Ryukyua globosa Williams & Bunkley-Williams, 1994

Ravichandran, S., Vigneshwaran, P. & Rameshkumar, G., 2019, A taxonomic review of the fish parasitic isopod family Cymothoidae Leach, 1818 (Crustacea: Isopoda: Cymothooidea) of India, Zootaxa 4622 (1), pp. 1-99 : 74-78

Ryukyua globosa Williams & Bunkley-Williams, 1994

( Figs 13 p–r, 20–22)

Ryukyua globosa Williams & Bunkley-Williams, 1994: 156–160 , figs 1–27.—Rameshkumar Ramesh & Ravichandran, 2014a: 1293–1295, figs 1, 2.

Type and type locality. Holotype ( USNM 231038 ), associated male paratype ( USNM 231042 ), from Amblygaster sirm , hoshi-yamato-mizum, northern Okinawa, Toguchi Market , Motobu-cho, Okinawa, Japan, 14 September 1985.

Material examined. 4 ovig. females (14–18 mm), Mandapam , 18 January 2016, from Sardinella gibbosa , coll. P. Vigneshwaran (CAS/MBRM C-234 – C-238 ) , 1 ovig. female (14 mm), Parangipettai , 14 April 2017, from Sardinella gibbosa , coll. S. Ravichandran ( ZSI / MBRC D1-552 ), the Southeastern coast of India .

Description female. Body oval, almost spherical, 2.3 times as long as wide, weakly twisted; widest at pereonites 4 and 5. Anterior margin of cephalon ventrally flexed, posterior margin of cephalon deeply immersed in pereonite 1. Eyes moderate, partly covered by pereonite 1 and visible dorsally. Pereonite 1 with posterolateral angles weakly produced, posterolateral angles of pereonites 2–4 produced posteriorly and those of pereonites 2 and 3. Pereonites 1 and 7 shortest, 3, 4 and 5 longest 2 and 6 subequal in length; posterior margin of pereonite 7 concave. Coxae of pereonites 2–4 laterally produced in enlarged and inflated, coxae 5–7 each shorter than respective segments not visual in dorsally. All pleonites dorsally visible, pleonites 1–4 laterally overlapped by pereonite 7. Pleotelson 2.8 times wider than long, rectangular, posterior border straight to broadly rounded or slightly emarginated.

Antennula composed with 8 articles, articles 2 and 3 longer than others, articles 4–8 with simple setae. Antenn with 8 or 9 articles, articles 4 and 5 longer than others, articles 5–8 with simple setae, not reaching posterior morgin of cephalon. Mandible with large palp, articles 2 and 3 slightly in flattened. Maxilla with 2 recurved spines on each lobe. Maxillula with 2 stout and 2 slender slightly recurved apical spines. Maxilliped article 3 with 3 recurved apical spines.

Pereopods stout, propodus as wide as long, merus of pereopods 6 and 7 expanded, Pereopods 2 and 3 longer than pereopod 1. Pereopods 4–7 basis with posterior expansion becoming progressively larger toward posterior. Pereopods 5–7 carpus short, triangular. Pleopods all lamellar, all peduncles with developed lobes. Pleopods 3–5 endopods with 2 marked depressions. Uropods small relative to body size, rami elongate-oval, subequal in lengt, endopod longer than exopod.

Colour. Female appear white to yellowish-tan in alcohol, with chromatophores scattered posteriorly on the pereon and pleotelson.

Size. Ovig. females 14–18 mm.

Remarks. Ryukyua globosa can be recognised by its broad and ovate body shape, anterior margin of cephalon flexed and produced into pereonite 1, coxae that are much shorter than pleonites and having a rectangular instead of a triangular pleotelson.

Ryukyua globosa attaches to the ventral part of the host branchial cavity, with the cephalon to the anterior end of the host, and with its abdomen or brood pouch directed outwards, facing the branchial operculum ( Williams & Bunkley-Williams 1994; Rameshkumar et al. 2016). Its asymmetrical body when it occupies both sides of the branchial cavity. R. globosa differs from R. circularis : other characters are discussed under the remarks of R. circularis .

The two species of Ryukyua are genus specific to the host Amblygaster , a small group of sardinellas from the family Clupeidae containing three valid species worldwide (Eschmeyer et al. 2018): Amblygaster clupeoides (Bleeker’s smoothbelly sardinella), Amblygaster leiogaster (Smoothbelly sardinella) and Amblygaster sirm (Spotted sardinella). Including this present study, R. circularis is present on all hosts, whereas R. globosa is commonly reported from A. sirm . Although it may not come as a surprise to find R. globosa on A. leiogaster , more reports are needed to clarify the host specificity and infection rate of this parasitic relationship.

With regards to geographical occurrence of this parasite (in relation to the availability of the host), both Ryukyua sp. have a Indo–West Pacific distribution, with both species reported from India ( Rameshkumar et al. 2016, Praveenraj et al. 2017, Vigneshwaran et al. 2018d); Japan for R. globosa and Thailand for R. circularis ( Williams & Bunkley-Williams 1994) .

Distribution. Ryukyua globosa was recorded from Japanese waters ( Williams & Bunkley-Williams 1994) and southeast coast of India ( Rameshkumar et al. 2014a).

Hosts. Known only from family Clupeidae : Amblygaster sirm , Amblygaster leiogaster ( Williams & Bunkley-Williams 1994) and Sardinella gibbosa ( Rameshkumar et al. 2014a) .

Figures

FIGURE 13. a–c, Nerocila sundaica Bleeker, 1857, female (24 mm), (ZSI/MBRC D1-547); d–f, Nerocila trichiura (Miers, 1877), female (30 mm), (ZSI/MBRC D1-548); g–i, Norileca indica (H. Milne Edwards, 1840), female (26 mm), (ZSI/MBRC D1-549); j–l, Norileca triangulata (Richardson, 1910), female (16 mm), (ZSI/MBRC D1-550); m–o, Ryukyua circularis (Pillai, 1954), female (13 mm), (CAS/MBRM C-227); p–r, Ryukyua globosa Williams & Bunkley-Williams, 1994, female (14 mm), (ZSI/MBRC D1-552).