Raripagurus, Lemaitre & Felder, 2023

Lemaitre, Rafael & Felder, Darryl L., 2023, A new genus and species of micro-pagurid hermit crab (Crustacea, Decapoda, Paguridae) from the rariphotic reef zone in Curaçao Lesser Antilles, Caribbean Sea, Zootaxa 5277 (2), pp. 374-380 : 375

Raripagurus n. gen.

Diagnosis. Eight pairs of biserial phyllobranch gills: 1 on maxillipeds 3, 1 on pereopods 1, 1 on pereopods 2, 2 on pereopods 3, and 3 on pereopods 4 (including 1 pleurobranch). Shield broader than long, glabrous; rostrum broadly triangular, distally rounded. Ocular acicles terminating in acute spine. Ischium of maxilliped 3 with accessory tooth. Chelipeds markedly unequal; carpus and propodus of right distinctly flattened dorsoventrally. Sternite of somite XII (thoracomere 6, pereopod 3) with ovate anterior lobe. Pereopod 4 semichelate, lacking propodal rasp; dactyl and propodus modified for grasping with small sharp spines distally, lacking preungual process. Pereopod 5 chelate, with few scales on rasp of dactyl and propodus. Male unknown. Female with paired gonopores; with paired first pleopods (gonopods) and unpaired left pleopod 2–5. Uropods and telson nearly symmetrical; telson lacking transverse sutures, terminal margin weakly subdivided into 2 broadly unarmed rounded lobes.

Species and distribution. Monotypic, with R. roseangelae n. gen., n. sp. known thus far from only Curaçao, Lesser Antilles, in the southeastern Caribbean.

Etymology. The generic name is derived from the genus name Pagurus , combined with the Latin prefix rarus, which denotes something scarce or rare, in reference to both the rareness of the morphology of the single species in this new genus and the rare, insufficiently explored rariphotic zone where this new species lives.

Remarks. The single species of this, for the time being monotypic genus, is distinct among the Paguridae in the flattened morphology of the right cheliped, grasping condition of the propodus and dactyl of pereopod 4, shape of telson, presence of paired first pleopods (gonopods) in the female, and having a reduced branchial formula of eight gills. Furthermore, the surfaces of carapace and thoracic appendages are unusually smooth, semi-transparent, unarmed, having only scattered setae. The flattened right cheliped and armature of the grasping spines on the propodus and dactyl of pereopod 4 is a unique condition among pagurids. However, other generic diagnostic characters are present in species of a few pagurid genera. In the single species of Raripagurus n. gen. the reduced gill formula with only eight pairs of gills is a character shared with species of Decaphyllus de Saint Laurent, 1968 , Paguriscus Lemaitre, Felder & Poupin, 2017 , Paguruncio Lemaitre, Felder & Poupin, 2017 , and Pusillopagurus Lemaitre, Felder & Poupin, 2017 . The shape of the telson of the single species of Raripagurus n. gen., lacking a transverse suture and having a posterior margin without spines or teeth and at most obscurely divided, is similar in species of Enallopaguropsis McLaughlin, 1981 . Finally, the presence in the single species of Raripagurus n. gen. of paired pleopods (gonopods) in females is a condition shared with all species of the 13 genera of the Pylopapagurus - Tomopagurus group ( Lemaitre & McLaughlin 2003). It would appear that none of these characters alone are indicative of close phylogenetic affinity.