Platylepas hexastylos Fabricius 1798

Platylepas hexastylos (Fabricius, 1798)

(Figs. 2 F, 14, 15)

Lepas hexastylos Fabricius, 1798: 35, pl. 10, figs 1–2. (not seen)

Coronula bissexlobata De Blainville, 1824: 379, tab 117, fig. 1.

Platylepas bissexlobata.— Darwin 1854: 428, pl. 17, figs. 1a–d. — Weltner 1897: 253. — Gruvel 1905: 276, fig. 300.

Platylepas hexastylos.— Pilsbry 1916: 285, pl. 67, figs. 1–1c. — Broch 1924: 18, fig. 6. — Hiro 1936: 319. — 1937b: 472, fig. 43. — Kolosvàry 1943: 101. — Henry 1954: 444. — Stubbings 1967: 300. — Utinomi 1959: 384. — 1970: 360. — Newman & Ross 1976: 44. — Ren 1980: 188, fig. 2 pl. 1. — Liu & Ren 2007: 312, fig. 138. — Ross & Frick, 2011: 62. — Hayashi 2012: 117: fig. 7.

Material examined. RUMF-ZC-1561, ten specimens (BD 3.08–5.38 mm); collected from a dead sea turtle, Chelonia mydas, in a gill net, Tomari Port, 19 Nov. 2009.

Diagnosis. Shell white; 6 tubiferous plates, externally with horizontal growth ridges, internally with median longitudinal sulcus.

Description. Shell white, conical, low, outer margin of plates serrated, surfaces with horizontal growth ridges (Fig. 2 F, 14A), plates tubiferous, with median longitudinal sulcus of inner surface visible from basal view (Fig. 14 A, B), line of median longitudinal sulcus obvious, dividing each plate into two main lobes (Fig. 14 A); radii narrow. Orifice narrow, oval shaped (Fig. 2 F). Scutum rectangular, wider than high. Tergum triangular, occludent margin and basal margin forming obtuse angle.

Maxilla sub-triangular, serrulate setae apically (Fig. 14 C). Maxillule without notch, cutting margin straight, 2 large setae at upper margin followed by 8 smaller, simple setae (Fig. 14 D). Mandible with 5 main teeth, second, third and fourth bifid, secondary tooth between second and third, and third and fourth; inferior angle pectinated, covered with fine pectinations (Fig. 14 E, F). Mandibular palp oval; lateral margin covered with long, fine setae; upper margin with short, fine setae (Fig. 14 G). Labrum notched, 3 large teeth on either side of cutting margin (Fig 14 H).

Cirrus I with rami unequal, anterior and posterior rami 7- and 10-segmented, respectively, both rami with serrulate setae (Fig. 15 A, B). Cirrus II with anterior and posterior rami 7-segmented (Fig. 15 C); both rami with serrulate setae. Cirrus III with anterior and posterior rami 9- and 12-segmented (Fig. 15 D). Cirri IV to VI long, slender (Fig. 15 E), intermediate segments of posterior ramus of cirrus IV (Fig. 15 F) and cirrus VI (Fig. 15 G) with 3 pairs of long serrulate setae with very fine setules and 1 pair of shorter, simple setae.

Penis long, length about 1.5 times length of cirrus VI; pedicel with small basi-dorsal point (Fig. 15 H).

Distribution. Cosmopolitan in temperate and tropical waters; attached to the carapace, plastron, head, flipper, legs and soft skin of sea turtles.

Remarks. In Japanese waters, P. h e x a s t y l o s has been recorded on the Loggerhead turtle Caretta caretta (Linnaeus, 1758) in Niigata (Utinomi 1970b), Iwate, Fukui, Okinawa, Kagoshima, Hachijojima Island and Chiba (Hayashi 2012), on the Green turtles Chelonia mydas (Linnaeus, 1758) in Okinawa, Ogasawara Island, Wakayama and Kanagawa (Hayashi 2012), on the Black turtle Chelonia mydas agassizii (Bocourt, 1868) in Iwate (Hayashi et al. 2011), on the Hawksbill turtles Eretmochelys imbricata (Linnaeus, 1766) in Chiba, Fukui and Okinawa (Hayashi 2012) and on the Leatherhead turtle Dermochelys coriacea (Vandelli, 1761) in Niigata and Ishikawa (Utinomi 1970b).