Opisthobranch of the Week Data
Elysia mercieri is considered to be rare on the main island of Okinawa in as much as I've collected only a single 5mm specimen. The above featured animal is one which was photographed in the waters of Aka 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 December of 1998, on the reef in 5m of water. Atsushi's photograph is used here with his kind permission and he considers the species to be uncommon in the Kerama Islands; Atsushi reports (per. comm.) seeing in excess of ten individuals in the Keramas, but none were collected. A second animal of the species from the Keramas is also illustrated.
The following description and remarks concerning Guam Elysia mercieri are taken from Carlson & Hoff (1978):
DESCRIPTION: Animals are very distinctive having two pairs of very long branched processes extending upward from the edge of the parapodia. The animals are very small, varying in length from 2.4 to 6.5 mm. The parapodia are sometimes held together and sometimes held open only between the pairs of projections. The body surface is covered with smaller unbranched projections. The rhinophores are very long and thin, becoming almost pointed at he tip. The pericardium is very small. When crawling the animal moves with a jerking motion. The eye spots are rounded, black, and protrude.
REMARKS: Although the Guam animals have only two pairs of projections whereas Pruvot-Fol's animals have four pairs, we believe them to be the same since Elysia mercieri is the only Elysia described with long branched processes. The projections are obviously seen even on the preserved specimens.