Xenuraega Tattersall, 1909

Shimomura, Michitaka & Bruce, Niel L., 2019, A new species of the mesopelagic isopod genus Xenuraega Tattersall, 1909 (Crustacea: Isopoda: Aegidae) from Japan, the second species in the genus, Zootaxa 4683 (3), pp. 431-438 : 432

Genus Xenuraega Tattersall, 1909

Xenuraega Tattersall, 1909: 215 ; 1911: 198.— Bruce, 1993: 618.

Type species: Xenuraega ptilocera Tattersall, 1909 ; by monotypy ( Bruce 1993).

Diagnosis (diagnostic characters in bold). Body narrow, elongate, about 3.3–4.3 times as long as wide. Cephalon anterior margin forming median point. Coxae present, all shorter than respective pereonite, not posteriorly produced. Pleon about 30–45% total BL, pleonites 1–5 all visible, with free lateral margins, epimera not posteriorly produced. Pleotelson relatively small, not containing or concealing pleopods.

Antennula peduncle 3-articled. Antenna peduncle articles 4 and 5 without long plumose setae, flagellum extending to or beyond pleotelson.

Frontal lamina absent, clypeus and narrow labrum present. Mandibular incisor unicuspid or absent. Maxillula slender, styliform with four or five terminal spines; mesial lobe absent. Maxilla with two terminal robust setae, mesial lobe fused to lateral lobe or absent. Maxilliped with three articles; article 3 folded across axis of article 2, with one small and two large terminal recurved robust setae.

Pereopods 1–3 robust, dactylus subequal in length to propodus, propodal palm not expanded or plate-like; pereopods 4–7 elongate; dactylus shorter than propodus; all dactyli strongly curved.

Pleopods 1–5 with both rami elongate; pleopods 1–5 peduncles with coupling hooks; pleopods 3–5 endopods without PMS; pleopod rami extending laterally and posteriorly beyond pleon and pleotelson. Uropod peduncle lacking mesial lobe; one or both rami elongate (22–80% BL). Mature sexual characters not observed.

Remarks. Xenuraega Tattersall, 1909 differs from all other genera in lacking a frontal lamina, the maxillula lacking a mesial lobe and the pleonites are laterally free without any posterior extension or point (see Bruce 2009 for comparison to other genera). In addition, the uropod peduncle lacks a mesial lobe and one or both rami may be greatly elongate, from 22–80% total body length, and in the case of Xenuraega bythionekta sp. nov., which has the shorter uropods, the rami as still seven times as long as proximal width. The most similar genus is Syscenus Harger, 1880 (see Bruce 2005, 2009) and Xenuraega can be distinguished from that genus by exceptionally elongate uropodal rami that are provided with numerous long plumose setae. The relationships of Xenuraega with the Aegidae were discussed by Bruce (1993) and are not repeated here.