Epicaridea Latreille, 1825

Williams, Jason D., Boyko, Christopher B. & Moritaki, Takeya, 2022, Two New Species of Spheroid Ectoparasitic Isopods (Epicaridea: Dajidae) Attached to the Antennules of Brachyuran Crab Hosts, with Description of a New Genus and Species of Hyperparasite (Epicaridea: Cryptoniscoidea), Species Diversity 27 (2), pp. 227-241 : 228

Infraorder Epicaridea Latreille, 1825 Superfamily Cryptoniscoidea Kossmann, 1880 Family Dajidae G. O. Sars, 1883 Genus Akrophryxus Williams and Boyko, 2021

Type species. Akrophryxus milvus Williams and Boyko, 2021 , fixed by original designation.

Diagnosis. Female: body spheroid; cephalon externally indistinguishable from pereon. Antennules absent, antennae each as oblong flat plate lateral to oral cone. Maxillipeds ovate with recurved digitiform extension. Pereopods 1–5 subequal in size and shape. Oostegite 1 largest, broadly ovate with small posterior accessory lobe; oostegites 2, 3, 4 progressively larger; oostegite 5 present or absent. Pleon modified as oblong, narrow, thickened plate with two or three circular medial holes, largest surrounding antennule of host. Male: cephalon fused with pereomere 1; cephalic slits present. Antennules reduced, flagella absent; antennae of one or two broad elongate lobes lateral to oral cone, flagella absent. Pereomeres 2–6 distinct; pereomere 7 fused with pleon, lateral margins recurved ventrally. Pereopods 1–6 subequal in size; pereopod 7 lacking. Pleon rounded, all segments fused and fused with pereomere 7; pleopods lacking. Cryptoniscus larva: body tear-drop shaped. Cephalon anterior margin round, posterolateral margins extending posteriorly; eyes unpigmented. Antennules of three articles each, without teeth. Antennae of nine articles each. Pereomeres 1–7 with smooth coxal plates, each pereomere notched medially. Pereopods 1 and 2 subequal, dactyli short, slightly curved, propodus inner margin folded, bearing two flat, multifid setae; carpus with single distal multifid seta. Pereopods 3–5 dactyli more elongate, curved, propodi more elongate, narrower, inner margin of each folded, bearing two flat, multifid setae; carpi each with single distal multifid seta. Pereopod 6 dactylus subequal in length to those of pereopods 3–5, propodus more elongate and narrower than those of pereopods 3–5, inner margin slightly folded, bearing two stout, multifid setae, carpus with single distal multifid seta. Pereopod 7 similar to pereopod 6 but with elongate dactylus extending to distal margin of merus, carpus with single flattened multifid seta.

Remarks. The below description of the cryptoniscus larval stage is the first for this genus. The cryptoniscus is similar to that described for the closely related T. clypeus ; the principal differences being that the cryptoniscus of A. acinaces sp. nov. has a notch on the lateral margin of each pereomere (lacking in T. clypeus ), the antennule segments are flatter and smoother (thicker and more sculptured in T. clypeus ), and the dactyl of pereopod 7 is proportionally much longer, the propodus thinner, and the multifid spines on the propodus and carpus are much smaller than those of T. clypeus ( Williams and Boyko 2021) .

The three species of Akrophryxus are not only different in several morphological characters of females and males but were found parasitizing hosts belonging to three different heterotreme brachyuran families: Ethusidae , Goneplacidae , and Palicidae from Madagascar (821–910 m), Japan (200 m), South China Sea (410–412 m), respectively ( Williams and Boyko 2021).