Metabetaeus Borradaile, 1899

Yamashita, Ryunosuke, Komai, Tomoyuki & Kon, Koetsu, 2023, Metabetaeus lapillicola, a new species of alpheid shrimp (Decapoda: Caridea) from Japan, inhabiting unusual pebble beaches, Zootaxa 5258 (3), pp. 317-330 : 328

Genus Metabetaeus Borradaile, 1899

Metabetaeus Borradaile, 1899: 1014 .— Holthuis 1993: 204.— Anker 2010: 38 .

Type species. Betaeus minutus Whitelegge, 1897 , by monotypy.

Composition. In addition to the type species, the following three species are now assigned to Metabetaeus : M. lohena Banner & Banner, 1960 , M. mcphersonae Anker, 2010 and M. lapillicola n. sp.

Emended diagnosis. Body moderately slender, not particularly compressed. Carapace smooth, glabrous, frontal margin with rostrum and orbital spines; posterior margin with deep cardiac notch. Pleomere 6 without articulated plate at posteroventral angle. Telson sub-rectangular, slightly tapering posteriorly; dorsal surface with 2 pairs of strong spiniform setae; posterior margin straight to rounded medially, each lateral angle with 2 pairs of strong spiniform setae; anal tubercles absent. Eyestalks completely concealed in dorsal and lateral views, but visible in anterior view; corneas more or less reduced, located in lateral position of eyestalk. Antennular peduncle with elongated and distally acute stylocerite; Lateral antennular flagellum with well-developed secondary ramus. Antennal peduncle with basicerite bearing strong ventrolateral distal spine. Scaphocerite with distinct distolateral spine and lamella. Mandible with two-segmented palp, with prominent dark-brown spot on incisor process. Maxilliped 3 pediform; lateral plate of coxa not acutely produced; ultimate article with small spiniform seta sub-distally. Pereopods 1 (= chelipeds) carried extended with dactylus in lateral position; carpus subcylindrical to vase-shaped, without comblike setal rows mesially; chela simple, smooth; linea impressa and adhesive discs absent; occlusal margins of fingers without snapping mechanism, unarmed or armed with simple teeth. Pereopod 2 with five-segmented carpus, first segment longest, third segment longer than second or fourth. Pereopods 3 and 4 slender; ischium usually with 1 or 2 spiniform seta(e) on lateral surface ventrally; merus usually with 1–3 spiniform seta(e) on lateral surface ventrally; propodus unarmed or armed with small spiniform setae ventrally; dactylus simple, acute distally, with minute setae subdistally. Male pleopod 2 with appendix masculina distinctly longer than appendix interna; female pleopod 2 with appendix interna only. Uropodal exopod with diaeresis bearing large subtriangular tooth adjacent to strong distolateral spiniform seta; endopod unarmed or with a tooth on distolateral margin.