Ryukyua circularis
Creators: name: Ravichandran, S.
name: Vigneshwaran, P.
name: Rameshkumar, G.
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Cymothoidae
Ryukyua
Ryukyua circularis

description: Ryukyua circularis (Pillai, 1954)
(Fig. 13 m–o)
Livoneca circularis Pillai, 1954: 17; 1964: 218–220, figs 4l, 5, 7f.
Lironeca circularis Williams & Williams, 1986: 213–215, fig. 1a–e.
Ryukyua circularis. — Williams & Bunkley-Williams, 1994: 160, figs 28–32.— Trilles, Ravichandran & Rameshkumar 2011: 453.— Rameshkumar, Ravichandran & Allayie, 2013b: 127–132.— Aneesh, Helna & Sudha, 2016: 1270–1277, fig. 1m, n.—Praveenraj, Saravanan, Puneeth Kumar, Ravichandran,Arunjyoti Baruah, Monalisha Devi, Kiruba Sankar & Dam Roy, 2017: 593–595, fig. 1.— Vigneshwaran, Ravichandran & Martin, 2018d: 200–205, figs 1–6.
Type and type locality. The type, Pillai’s Indian specimens of Livoneca circularis are not extant. The type locality is Trivandrum, India.
Material examined. 5 ovig. females, (9–13 mm), Mandapam, 18 May 2017, from Amblygaster clupeoides, coll. P. Vigneshwaran (CAS / MBRM C- 222– C- 226); 2 non ovig. females (9, 12 mm), (CAS / MBRM C-227 – C-228); 2 males (7, 8 mm), (CAS / MBRM C-229 – C-230).
Remarks. Ryukyua circularis can be recognized by its oval to rounded body shape, widest at pereonites 3–5, cephalon deeply immersed in pereonite 1. The pleotelson of R. circularis is anterior lateral margins weakly convex, posterior margin roughly triangular and the uropods half the length of pleotelson, rami not extending beyond the pleotelson. Furthermore, pleonites 1–3 partially overlapped by a posterolateral margin of pereonite 7. More recently the Indian specimen of R. circularis was redescribed by Vigneshwaran et al. (2018d).
Ryukyua circularis attaches to the ventral part of the host branchial cavity, with the cephalon to the anterior end of the host, and with its dorsal side (pereon and pleon) directed outwards, facing the branchial cavity. Its rounded and slightly asymmetrical body thus it occupies both branchial cavity of host fish (Rameshkumar et al. 2013; Aneesh et al. 2016).
Ryukyua circularis and R. globosa have a near identical morphology of cephalon deeply immersed in pereonite 1; body widest at pereonites 3–6; pereopods with rather a broad basis, elongate ischium and short propodus; and all pleopods are laminar. The host distribution of both species of Ryukyua similar. R. globosa can be distinguished from R. circularis by being broad and rounded body shape, the posterolateral margin of pereonite 7 produced and overlap all pleonites, pleotelson a little wider than long and having a rectangular instead of a triangular shape.
Colour. Both female and male appear white to yellowish-tan in alcohol; manca appear mahogany brown, with chromatophores scattered posteriorly on the pereon and pleotelson (Vigneshwaran et al. 2018d).
Size. Ovig. females 9–13 mm; non ovig. females 9–12 mm; males 6–8 mm (Vigneshwaran et al. 2018d).
Distribution. The species R. circularis has been known to distribute in widely. For locality details see Vigneshwaran et al. (2018d).
Host. Known only from family Clupeidae. For fish host species details, see Vigneshwaran et al. (2018d).
description: Published as part of Ravichandran, S., Vigneshwaran, P. & Rameshkumar, G., 2019, A taxonomic review of the fish parasitic isopod family Cymothoidae Leach, 1818 (Crustacea: Isopoda: Cymothooidea) of India, pp. 1-99 in Zootaxa 4622 (1) on pages 73-74, DOI: 10.11646/zootaxa.4622.1.1, http://zenodo.org/record/3379899