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

Galathea hydrae n. sp.

(Fig. 48)

Galathea dispersa. — Barnard, 1950: 486, figs 91f–h (False Bay and Agulhas Bank to Natal and Zululand, 24–113 m).— Kensley, 1981a: 34 (list).— Tirmizi & Javed, 1993: 67, fig. 29 (western Indian Ocean between S. Mozambique and South Africa (24–29°S), 69–165 m) (not G. dispersa Spence Bate, 1859).

Material examined. Holotype: Mozambique. MAINBAZA, Stn CC3159, 23°53.80’S, 35°37.58’E, 148–152 m, 15 Abril 2009: F 3.5 mm (MNHN-IU-2013-8308).

Paratypes: Mozambique. MAINBAZA, Stn CP3132, 25°11.24’S, 35°01.51’E, 101–102 m, 10 Abril 2009: 1 M 4.1 mm (MNHN-IU 2008-10230).—Stn CC3159, 23°53.80’S, 35°37.58’E, 148–152 m, 15 Abril 2009: 2 F 2.0–3.0 mm (MNHN-IU-2013-8309).

Etymology. The name Hydra, the Sea Serpent, refers to one of the southern hemisphere constellations.

Description. Carapace: slightly longer than broad; transverse ridges with dense short setae, and some scattered long non-plumose setae; cervical groove distinct, laterally bifurcated. Gastric region with some transverse ridges: 1 epigastric ridge medially interrupted, with 3 pairs of epigastric spines; 2 protogastric ridges, anterior ridge between second lateral spines, laterally interrupted, convex medially and with 1 parahepatic spine on each side, posterior ridge scale-like, median scale convex, with some long non-plumose setae; some scales between epigastric and anterior protogastric ridges; 2 mesogastric ridges, anterior ridge uninterrupted but not extending laterally to anteriormost of branchial marginal spines, posterior ridge scale-like; 2 metagastric ridges, uninterrupted, with some scales between them, and not continuing laterally with anterior branchial region. One-two small hepatic spines near first marginal spine (anterolateral). 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 well convex medially, with 8 spines: 2 spines in front of and 6 spines behind anterior cervical groove; first anterolateral, well-developed, at same level of lateral limit of orbit; second, small, at midlength between anterolateral spine and anteriormost spine of branchial margin, with spine ventral to between first and second; 3 spines on anterior branchial region, last small, and 3 spines on posterior branchial margin, last small. Small frontal spine between lateral limit of orbit and anterolateral spine; infraorbital margin with 4 or 5 minute spines. Rostrum 1.6 as long as broad, length 0.6 postorbital carapace length and breadth 0.4 that of carapace; distance between distalmost lateral incisions 0.3 distance between proximalmost lateral incisions; dorsal surface nearly horizontal in lateral view, with numerous setae; lateral margin with 4 deeply incised sharp teeth.

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

Sternum: 0.9 times as long as broad, lateral extremities gently divergent posteriorly.

Abdomen: Somites 2–3 each with 2 uninterrupted transverse ridges on tergite; somite 4 with 2 ridges, posterior ridge medially interrupted; somites 5 and 6 each with 2 medially interrupted ridges, posteromedian margin of somite 6 slightly convex. Males with G1 and G2.

Eyes: Ocular peduncles 1.3 times longer than broad, maximum corneal diameter 0.6 rostrum width.

Antennule: Article 1 with 3 well-developed distal spines, distodorsal larger. 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 2 welldeveloped distal spines, distolateral spine slightly larger than distomesial and nearly reaching end of article 3. Article 3 with distomesial spine. Article 4 unarmed.

Mxp3: Ischium with well-developed spine on flexor distal margin; extensor margin with small distal spine; crista dentata with 23–24 denticles. Merus as long as ischium; flexor margin with 2 or 3 spines, proximal clearly stronger than other spines; extensor margin with small distal spine. Carpus unarmed.

P1: 2.5 times carapace length, covered with finely setiferous scales, with scattered long setae. Merus as long as carapace, 3.5 times as long as carpus, with spines arranged roughly in rows, dorsomesial spines stronger; distal spines prominent. Carpus 0.5 length of palm, twice longer than broad; dorsal and lateral surfaces with some spines; mesial margin with 3 or 4 spines (distal second strong). Palm 1.8 times longer than broad, lateral and mesial margins slightly convex; spines arranged roughly in dorsolateral and dorsomesial rows, some small spines scattered on dorsal side; dorsolateral row continuing along entire fixed finger. Fingers as long as palm, each finger distally with two rows of teeth, spooned; mesial margin of movable finger with proximal spines.

P2–4: moderately slender, with setose striae and sparse long plumose setae. P2 1.8 times carapace length. Meri successively shorter posteriorly (P3 merus 0.9 length of P2 merus, P4 missing); P2 merus 0.7 carapace length, 4.8 times as long as broad, 1.5 times longer than P2 propodus; P3 merus 3.8 times longer than broad, 1.4 times longer than P3 propodus; distoflexor angle of P2–4 with 2 spines. Extensor margin of P2–3 meri with row of 7–9 proximally diminishing spines; ventral margins distally ending in strong spine followed proximally by 0–1 spines and several eminences; lateral sides unarmed on P2–3. Carpi with 5 spines on extensor margin on P2–3; lateral surface with 2 or 3 small spines sub-paralleling extensor margin on P2–3; flexor distal margin with spine. P2–3 propodi 4.7–5.1 times as long as broad; extensor margin unarmed; flexor margin with 4 or 5 slender movable spines. P2 dactylus (P3–4 dactyli missing) distally ending in well-curved strong spine, length 0.7 that of propodus; flexor margin with 4 proximally diminishing teeth, terminal one prominent.Epipods present on P1–3.

Remarks. The new species is easily differentiated from the other closely related species, G. pascualae n. sp. from Indonesia, Vanuatu, New Caledonia, Loyalty and Chesterfield Islands and G. pubipes n. sp. from New Caledonia, by the following features:

- The epipods are present on P 1–3 in G. hydrae, whereas they are present only on P 1 in the latter two species.

- The distal angle of the flexor margin of the P2–4 meri has two spines in G. hydrae, instead of one spine only in the other species.

The genetic divergences with these species are always higher than 13.4% (16S rRNA) (Tab. 2).

The new species is also close to G. brevimana Paul’son, 1875 and G. micra n. sp. (see respective Remarks of these species).

This new species was previously identified with G. dispersa Bate, 1859, by Barnard (1950) and Tirmizi & Javed (1993). Galathea dispersa is a common species distributed from the north-east Atlantic and the Mediterranean Sea, and it can be distinguished from G. hydrae by the number of transverse ridges on the carapace and abdomen, more numerous en G. dispersa than in G. hydrae. Furthermore, G. hydrae has one parahepatic spine on each side, which is absent in G. dispersa.

Distribution. Mozambique, 101– 152 m.