Opisthobranch of the Week Data
Baba (1930) described Herviella yatsui (originally as Cratena yatsui) from three specimens (6~12mm) collected from Zusi, Sagami Bay. Baba chose the specific name as a dedication to Professor Naohide Yatsu.
The following is from Baba's original description (1930) of H. yatsui:
Externals: Length of body 6 mm (small specimen) to 12 mm (large specimen). Antero-lateral corners of the foot rounded. Labial tentacles slender, moderately long. Rhinophores shorter, slender and slightly constricted along the whole length. Branchial papillae in 8 to 9 oblique rows on either side, containing about 9 in the first, 1 in the eighth or ninth. Genital opening between the first and second, anus between the second and third branchial rows on the right side.
Colour: Labial tentacles and rhinophores black except for the tips. Black spotted with black or pale black on a transparent, colourless ground. Branchial papillae veined with pale green. Each papilla with an opaque white band and a pale black band, sometimes spotted with black near the tip. Back, tail and head coarsely spotted with opaque white.
Internals: Radula formula 15 x 0.1.0. Tooth with five denticles on each side of the central spine. Masticatory processes of a pair of jaws with about 19 denticles each.
Remarks: This species is clearly distinguished from the other forms of the same genus by the peculiar colouration of the body. In the coloration of the head the present species somewhat resembles Cratena cucullata Bergh, but differs from the latter in having the black points on the back and papillae, and also fewer denticles on the tooth.
Baba (1966) provides a considerably more detailed description of the species in his 1966 publication.
Herviella yatsui is currently unknown from Okinawa's main Island as of late-March, 2002. The close proximity of the main island of Okinawa to the Kerama Islands, as well as the similar opisthofauna to that of the Kerama Islands, suggests the possibility that it is also present here on Okinawa proper. The above featured animal is one which was photographed in the waters of Zamami Island, one of a series of islands in the Kerama Islands Group, which are located 30 ~ 40 kilometers west of the Okinawa capitol, Naha. The featured animal was photographed by Atsushi Ono during March of 1999, in intertidal waters, on the underside of a rock lying on mud. Atsushi's photograph is used here with his kind permission and he considers the species to be rare; Atsushi reports (per. comm.) seeing approximately five others in the Keramas. I've added a second image of H. yatsui showing a bit of color variation of the species. This additional image is also furnished by Atsushi.
The food of H. yatsui is unknown but Marshall & Willan (1999, p. 148) mention that a congeneric species, H. mietta, probably feeds on thecate hydroids.