Cymothoa rotunda Avdeev, 1979

Martin, Melissa B., Bruce, Niel L. & Nowak, Barbara F., 2016, Review of the fish-parasitic genus Cymothoa Fabricius, 1793 (Crustacea: Isopoda: Cymothoidae) from Australia, Zootaxa 4119 (1), pp. 1-72 : 43-46

Cymothoa rotunda Avdeev, 1979

Figures 27–28

Cymothoa rotunda Avdeev, 1979a: 223 , pl. 1. — Trilles, 1994: 148. — Kensley, 2001: 233. — Bruce, Lew Ton & Poore, 2002: 176. — Trilles & Bariche, 2006: 228.

Material examined. Holotype: 1 ovig. ♀ (31 mm), from the Indian Ocean off Western Australia (precise locality not given), from long-tailed catfish Euristhmus lepturus (Günther, 1864) ( TINRO АGK 75010).

Ovigerous female Length 31 mm width 20 mm (holotype).

Body ovoid, 1.4 times as long as greatest width, dorsal surface rough, laterally dome-shaped, widest at pereonite 4, most narrow at pereonite 1. Cephalon subtriangular, 0.9 times longer than wide, visible from dorsal view. Frontal margin rounded to form blunt rostrum, ventrally folded. Eyes absent. Pereonite 1 anterolateral margins broad, unique bulbous ornamentation; posterior margins of pereonites irregular; pereonites 5–7 subequal in length, posterolateral margins arched. Coxae 2–7 posteroventral margins rounded. Pleonite 1 visible in dorsal view; pleonites 3–5 posterior margin bisinuate, subequal in width. Pleotelson 0.4 times as long as anterior width, lateral margin weakly convex (right lateral margin damaged exposing pleopods), posterior margin rounded, without median point.

Antennula comprised of 7 articles; peduncle articles 1 and 2 distinct and articulated; article 2 1.3 times as long as article 1; article 3 0.6 times as long as combined lengths of articles 1 and 2, 1.3 times as long as wide. Antenna comprised of 8 articles, article 3 1.1 times as long as article 2, 1.0 times as long as wide; article 4 1.0 times as long as wide; article 5 1.0 times as long as article 4, terminal article without setae, extending half of pereonite 1. Labrum anterior margin broad and convex.

Pereopod 1 basis 1.7 times as long as greatest width, superior proximal margin smooth, without raised carina; ischium 0.5 times as long as basis; merus proximal margin without bulbous protrusion; carpus proximal margin straight; propodus 1.1 times as long as wide; dactylus narrow, 1.7 times as long as propodus, 3.1 times as long as basal width. Pereopod 2 basis 1.6 times as long as greatest width, superior proximal margin smooth, without raised carina; propodus 1.0 times as long as wide; dactylus 1.2 times as long as propodus. Pereopods 3–5 similar to pereopod 2, gradually increasing in size, without robust or simple setae. Pereopod 6 basis 1.2 times as long as greatest width, superior proximal margin smooth, with slightly raised carina; ischium 0.6 times as long as basis, propodus 1.0 times as long as wide, dactylus 1.6 times as long as propodus. Pereopod 7 basis 1.6 times as long as greatest width, superior proximal margin smooth, with raised carina; ischium 0.5 times as long as basis, with bulbous protrusion; merus proximal margin with slight bulbous protrusion, merus 0.5 times as long as ischium, 0.6 times as long as wide; carpus 0.2 times as long as ischium, with slight bulbous protrusion, 0.2 times as long as wide; propodus 0.6 times as long as ischium, 1.2 times as long as wide; dactylus narrow, 1.8 times as long as propodus, 2.8 times as long as basal width.

Pleopod 1 exopod 1.0 times as long as wide, lateral margin convex, distally broadly rounded, mesial margin straight; endopod 1.1 times as long as wide, lateral margin weakly convex, distally broadly rounded, mesial margin straight; peduncle 2.0 times as wide as long.

Uropod not extending beyond posterior margin of pleotelson; peduncle 1.7 times as long as greatest width, 0.7 times as long as exopod, lateral margin without setae, marginal setae absent, apices narrowly acute, lateral margin straight, mesial margin straight. Exopod subequal in length to endopod, 2.9 times as long as greatest width, apically rounded, lateral margin straight, terminating without setae, mesial margin weakly straight. Endopod 2.9 times as long as greatest width, apically rounded, lateral margin weakly convex, terminating without setae, mesial margin straight.

Colour. Greenish yellow.

Remarks. Cymothoa rotunda can be distinguished by the ovoid body (1.4 times longer than wide), widest and longest at pereonite 4; cephalon subtriangular; frontal margin ventrally folded; pereonite 1 anterolateral margins broad and tapers to a narrow point that reaches the rostrum, with unique bulbous ornamentation; pleon shape appearing horizontally suboval; uropods not reaching pleotelson posterior margin; and pleotelson posterior margin rounded. Avdeev’s (1979a) illustration of the ovigerous female also included: simple maxillula, with 3 terminal setae; lateral lobe of maxilla partly fused to mesial lobe, with 1 and 2 recurved setae on mesial lobe and lateral lobe respectively; weakly segmented maxilliped, terminal article 3 with 2 recurved setae; pleopod 2 with appendix masculina present, exopod bigger than endopod, convex endopod mesial margin, distally rounded, deeply convex lateral margins, without proximal margins extending beyond peduncle.

Cymothoa rotunda is similar to C. hermani and C. borbonica from the subtriangular cephalon and rounded pleotelson posterior margin (and bulbous ornamentation in C. hermani ). Cymothoa hermani differs from C. rotunda from the less rounded body, 1.8 to 1.9 times longer than wider (compared to the 1.4 times longer than wide body), dorsally visible coxae and trisinuate posterior margin of pleonites 2–5. The female paratype of C. hermani has 4 robust setae on the maxillula and pleopod 2 without an appendix masculina ( Hadfield et al. 2011) compared to the 3 robust setae on maxillula and pleopod with an appendix masculina of C. rotunda ( Avdeev 1979a) . Cymothoa borbonica does not have the unique bulbous ornamentation on pereonite 1, body sub-parallel, pleonites not subequal in width, and coxae 2–7 posteroventral margins acute and dorsally visible.

Distribution. Western Australia ( Avdeev 1979a); known only from the original description.

Hosts. Only known from the family Plotosidae : long-tailed catfish Euristhmus lepturus (Günther, 1864) (see Avdeev 1979a).

Figures

FIGURE 27. Cymothoa rotunda, ovigerous holotype (31 mm; AGK 75010). A, dorsal view; B ventral view of mouthpart; C, antennula; D, antenna; E, uropod; F, front view of pereonite 1 and cephalon; G, lateral view.

FIGURE 28. Cymothoa rotunda, ovigerous holotype (31 mm; AGK 75010). A – D, pereopods 1, 2, 6, 7 respectively; E, pleopod 1; F, dorsal view of pleotelson.