Pleopodias elongatus Richardson, 1910

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 : 24

Pleopodias elongatus Richardson, 1910

Pleopodias elongatus Richardson, 1910: 26-27, fig. 25.-Nierstrasz, 1931: 133.-Avdeev, 1975: 89, fig. 3.-Bruce, 1987: 89, fig. 3.

Material examined.

Holotype. Ovigerous female (20 mm), off Matocot Point, Philippine Islands, 8 June 1908, 170 fathoms (= 311 m depth), station 5268, coll. U.S. Bureau of Fisheries Albatross Philippine Expedition 1907-08 (USNM 40917). Also noted: bottom third of the pleotelson folded in.

Description.

Female holotype. Length 20 mm, width 7.5 mm.

Body elongate, 2.7 times as long as greatest width, dorsal surfaces smooth and polished in appearance, widest at pereonite 4 and pereonite 5, most narrow at pereonite 1, lateral margins subparallel. Cephalon 0.7 times longer than wide, visible from dorsal view, subtriangular. Frontal margin thickened, ventrally folded and truncate. Eyes oval with distinct margins, one eye 0.25 times width of cephalon; 0.4 times length of cephalon. Pereonite 1 smooth, anterior border straight, anterolateral angle acute, anteriorly produced, extending to one third of the eye. Posterior margins of pereonites smooth and slightly curved laterally. Coxae 2-4 narrow, with posteroventral angles rounded; 5-7 small and narrow, not extending past pereonite margin, with posteroventral angles curved. Pereonites 1-4 increasing in length and width; 5-7 decreasing in length and width. Pleonites posterior margin smooth, mostly concave. Pleonite 1 widest, visible in dorsal view. Pleonite 1 and 2 not overlapped by pereonite 7; posterolateral angles of pleonite 2 rounded. Pleonites 3-5 progressively getting smaller; pleonite 5 not overlapped by lateral margins of pleonite 4, posterior margin straight. Pleotelson 1.6 times as long as anterior width, dorsal surface slightly depressed, lateral margins weakly convex, posterior margin rounded and damaged.

Antennula thinner than antenna, length longer than antenna, bases narrowly separated, consisting of 8 articles; peduncle articles 1 and 2 distinct and articulated; articles 2-3 expanded; extending to middle of pereonite 1. Antenna consisting of 11 articles; extending to middle of pereonite 2. 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 1.4 times as long as wide; dactylus moderately slender, 1.3 times as long as propodus, 2.4 times as long as basal width. Pereopod 7 longer than other pereopods, basis 2.3 times as long as greatest width; ischium 0.8 times as long as basis, without protrusions; merus proximal margin without bulbous protrusion, 1.3 times as long as wide, 0.4 times as long as ischium; carpus 1.3 times as long as wide, 0.4 times as long as ischium, with slight bulbous protrusion; propodus 3.3 times as long as wide, 0.8 times as long as ischium; dactylus slender, 0.9 times as long as propodus, 3.7 times as long as basal width. Uropod longer than the pleotelson, rami subequal. Endopod apically slightly pointed. Exopod apically narrowly rounded.

Hosts.

Not known.

Distribution.

Philippine Islands ( Richardson 1910; Bruce 1987).

Remarks.

Pleopodias elongatus can be distinguished by the small eyes (each eye a quarter of the cephalon width), antennula bases narrowly separated, antenna extending to the middle of pereonite 2, rounded pleotelson, and uropod rami approximately the same length.

The only other species recorded from the Pacific is P. diaphus (from Japan). Pleopodias elongatus differs from P. diaphus in having antennula bases narrowly separated ( P. diaphus bases in contact), shorter antenna ( P. diaphus antenna extend to posterior of pereonite 3), absence of robust setae on propodus of pereopod 7 ( P. diaphus has numerous acute robust setae), a rounded pleotelson ( P. diaphus pleotelson subquadrate with a deeply emarginated medial notch), and smaller eyes ( P. diaphus eyes cover a third of the cephalon width).