Galathea ploto Macpherson & Robainas-Barcia, 2015, n. sp.

Galathea ploto n. sp.

(Fig. 85)

Material examined. Holotype: New Caledonia. Lifou Island. LIFOU, Stn 1410, 20°56.7’S, 167°03.1’E, 2–4 m, 25 November 2000: M 3.4 mm (MNHN-IU-2013-9734).

Paratypes: New Caledonia. Lifou Island. LIFOU, Stn 1435, 20°55.2’S, 167°00.7’E, 5–30 m, 8 November 2000: 1 ov. F 3.0 mm (MNHN-IU-2013-13997).— Stn 1430, 20°47.5’S, 167°07.1’E, 20–25 m, 9 November 2000: 2 M 3.2–3.8 mm, 1 ov. F 2.6 mm (MNHN-IU-2013-15882).—Stn 1464, 20°54.5’S, 167°05.9’E, 35–50 m, 14 November 2000: 1 M 2.0 mm (MNHN-IU-2013-9718).—Stn 1449, 20°45.8’S, 167°01.65’E, 17 m, 17 November 2000: 1 ov. F 2.1 mm (MNHN-IU-2013-9715).—Stn 1451, 20°47.3’S, 167°06.8’E, 10–21 m, 19 November 2000: 1 ov. F 3.0 mm (MNHN-IU-2013-15879).—Stn 1410, 20°56.7’S, 167°03.1’E, 2–4 m, 25 November 2000: 1 ov. F 3.5 mm (MNHN-IU-2013-15880).— Stn 1455, 20°56.8’S, 167°02.7’E, 15–20 m, 25 November 2000: 1 M 3.1 mm, 2 ov. F 2.1–3.0 mm (MNHN-IU-2013-9716).—Stn 1421, 20°52.4’S, 167°08.5’E, 4 m, 27 November 2000: 1 ov. F 3.1 mm (MNHN-IU-2013-9719).—Stn 1457, 20°46.8’S, 167°02.75’E, 5–10 m, 27 November 2000: 7 M 2.6–3.5 mm, 3 ov. F 2.0– 2.6 mm, 2 F 2.0– 2.3 mm (MNHN-IU-2013-15881). Koumac Reef, 20 m, 6 October 1993: 1 M 2.9 mm, 1 ov. F 2.6 mm (MNHN-IU-2013-9717). Chesterfield Islands. CORAIL 2, Stn DW85, 19°12'S, 158°56'E, 32 m, 26 July 1988: 1 M 2.7 mm (MNHN-IU-2013-13928), 1 ov. F 3.0 mm (MNHN-IU-2013-13929), 1 ov. F 4.1 mm (MNHN-IU-2013-13930).

Etymology. The name Ploto, sailing, refers to one of the Nereids of Greek mythology. The name is considered as a substantive in apposition.

Description. Carapace: As long as broad; ridges with short fine setae, with a few scattered moderately long non-plumose setae; cervical groove slightly distinct, laterally bifurcated; gastric and anterior branchial regions only with interrupted ridges or scale-like ridges; 2 median epigastric spines; 1 hepatic spine on each side, near anterolateral spine; mid-transverse ridge uninterrupted, preceded by shallow cervical groove. Posterior branchial region with 4 ridges, 2 uninterrupted. Lateral margins convex medially, with 7 spines: 2 spines in front of, and 5 spines behind, anterior cervical groove; first anterolateral, well-developed, second small, accompanying another spine ventral to between first and second; 2 spines on anterior branchial margin, and 3 spines on posterior branchial margin. External orbital limit ending in small spine; infraorbital margin with 1 strong spine. Rostrum broad triangular, 1.3 times as long as broad, length 0.6 postorbital carapace length and breadth 0.4 that of carapace, nearly horizontal in lateral view; distance between distalmost lateral incisions 0.25 distance between proximalmost lateral incisions; dorsal surface with some short setae; lateral margin with 4 deeply incised sharp teeth.

Pterygostomian flap rugose, anterior margin acutely produced.

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

Abdomen: Somites 2–3 with 2 transverse ridges, anterior ridge more distinctly elevated than posterior ridge; somites 4–6 smooth, with minute scales, posteromedian lobe indistinct. Males with G1 and G2.

Eyes: Ocular peduncles 1.3 times longer than broad, maximum corneal diameter 0.7 rostrum width.

Antennule: Article 1 with 3 well-developed spines, distodorsal larger; distomesial spine slightly smaller than distoventral. Ultimate article with a few short fine setae, not in tuft, on distodorsal margin.

Antenna: Article 1 with ventral distomesial spine reaching end of article 2. Article 2 with 2 subequal distal spines, slightly exceeding midlength of article 3. Article 3 with distomesial spine; article 4 unarmed.

Mxp3: Ischium with well-developed distal spine on flexor margin, crista dentata with 19–21 denticles. Merus longer than ischium; flexor margin with 2 subequal spines; extensor margin unarmed. Carpus unarmed.

P1: 3.3 times carapace length, relatively slender. Merus 1.2 times length of carapace, 1.7 times as long as carpus, with spines arranged roughly in rows, 3 strong spines along mesial margin, distal spines prominent. Carpus 0.8 length of palm, 1.8 times as long as broad; dorsal surface with spines arranged roughly in longitudinal rows; mesial margin with 3 or 4 spines, distal second very strong. Palm 1.9–2.0 times longer than broad, lateral and mesial margins subparallel; spines arranged roughly in rows; dorsolateral row continuing on to lateral margin of fixed finger. Fingers 0.8 length of palm, each finger distally spooned, with two rows of fingers; movable finger with some proximal spines.

P2–4: moderately slender, with setose striae and sparse long non-plumose setae. P2 1.8 times carapace length. Meri successively shorter posteriorly (P3 merus 0.9 length of P3 merus, P4 merus 0.8 length of P3 merus); P2 merus 0.8 carapace length, 3.8 times as long as broad, 1.6 times longer than P2 propodus. Extensor margin with row of 7 or 8 proximally diminishing spines on P2–3, 4 spines on P4; ventral margins distally ending in strong spine followed proximally by 0–1 spines and several eminences, lateral unarmed. Carpi with 3 or 4 spines on extensor margin on P2–3; 0–1 spines on P4; lateral surface with 2 or 3 spines or acute granules sub-paralleling extensor margin; flexor distal margin acute. Propodi 4.3–4.8 times as long as broad; extensor margin with 3–5 proximal spines on P2–4; flexor margin with 4 slender movable spines. Dactyli distally ending in well-curved strong spine, length 0.6 that of propodi; flexor margin with 4 proximally diminishing teeth, terminal one prominent.

Epipods on P1.

Remarks. Galathea ploto n. sp. belongs to the group of species with scale-like ridges on the gastric region and without dorsal spines on the branchial regions. The closest relatives are G. bimaculata Miyake & Baba, 1966 from Japan to New Caledonia and Western Australia, G. bracteosa n. sp. from French Polynesia and G. p s i l a n. sp. from New Caledonia.

Galathea bracteosa is easily differentiated from the other two species by the presence of one facial pterygostomian spine, which is always absent in the other species.

Galathea ploto is easily differentiated from the other closely related species (G. bimaculata and G. p s i l a) by the presence of epigastric and hepatic spines on the carapace, whereas these spines are absent in the other species.

Galathea ploto is also close to G. magnifica Haswell, 1882 and G. schnabelae n. sp. (see Remarks of these species).

The genetic divergences among G. ploto, G. bimaculata, G. psila and G. bracteosa are larger than 15.0% (COI) and 6.1 % (16S rRNA) (Tab. 3).

Distribution. New Caledonia, Chesterfield Islands; 2– 50 m.