Pleopodias diaphus Avdeev, 1975

Hadfield, Kerry A. & Smit, Nico J., 2017, Revision of the fish parasitic genus Pleopodias Richardson, 1910 (Isopoda, Cymothoidae), with the description of a new species and key to the genus, ZooKeys 667, pp. 21-37 : 22-24

Pleopodias diaphus Avdeev, 1975

Pleopodias diaphus Avdeev, 1975: 254-256, figs 1-11.-Bruce & Harrison-Nelson, 1988: 600.-Trilles, 1994: 109.-Yamauchi, 2009: 477-479, figs 7-8.

Pleopodias superatus Williams & Williams, 1986: 656, figs 62-68.

Material examined.

Female holotype of Pleopodias superatus (26.5 mm TL, 10.4 mm W), caught in a shrimp net off Honshu Island, Japan, 11 April 1969 (USNM 231069).

Holotype. Non-ovigerous female, collected from the East-China Sea (Sea of Japan), from the body of Diaphus coeruleus (TINRO AGK 74190). Paratypes. Non-ovigerous females, same information as holotype (TINRO APK 74191-74195). Not examined.

Description.

Female holotype of Pleopodias superatus . Length 26.5 mm, width 10.4 mm.

Body oval, 2.4 times as long as greatest width, dorsal surfaces smooth and polished in appearance, widest at pereonite 5, most narrow at pereonite 1, lateral margins subparallel. Cephalon 0.8 times longer than wide, visible from dorsal view, subtriangular. Frontal margin truncate, thickened and ventrally folded. Eyes oval with distinct margins; one eye 0.3 times width of cephalon, 0.4 times length of cephalon. Pereonite 1 smooth, anterior border slightly indented, anterolateral angle narrowly rounded, extending to middle of the eye. Posterior margins of pereonites 1-4 smooth and straight, 5-7 slightly curved laterally, posterior margin of pereonite 7 produced medially. Coxae 2-3 narrow, with posteroventral angles rounded; 4-7 small and narrow, not extending past pereonite margin. Pereonites 1-5 increasing in length and width; 6-7 decreasing in length and width. Pereonite 7 partially overlapping pleonite 1. Pleonites posterior margin smooth, mostly concave. Pleonite 1 widest, visible in dorsal view. Pleonite 2 not overlapped by pereonite 7; posterolateral angles of pleonite 2 narrowly rounded. Pleonites 3-5 progressively getting smaller; pleonite 5 not overlapped by lateral margins of pleonite 4, posterior margin slightly concave. Pleotelson 1.8 times as long as anterior width, dorsal surface slightly depressed, lateral margins straight, posterior margin with medial notch.

Antennula thinner and shorter than antenna, contiguous bases, consisting of 8 articles; peduncle articles 1 and 2 distinct and articulated; articles 2-3 expanded; extending to pereonite 2. Antenna consisting of 12 articles; extending to middle of pereonite 3. Pereopod 1 basis 1.6 times as long as greatest width; ischium 0.7 times as long as basis; merus proximal margin without bulbous protrusion; carpus with straight proximal margin; propodus 1.2 times as long as wide; dactylus slender, 1.5 times as long as propodus, 2.4 times as long as basal width. Pereopod 7 longer than other pereopods, basis 2.2 times as long as greatest width; ischium 0.8 times as long as basis, without protrusions; merus proximal margin without bulbous protrusion, 1.2 times as long as wide, 0.5 times as long as ischium; carpus 0.9 times as long as wide, 0.4 times as long as ischium, without bulbous protrusion; propodus with numerous acute robust setae, 2.6 times as long as wide, 0.8 times as long as ischium; dactylus slender, 0.8 times as long as propodus, 3.3 times as long as basal width. Uropod longer than the pleotelson, rami subequal. Endopod apically rounded. Exopod apically narrowly rounded.

Distribution.

Sea of Japan ( Avdeev 1975) and off Honshu, Japan ( Williams and Williams 1986; Yamauchi 2009).

Hosts.

Anterior to the dorsal fin of Diaphus coeruleus (Blue lantern fish) ( Avdeev 1975).

Remarks.

Pleopodias diaphus has an ovate shape, contiguous antennula bases, and an emarginated pleotelson posterior margin. The uropod rami are approximately the same length and the eyes are large (each eye approximately a third of the cephalon width).

It was originally described from Japan, with several drawings and a brief description in Russian. In 1986, Williams and Williams described a new species, Pleopodias superatus which shared many similarities with P. diaphus . After comparisons of the notched pleotelson as well as the antennae and somatic morphology, Bruce and Harrison-Nelson (1988) synonymised it with P. diaphus . Despite numerous attempts, the type specimens of P. diaphus could not be obtained for inclusion in the present study; however, the types do exist and the species is eminently recognisable from the original illustrations and is therefore not a nomen dubium or species inquirenda. Avdeev (1975) reported the types as immature females but both the size and drawings indicate they are still adult females (non-ovigerous) and therefore suitable for a valid species description. Both species ( P. diaphus and P. superatus ) are well illustrated, readily recognised, from the same region, and appear identical, thus the synonymy of the two species by Bruce and Harrison-Nelson (1988) is here upheld until a detailed redescription of the original type material of P. diaphus indicates otherwise.

As the type material for P. diaphus could not be obtained the redescription provided here is based on the holotype of P. superatus housed at USNM. This redescription includes updated measurements and characteristics which are comparable to the other Pleopodias species in this paper. This modern description of the type material of P. superatus will also aid future research into its current status as junior synonym of P. diaphus .

Pleopods and mouthparts of specimens identified as P. diaphus were drawn and described by Yamauchi (2009). The specimens Yamauchi (2009) examined largely conformed to the above description; however, the body size differed with the three more recent samples (12-27 mm in length) being more slender (3.4-3.9 times as long as wide).