Opisthobranch of the Week Data
Chelidonura tsurugensis is considered to be very rare here as I have seen and collected a total of only three individuals, two from Seragaki and one from Onna Flats. The above featured individual was found crawling on top of a patch of mixed silty-sand and strewn coral rubble. The second collected specimen was found at the reef edge of a primarily dead stony coral reef, crawling in the open. The bright yellow or orange spots upon the black notum separate this small aglajid from all other species found in the waters of Okinawa's main island. I've added a second page showing an image of an orange-spotted specimen, which is the third animal I've seen and collected here. This third animal was collected from the Intertidal during a daytime spring tide; it was found along with a relatively large series of other cephalaspids (4 Metaruncina setoensis(?), 4 Chelidonura hirundinina, and 24 small black Chelidonura sp.). These were all found in an area approximately seven meters by seven meters and crawling on the surface of silty-sand.
I've taken the following description of C. tsurugensis from the original paper by Baba & Abe (1959):
Animals 15-20 mm in total length. Mantle-shield bifurcated behind, the left lobe long and tapering, the right one in all specimens shorter and rounded. General body colour a glossy purplish black. The whole upper surface except the sole is covered with a varying number of yellow or golden-yellow spots, very irregular in size and in arrangement. An opaque white marking at the anterior edge of the head-shield on each side. Parapodial lobes without a coloured border.