Ryukyua Williams & Bunkley-Williams, 1994

Vigneshwaran, P., Ravichandran, S. & Martin, Melissa B., 2018, Redescription of Ryukyua circularis (Pillai, 1954) (Isopoda, Cymothoidae), parasite of the Bleeker smoothbelly sardinella Amblygaster clupeoides Bleeker, 1849 from India, Zootaxa 4526 (2), pp. 195-206 : 196

Genus Ryukyua Williams & Bunkley-Williams, 1994

Ryukyua Williams & Bunkley-Williams, 1994: 155 –161.

Livoneca — Pillai, 1954: 17; 1964: 218–220 [partim].

Type species: Ryukyua globosa Williams & Bunkley-Williams, 1994 , by original designation ( Williams & Bunkley-Williams 1994).

Diagnosis: Generic diagnosis of Ryukyua is here adapted from Williams & Bunkley-Williams (1994).

Female: Body round, almost spherical in gravid females, compact, widest at pereonites 4 and 5; pereonite 7 shortest, pereonite 6 0.5 as long times as long as pereonite 5. Cephalon immersed in pereonite 1, anterior margin rounded to form blunt rostrum. Eyes 0.3 times cephalon width. Pleonites visible in dorsal view, lateral margin of pereonite 7 produced posteriorly and overlapping lateral margin of pleonites 1–4; pleon narrower than pereon. Pleotelson wider than long, posterior margin straight to broadly rounded or slightly emarginated. Antennula and antennae with 8–9 articles, antennula shorter than antennae in length and well-separated. Mandible palp article 3 shorter than article 2. Maxilliped palp article 2 without setae, proximal part of maxilliped not expanded. Maxilla medial lobe partially fused to lateral lobe. Pereopods stout, propodus as wide as long; pereopods 1–4 short, 5–6 longer. Pleopods without folds, pockets, setose or protrusions; uropods not reaching posterior margin of pleotelson, rami elongate-oval, subequal in length.

Remarks: Williams & Bunkley-Williams (1994) provided a brief diagnosis for the genus Ryukyua . Ryukyua can be identified by the strongly compact and spherical body; mandibular palp all articles distinct article 3 shorter than article 2; coxae partially visible dorsally, shorter than respective pereonites; uropod rami elongate-oval, subequal in length.

Other branchial cymothoids differ with Ryukyua in the following: Cterissa Schiöedte and Meinert, 1884 : body dorsoventrally flattened, laterally expanded and more flattened on one side, coxae 2–7 visible, with posteroventral angles expanded at one end rounded; body round, almost spherical, pleonites 1–3 lateral margins not bilobed ( Bunkley-Williams & Williams 1986); Agarna Schiödte and Meinert, 1884 : pereon elevated mid-dorsally, pereonites 3–7 are greatly expanded laterally; pereonite 7 posteriorlaterally produced and overlapping pleonites 3– 5 ( Williams & Bunkley-Williams 1994; Aneesh et al. 2018); Joryma Bowman & Tareen, 1983 : pereonite width to pleotelson width ratio similar (vs wider pereon to pleotelson ratio), mandible simple with less pronounced incisor (vs incisors acute), mandible palp with weak segmentation, pereopod 7 dactylus slender and reaching beyond carpus, pereopod 7 ischium stout and expanded (vs slender, without expansion) ( Bowman & Tareen 1983); Elthusa: Schiöedte and Meinert, 1884 : coxae 4–7 from dorsal view, eyes width 1/3 cephalon width (vs 2/3 cephalon width), maxilliped article 3 slender and with setae ( Bruce 1990; Hadfield et al. 2017); Norileca Bruce, 1990 : pleopod 5 with folds, pleopods 2–5 peduncle with laminar lobe, body strongly twisted to one side, mandible palp article 2 greatly expanded, brood pouch with posterior pocket, pleonites 1 and 2 without ventro-lateral processes ( Bruce 1990); Mothocya Costa in Hope, 1851 : cephalon with rostrum, pleon partly overlapped by pereonite 7, pleotelson posterior region rounded, with appendix masculine on pleopod 2 ( Bruce 1986); Livoneca Leach, 1818 : coxae longer than respective pereonite; pleon not immersed in pereon, pleonites becoming progressively narrow towards posterior; ventrolateral margin of pleonites 1–3 weakly bilobed ( Bruce 1990).