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

Galathea rhanis sp. nov.

( Fig. 10 View FIGURE 10 )

Material examined. Holotype: Papua-New Guinea, PAPUA NIUGINI, Stn PB 19, 05°05.1’S, 145°48.6’E, 30 December 2012, 10 m: ov. F 2.4 mm (MNHN-IU-2014-13935). GoogleMaps

Paratype: same data than holotype: 1 M 2.2 mm (MNHN-IU-2014-20839).

Etymology. From the Greek, rhanis , drop, spot, in reference to the small size of the species.

Description. Carapace: As long as broad; anterior cervical groove indistinct. Five ridges on gastric region: 1 epigastric ridge, medially convex and interrupted, with 2 epigastric spines; 1 protogastric ridge uninterrupted, without parahepatic spines; 1 mesogastric ridge extending laterally to anteriormost of branchial marginal spines, uninterrupted or with minute interruption medially; 2 metagastric ridges, anterior ridge medially interrupted and extending laterally to branchial margin, posterior ridge short. Mid-transverse ridge uninterrupted, preceded by shallow cervical groove, followed by 5 ridges, 1–2 uninterrupted ridges. Lateral margins medially convex, with 6 spines: 1 spines in front of and 5 spines behind indistinct anterior cervical groove; first anterolateral, well-developed, at same level of lateral limit of orbit; 2 spines on anterior branchial region, last small, and 3 spines on posterior branchial margin, last small. External orbital limit ending in small spine; infra-orbital margin with strong spine. Rostrum broad triangular, 1.1–1.2 times as long as broad, length 0.5 postorbital carapace length and breadth 0.4 that of carapace, nearly horizontal in lateral view; distance between distalmost lateral incisions 0.3 distance between proximalmost lateral incisions; dorsal surface with some short setae; lateral margin with 4 deeply incised sharp teeth.

Pterygostomian flap rugose, with facial small spine on anterior part, anterior margin ending in small spine.

Thoracic sternum: As long as broad, lateral extremities gently divergent posteriorly. Sternite III with median shallow notch, anterior margin at each side of notch slightly convex. Sternite IV with anterior part as wide as sternite III, with some minute striae. Sternites IV–VI with a few striae on lateral sides. Sternite III ~ 1.8 × as wide as long; sternite IV nearly 3 × as wide as long, and 2.5 × as wide as sternite III.

Pleon: Tergite II with 2 transverse ridges on tergite, anterior ridge more distinctly elevated than posterior ridge; tergites III and IV smooth or with some scales, with anterior ridge only; tergite of somites V and VI smooth. Males with G1 and G2.

Eye: Ocular peduncles 1.2 times longer than broad, maximum corneal diameter 0.6 rostrum width.

Antennule.Article 1 with 3 well-developed distal spines, distodorsal larger; distomesial spine reaching midlength of distolateral spine. Ultimate article with a few short setae not in tuft on distodorsal margin.

Antenna. Article 1 with distomesial process reaching distal margin of article 2. Article 2 with distomesial spine barely shorter than distolateral spine, exceeding midlength of article 3. Articles 3 and 4 unarmed.

Mxp3. Ischium with well-developed distal spine on flexor margin; extensor margin unarmed; crista dentata with 26–27 denticles. Merus subequal in length to ischium, with 2–3 small spines on flexor margin, proximal one located at midlength, distal one at terminal end, median spine slightly smaller than others or obsolescent; extensor margin with distal spine.

P1. Lost in both specimens.

P2–4. Relatively slender, somewhat compressed, moderately setose. P2 1.5 times carapace length. Meri successively shorter posteriorly (P3 merus 0.9 length of P2 merus, P4 merus 0.8 length of P3 merus); P2 merus 0.6 carapace length, 3 times as long as broad, 1.3 times longer than P2 propodus; P3 merus 3.0 times as long as broad, 1.3 times length of P3 propodus; P4 merus 2.5 times as long as broad, 1.1 length of P4 propodus. Extensor margins with row of 6 proximally diminishing spines on P2–3, 4 spines on P4; lateral surface unarmed on P2–3, 0–1 spines on P4; flexolateral margin with strong terminal spine. Carpi with 3–4 spines on extensor margin; lateral surface with row of 2–4 small spines or acute granules paralleling extensor row; flexor distal margins with spine. Propodi 4 times as long as broad; extensor margin with 0–2 proximal spines on P2–4; flexor margin with 3–4 slender movable spines. Dactyli subequal in length, 0.7 length of propodi, ending in incurved, strong, sharp spine; flexor margin with prominent triangular terminal tooth preceded by obsolescent 4–5 teeth.

Epipods present on P1–3.

Setae: Three types of setae were observed, (1) short plumose setae, with setules along both sides of shaft, densely located on ridges of carapace and pleon; (2) long thick iridescent simple setae, sparsely located on pleon and P2–4; (3) short thick iridescent simple setae, sparsely located on pleon and P2–4.

Genetic data. COI.

Remarks. Galathea rhanis sp. nov. belongs to the group of species having an uninterrupted mesogastric ridge between the anteriormost branchial marginal spines, one pair of epigastric spines, the pterygostomian flap with 1 facial spine on the anterior part, epipods on P1–3 and the antennal article 3 with distal spines. The new species is closely related to G. paulayi Macpherson & Robainas-Barcia, 2015 from the French Polynesia and Kiribati and G. stilla sp. nov. (see below).

The new species is easily distinguished from both species by the following characters:

—The parahepatic spines are absent in G. rhanis , whereas these spines are present in the other two species.

—The carapace lateral margin without a spine between the anterolateral spine and the anteriormost spine of the branchial margin in G. rhanis , whereas this spine is always present in G. paulayi and G. stilla .

—The genetic divergences with G. paulayi and G. stilla are 17.63% and 18.57% for COI, respectively.

Distribution. Papua New Guinea, at 10 m.