holotype: Solomon Islands. SALOMON 1, Stn CP1802, 9°31.1’S, 160°35.0'E, 245–269 m, 2 October 2001: M 5.3 mm (MNHN-IU-2013-8316).

Paratypes: Solomon Islands. SALOMON 1, Stn CP1801, 9°25.0'S, 160°25.9'E, 264–273 m, 1 October 2001: 2 M 5.7–5.8 mm, 1 ov. F 4.8 mm (MNHN-IU-2013-8320).—Stn CP1802, 9°31.1'S, 160°35.0'E, 245–269 m, 2 October 2001: 1 M 4.2 mm (MNHN-IU-2013-8322); 1 M 4.8 mm (MNHN-IU-2013-8323); 1 ov. F 5.2 mm (MNHN-IU-2013-8321).—Stn CP1860, 9°22'S, 160°31'E, 620 m, 7 October 2001: 1 F 3.5 mm (MNHN-IU-2013- 8318). SALOMON 2, Stn CP2284, 8°37.29'S, 157°21.94'E, 195–197 m, 6 November 2004: 3 M 3.4–4.5 mm (MNHN-IU-2013-8317).—Stn CP2286, 8°39.54'S, 157°23.18'E, 248–253 m, 8 November 2004: 1 M 4.5 mm (MNHN-IU-2013-8319).

Etymology. From the Latin, inermis , unarmed, defenseless, in reference to the absence of spines on the dorsal carapace surface.

Description. Carapace: As long as broad. Cervical groove distinct, laterally bifurcated. Ridges with dense short setae, without long setae. Gastric region with 7 transverse ridges: 1 epigastric ridge medially interrupted, with 2 submedian spines; 2 protogastric ridges, anterior one medially interrupted, posterior ridge scale-like; third scalelike; 2 mesogastric ridges, anterior ridge uninterrupted, laterally not continuous to anteriormost branchial marginal spine; posterior ridge scale-like; 2 metagastric ridges successively shorter posteriorly, uninterrupted and not continuing with anterior branchial ridges. Anterior branchial region with distinct ridges. Mid-transverse ridge uninterrupted, preceded by cervical groove. Posterior branchial region with 6–8 transverse ridges, 2 or 3 of them uninterrupted; some additional scattered scales among ridges. Lateral margins subparallel, with 9 spines: 2 spines in front of and 7 spines behind anterior cervical groove; first anterolateral, well-developed, situated in frontal margin, second very small, accompanying another small spine ventral to between first and second; 3 spines on anterior branchial margin, and 4 spines on posterior branchial margin. External limit of orbit unarmed or ending in minute spine; infraorbital margin denticulate. Rostrum triangular, 1.8 times as long as broad, length 0.6 postorbital carapace length and breadth 0.3 that of carapace; dorsal surface nearly horizontal in lateral view, with small setiferous ridges; lateral margin with 5 relatively small (rarely 6), shallowly incised teeth.

Pterygostomian flap spineless on surface, with sparse short setae, anterior margin bluntly angular.

Sternun: Plastron about as long as broad, lateral extremities gently divergent posteriorly.

Abdomen: Somites 2–4 each with 2 uninterrupted and 2 interrupted transverse ridges on tergite, anterior ridge more distinctly elevated than posterior ridge; somites 5 and 6 with 2 medially interrupted ridges, posterior margin of somite 6 with distinct median lobe. Males with G1 and G2.

Eyes: Ocular peduncles 1.3 times longer than broad, maximum corneal diameter 0.8 rostrum width.

Antennula : Article 1 with 2 spines; well-developed distodorsal and distolateral spines; distomesial spine obsolescent. Ultimate article with tuft of fine setae on distodorsal margin.

Antenna: Article 1 hardly visible in dorsal view, with ventral distomesial spine exceeding distal margin of article 2. Article 2 with 2 subequal distal spines, not reaching midlength of article 3. Articles 3 and 4 unarmed.

Mxp3: Ischium with small spine on flexor distal margin; extensor margin with small but distinct distal spine; crista dentata with 20–21 denticles. Merus shorter than ischium; flexor margin with 2 strong subequal spines; extensor margin with distal spine. Carpus unarmed.

P1: 4.0 times carapace length, with setose scales and numerous long simple setae. Merus 1.8 times as long as carapace, 2.4 times as long as carpus, with small spines arranged roughly in rows, dorsomesial and ventromesial spines stronger, distal spines prominent. Carpus 0.7 length of palm, 3.0 times as long as broad; dorsal surface with some small spines arranged roughly in rows; mesial margin with 3 or 4 well-developed spines. Palm 3.8 times longer than broad, lateral and mesial margins subparallel; small spines arranged roughly in dorsolateral and dorsomesial rows. Fingers 0.8 length of palm each finger distally with two rows of teeth, spooned; opposable margins with blunt serration; fingers unarmed.

P2–4: moderately slender, with setose striae, and numerous long simple setae. P2 1.8 times carapace length. Meri successively shorter posteriorly (P3 merus 0.8 length of P2 merus, P4 merus 0.8 length of P3 merus; P2 merus 0.9 carapace length, 6.2 times as long as broad, 1.8 times longer than P2 propodus; P3 merus 4.4 times longer than broad, 1.6 times longer than P3 propodus; P4 merus 3.5 times as long as broad, 1.4 length of P4 propodus. Extensor margins with row of 14–17 proximally diminishing small spines on P2–3, 2 or 3 spines only on P4; lateral surface with 2 or 3 small spines on P4; flexolateral margin distally ending in strong spine followed proximally by several prominences. Carpi with 3 or 4 small spines on extensor margin on P2–3, 1 or 2 minute spines on P4; lateral surface with granules sub-paralleling extensor margin on P2–4; flexor distal margin with small distal spine. Propodi 5.0 (P2), 4.8 (P3), 4.0 (P4) times as long as broad; extensor margin unarmed; flexor margin with 5-6 slender movable spines on P2–4. Dactyli distally ending in well-curved strong spine, 0.5 length of propodi; flexor margin with 5 or 6 successively diminishing teeth, terminal one prominent.

Epipods on P1.

Remarks. Galathea inermis n. sp. is easily differentiated from the other closely related species, G. paulae n. sp. from Fiji and Tonga, and G. s a n c t a e Macpherson, 2012, from Vanuatu and New Caledonia, by the dfferent number of transverse ridges on the posterior branchial region, six to eight in G. i n er m i s, instead of four or five in the latter two species.

The genetic divergences among G. inermis and the other two species are higher than 17.4% ( G. paulae ) (COI) and 7.0% ( G. paulae ), 3.4% ( G. sanctae ) (16S rRNA) ( Tab. 3 ).

Distribution. Solomon Islands, 195– 620 m.

Figures

FIGURE 52. Galathea inermis n. sp., holotype, male, 5.3 mm, Solomon Islands (MNHN-IU- 2013 - 8316). 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, left P 1, dorsal view; F, right P 2, lateral view; G, right P 3, lateral view; H, right P 4, lateral view. Scale: A, F – H = 1 mm; E = 2 mm; B – D = 0.5 mm.