Sebadoris fragilis (Alder & Hancock, 1864)

Location: Kabirawan, Ishigaki and Yaeyama, Okinawa, Japan
Date: 2018/04/27
Length: 200mm
Depth: 7.0m
Water temperature: 22.0℃

Description

A large dorid reaching 5 to 6 inches (ca. 13–15 cm) in body length. The body is broadly oval, depressed, brownish. The mantle is ample, firm, covered with minute, somewhat scattered, spiculose, blunt tubercles of unequal sizes, rather paler than the ground — which is yellowish brown, beautifully marbled with darker brown and white, and covered with minute dark freckles. The under surface is strongly blotched with reddish brown, the blotches becoming confluent near the foot and fewer towards the margin, which is pale. The dorsal tentacles are conical, finely laminated on the upper part, the laminae meeting in front, dark yellowish, much and minutely freckled, especially below; retractile within short sheaths. The oral tentacles are linear, pointed. The branchial plumes are six, large, quadripinnate, minutely speckled with dark brown; the circle open behind; the anus large and tubular. The foot is broad, ovate, reddish brown, with darker blotches, and pale towards the margin; it is deeply grooved in front, but not notched, the posterior end short and rounded. The radula is as in Doris tuberculata, with a prehensile collar. Spicula are very numerous, small, and rather irregular in form, but usually bent in the centre, with the extremities obtuse, sometimes a little enlarged. Walter Elliot informed the authors that the species "is so brittle that it breaks to pieces even when alive" — hence the specific epithet. The two preserved specimens are much mutilated. The species resembles Doris bellicosa Kelaart in colouration but differs in size, colour, and the obtuse form of the tubercles. The spawn is white and forms a single irregular coil with the free margin much contorted.

Distribution

Type locality: Waltair, near Vizagapatam, Coromandel coast, Madras Presidency, India (now Visakhapatnam, Andhra Pradesh). Based on specimens collected by Walter Elliot in 1853–1854. The species has subsequently been recorded from Madagascar, Tanzania, Japan, the Philippines, and Papua New Guinea.

Etymology

The specific epithet fragilis is Latin for "fragile, brittle", reflecting Walter Elliot's report to the authors that the species "is so brittle that it breaks to pieces even when alive."

Remarks

In the original description Alder & Hancock placed the species in Doris. The species was later transferred to Sebadoris Marcus & Marcus, 1960 (the parentheses in the author citation reflect this generic transfer). Discodoris concinna is a synonym. The species is often confused with Tayuva lilacina, but can be distinguished by examining the ventral (rather than dorsal) markings.