Roboastra gracilis (Bergh, 1877) {size unrecorded, ca. 15mm}

Opisthobranch of the Week Data


Frequency on Okinawa: Collection Data:
[brackets indicate range for all Okinawa-collected specimens of the species]

Species Account:

        The type locality from which Bergh (1877) originally described the species (as Nembrotha gracilis) is the Philippines. The species was collected for the first time in Japan (as N. gracilis) in November of 1939 from Sagami Bay (Baba, 1949). More recently, Baba (1977), described Roboastra gracilis as being collected from Seto, Japan; this later paper describes in more detail, both the color and radulae of this small infrequently seen animal. Baba's color description of R. gracilis is consistent with the Okinawan material, i.e., the orange yellow stripes of the mantle (the pair of median, pair of dorso-lateral, and the three or four variable lateral stripes of the mantle).

        Roboastra gracilis is superficially similar to another stripped polycerid found on Okinawa, Roboastra luteolineata, but the three elongate simple gills of R. gracilis serve to quickly distinguish the two from each other.

        Roboastra gracilis is considered to be rare on Okinawa as I've collected a total of nine individuals since the initial specimen was collected on 23 April of 1989. The above featured animal was found during a daytime SCUBA excursion crawling in the open on the surface of mixed sand and coral rubble.

Literature Cited:

Page Date: 01 Mar '99
Page Modification Date: 22 Oct '01
Digitally manipulated photo
Copyright © 2001 Robert F. Bolland