Galathea gnoma, 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 : 128-130

Galathea gnoma n. sp.

( Fig. 43 )

Material examined. Holotype: Indonesia. Kei Islands. KARUBAR, Stn DW30, 05°39'S, 132°56'E, 111–118 m, 26 October 1991: M 2.7 mm (MNHN-IU-2013-13513).

Paratypes: Vanuatu. MUSORSTOM 8, Stn CP1131, 17°52.95'S, 168°33.11'E, 140–175 m, 29 September 1994: 1 M 3.5 mm (MNHN-IU-2013-13952); 1 ov. F 3.2 mm (MNHN-IU-2013-13953). SANTO, Stn EP36, 15°33.1–33.3'S, 167°12.4–12.7'E, 20–60 m, 15 October 2006: 2 M 2.4–2.6 mm, 2 F 2.4–2.5 mm (MNHN-IU- 2013-13985).

Etymology. From the Latin gnomus, dwarf, in reference to the small size of the species.

Description. Carapace: Slightly longer than broad; transverse ridges with dense short setae, with scattered long non-iridescent setae; cervical groove distinct, laterally bifurcated. Gastric region with 5 transverse ridges: 1 epigastric ridge medially interrupted, with 2 spines; 2 protogastric ridges, anterior ridge medially interrupted (uninterrupted in paratypes), with posterior median arcuate scale-like ridge, and 1 small parahepatic spine on each side; 1 mesogastric ridge medially uninterrupted or medially interrupted, not continuing laterally with anteriormost branchial spines; 2 metagastric ridges, anterior ridge uninterrupted, not continuing laterally to anterior branchial ridges, posterior one short. Anterior branchial region with distinct ridges. Mid-transverse ridge uninterrupted, preceded by shallow cervical groove, followed by 4 ridges, 1 or 2 of them uninterrupted. Lateral margins slightly convex, with 6 spines: 2 spines in front of and 4 spines behind anterior cervical groove; first anterolateral, welldeveloped, at same level of lateral limit of orbit, second very small, with spine ventral to between first and second spines; 2 spines on anterior branchial region, and 2 spines on posterior branchial margin. Lateral limit of orbit with small spine; infraorbital margin with strong spine. Rostrum narrowly triangular, 1.9–2.0 as long as broad, length 0.7 carapace length and breadth 0.4 that of carapace; distance between distalmost lateral incisions 0.25 distance between proximalmost lateral incisions; dorsal surface nearly horizontal in lateral view, with some short setae; lateral margin with 4 deeply incised sharp teeth.

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

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

Abdomen: Somites 2–3 with 2 transverse uninterrupted ridges; somite 4 with anterior ridge only; somites 5–6 smooth; posteromedian margin of somite 6 straight. Males with G1 and G2.

Eyes: Ocular peduncles 1.5 times longer than broad, maximum corneal diameter 0.7 rostrum width.

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

Antenna: Article 1 with ventral distomesial spine reaching distal margin of article 2. Article 2 with distolateral spine longer than distomesial, reaching midlength of article 3. Article 3 with small distomesial spine. Article 4 unarmed.

Mxp3: Ischium with small spine on flexor distal margin, extensor margin ending in acute point; crista dentata with 19 denticles. Merus as long as ischium; flexor margin with 2 subequal well-developed spines; extensor margin with distinct spine. Carpus unarmed.

P1: 3.1 times carapace length, with numerous finely setiferous scales, and some scattered long setae; setae non-iridescent. Merus 1.2 times length of carapace, 1.9 times as long as carpus, with spines arranged roughly in rows, dorsomesial spines stronger; distal spines prominent. Carpus 0.8–1.0 length of palm, twice longer than broad; dorsal surfaces with a few spines; mesial margin with some well-developed spines. Palm twice longer than broad, lateral and mesial margins subparallel; spines arranged roughly in dorsolateral and dorsomesial rows. Fingers unarmed, as long as palm, each finger with two rows of teeth distally spooned.

P2–4: Moderately long and slender, with setose striae and long setae; setae non-iridescent. P2 1.8 times carapace length. Meri successively shorter posteriorly (P3 merus 0.8 length of P2 merus, P4 merus 0.9 length of P3 merus); P2 merus 0.7 carapace length, 3.8 times as long as broad, 1.3 times longer than P2 propodus; P3 merus 2.8 times longer than broad, slightly longer than P3 propodus; P4 merus 2.7 times as long as broad, slightly longer than P4 propodus. Extensor margins of meri with row of 7 or 8 proximally diminishing spines on P2–3, 6 spines on P4; flexor margins distally ending in strong spine followed proximally by several tubercles or eminences; lateral sides unarmed. Carpi with 6 or 7 spines on extensor margin, distalmost smaller than distal second; lateral surface with 2 or 3 granules sub-paralleling extensor margin on P2–4; flexor margin blunty produced. Propodi 3.5–4.0 times as long as broad; extensor margin with 3 or 4 small proximal spines on P2–4; flexor margin with 5 or 6 slender movable spines on P2–4. Dactyli distally ending in well-curved strong spine, length 0.7–0.8 that of propodi; flexor margin with 5 proximally diminishing teeth, terminal one prominent.

Epipods only on P1.

Remarks. Galathea gnoma n. sp. is most closely related to G. denticulata Macpherson & Cleva. 2010 from Mayotte Island. The two species can be distinguished by the following characters:

- The rostral lateral tooth are shallowly incised in G. denticulata , but deeply incised in G. gnoma . - The carapace has one hepatic spine on each side but parahepatic spines are absent in G. denticulata , whereas the hepatic spines are absent but the parahepatic spines are present in G. gnoma .

The new species is also close to G. p a r v u l a (see under Remarks of this latter species).

No genetic data for G. gnoma are available.

Distribution. Indonesia (Kei Islands), Vanuatu; 20– 175 m.

Figures

FIGURE 43. Galathea gnoma n. sp., holotype, male, 2.7 mm, Indonesia, Kei Islands (MNHN-IU- 2013 - 13513). 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, E – H = 1 mm; B – D = 0.5 mm.