Opisthobranch of the Week Data
Atsushi Ono considers Cuthona yamasui to be very rare in the waters of the Keramas*. Atsushi reports seeing only the above single uncollected animal. This featured animal was found by Atsushi in eighteen meters of water on a rock at the base of hydroids and the image of this animal is used here with Atsushi's kind permission.
Hamatani (1993) described Cuthona yamasui from an animal from Okinawa (southwestern Japan) in which the head was orange and white pigmentation consisted of scattered, irregular shaped and sized white patches. It was described as having a ground color which was translucent or colorless or light orange-yellow. The head, oral tentacles and rhinophores were orange red, and over the dorsal and lateral surfaces of the body behind the rhinophores there were numerous irregular opaque white patches. There was a prominent white median band on the head between the rhinophores which extended anteriorly to the lower halves of the oral tentacles and laterally to the outer sides of the rhinophores. The tips of the oral tentacles and rhinophores were white. The upper portion of the cerata were tinged with reddish orange and there was a small white ring below the protruded tip of each ceras. The lower portion of the ceras was covered with clusters of opaque white dots. Hamatani (1993) points out that it was found feeding on the hydroid Aglaophenia cupressina.
C. yamasui seems to be quite variable in color, as shown on Bill Rudman's Sea Slug Forum (numerous links here) as well as on Mike Miller's site.
I've not found Cuthona yamasui in the waters of Okinawa's main island as of the current date. In addition to the above featured animal I've previously featured on these pages the following species of Cuthona:
C. acinosa C. diversicolor C. ornata C. sibogae C. pupillae C. purpureoanulata C. sp. 1 C. sp. 2 C. sp. 3 C. sp. 4 C. sp. 5
* Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.