Galathea bicornis, Macpherson & Rodríguez-Flores & Machordom, 2025

Galathea bicornis sp. nov.

( Figs. 3C View FIGURE 3 , 6 View FIGURE 6 )

Material examined. Holotype: New Caledonia. KOUMAC, Stn KL 37, 20°49.9’S, 164°16.7’E, 81 m, 17 September 2018: M 2.5 mm (MNHN-IU-2014-20126). GoogleMaps

Etymology. From the Latin cornis, thorny, and bi, two, in reference to the pair of protogastric and cardiac spines on the carapace dorsal surface

Description. Carapace: As long as broad; anterior and posterior cervical grooves distinct; dorsal surface with scale-like and interrupted ridges in all regions; mid-transverse ridge laterally interrupted and not scale-like, preceded by distinct cervical groove; transverse groove before cardiac spines; ridges not densely setose, with short simple setae (sometimes with a few short setules) and with some long and median thick plumose setae on protogastric and cardiac ridges. Epigastric region with 4 small spines; 2 submedian protogastric spines, and 2 parahepatic spines on each side; 2 postcervical spines on each side of mid-transverse ridge, 1 branchial spine on each side, behind mid-transverse ridge and 2 median cardiac spines. Lateral margins slightly convex, with 7 spines: 2 spines in front of and 5 strong spines behind anterior cervical groove; first anterolateral, well-developed, distinctly posterior to level of lateral limit of orbit; second small, situated at midlength between anterolateral spine and anterior cervical groove, accompanying another small spine ventral to between first and second; 2 spines on anterior branchial region, and 3 spines on posterior branchial margin. Outer orbital angle acute; infra-orbital margin with 1 or 2 spines. Rostrum 1.8 times as long as broad, length 0.6 that of, breadth 0.3 that of carapace; distance between distalmost lateral incisions 0.3 distance between proximalmost lateral incisions; dorsal surface nearly horizontal in lateral view, with minute setiferous ridges; lateral margin with 4 sharp teeth.

Pterygostomian flap rugose with sparse setae, anteriorly rounded; some granules on upper margin near linea anomurica.

Thoracic sternum: 1.2 × as long as wide. Sternite III with median shallow notch. Sternite IV as wide as following sternites, with anterior part as wide than sternite III, with some short striae. Sternites IV–VI with a few striae. Sternite III ~ 2.1 × as wide as long; sternite IV nearly 2.1 × as wide as long, and 3.2 × as wide as sternite III.

Pleon: Tergites II and III each with 2 transverse uninterrupted ridges on tergite, anterior ridge more distinctly elevated than posterior ridge; tergite of somites IV and V with short median ridge; somite VI with 2 scale-like ridges, posteromedian margin straight. Males with G1 and G2.

Eye: Ocular peduncles 1.8 times longer than broad, maximum corneal diameter 0.8 rostrum width.

Antennule: Article 1 with 3 distal spines, 2 well-developed spines, distodorsal larger than others; distomesial spine small but distinct; additional small spine on lateral margin. Ultimate article with a few short setae not in tuft on distodorsal margin.

Antenna: Article 1 with depressed ventral distomesial process clearly not reaching distal margin of article 2. Article 2 with small distomesial and distolateral spines, not reaching midlength of article 3. Article 3 with small distomesial spine. Article 4 unarmed.

Mxp3: Ischium with spine on extensor and flexor distal margins; crista dentata with 20–21 denticles. Merus subequal in length to ischium, with 3 subequal spines on flexor margin; extensor margin with small distal spine. Carpus with several spines along extensor margin.

P1: Lost.

P2 and 4: Relatively short, somewhat compressed, sparsely setose with some simple setae and some scattered thick long plumose setae on all articles. Meri successively shorter posteriorly (P4 merus 0.7 length of P2 merus), equally broad; P2 merus 0.8 carapace length, 4.0 times as long as broad, 1.3 times longer than P2 propodus; P4 merus 2.7 times as long as broad, as long as P4 propodus. Extensor margins of P2 merus with row of 6 proximally diminishing spines, 2–3 spines on P4; lateral surface with 0–2 small spines; ventrolateral margins ending in strong terminal spine proximally followed by smaller spine; flexomesial margin with 4 spines on P2, unarmed on P4. Carpi each with 3–4 spines on extensor margin on P2 and P4; lateral surface with row of 2–4 small spines or acute granules paralleling extensor row; flexor distal margins with very small distal spine. Propodi 4.5 times as long as broad; extensor margin with 2–3 proximal spines on P2, unarmed on P4; flexor margin with 5–6 movable spines. Dactyli subequal in length, 0.7 length of propodi, ending in incurved, strong, sharp spine; flexor margin with 5–6 successively diminishing teeth, terminal tooth prominent.

Epipods present on P1, absent on P2–3.

Setae: Two types of setae were observed, (1) moderately short simple setae, not dense, sometimes with a few minute setules along both sides of first half of shaft, located on ridges of carapace and pleon, and scales of P1–4; (2) long thick plumose setae, with setules along one side of shaft, distally forming a tuft ( Fig. 3C View FIGURE 3 ), sparsely located on carapace, around protogastric and cardiac spines, pleon, and P2–4. Considering the small size of the unique specimen, with both P1 lost, the type of setae should be considered as provisional.

Genetic data. COI and 16S.

Remarks. The new species belongs to the group of species having the carapace with median protogastric and cardiac spines and the antennular article 1 with minute distomesial spine. This group contains G. sentosa Macpherson & Robainas-Barcia, 2015 from Wallis and Futuna area and G. robusta Baba, 1990 from Madagascar and La Reunion from which it can be distinguished by the following characters:

— G. robusta has the metagastric region armed with 2 median spines, whereas this region is unarmed in G. bicornis . Furthermore, each anterior branchial region has 1 spine in G. robusta , whereas this spine is absent in the new species.

— G. sentosa has the cardiac region with a transverse row of 4–6 spines, whereas there are only 2 median spines in the new species. Furthermore, the new species has 1 dorso-branchial spine on each side, behind the mid-transverse ridge, whereas this spine is absent in G. sentosa .

Genetically, G. bicornis shows divergences in COI of 11.12% from G. robusta , and 10.54% from G. sentosa . The new species is also relatively close to G. pascualae Macpherson & Robainas-Barcia, 2015 , from New Caledonia and Vanuatu (10.91%). However, both species are easily differentiated by the absence of median spines on the metagastric and cardiac regions in G. pascualae . There is no 16S data available for G. sentosa , but G. bicornis sp. nov. shows genetic divergence of 3.93 % from G. pascualae and 14.02% from G. robusta .

Distribution. New Caledonia, 81 m.