Opisthobranch of the Week Data
Elysia obtusa is considered to be common in Okinawan waters; I've not personally observed this small sacoglossan in the waters of Okinawa's main island, however, Atsushi Ono reports the above featured animal is one of over 50 individuals which he has seen in the Keramas* (pers. comm.). The featured animal was photographed by Atsushi in March of 1997 from an area of dead coral and algae. I've added a second page with an additional photograph of a second Keramas animal, as well as an image of the illustration featured in Baba (1949). The lack of the white line on the parapodia as described below is perhaps an individual variation seen in some of the Kerama animals.
Baba (1938) described the species, but I unfortunately don't have access to his complete species description and I'm citing Carlson & Hoff's (1978) description of the Guam material, in part, as follows:
DESCRIPTION: Animals are moderately thin when crawling. Specimens vary from 3.7 to 10.3 mm in length. The parapodia are held over the dorsum but not together. The short rhinophores are held almost parallel with the substrate and tend to point more laterally than anteriorly. The animal is basically smooth with some small sparse conical projections occurring over the parapodia, head and rhinophores. The rounded, slightly elongate pericardium has two single large veins extending along the lower part of each parapodia.
COLOR ALIVE: The color of the Guam specimens matches Baba's (1938) description and the color plates in Baba (1949). The general body color is a translucent pale green or greenish yellow with a darker green internal pigmentation. This internal pigmentation may be almost totally lacking or to the other extreme, be throughout the whole animal. The conical projections are white as is the edge of the parapodia. The white on the edge of the parapodia tends to be more developed in the inner than the outer edge.
In the Sea Slug Forum there are a series of images of the species and in addition, Rudman (2001) mentions the following in reference to the description and possible synonymy of Elysia obtusa:
Animal translucent yellow with white spots scattered over the body, head and parapodia. Edge of parapodia lined with bright white line. In some animals the green of the digestive gland causes the parapodia to be dark green in colour but from the range of photos in the Forum it appears that the green colouration is probably a temporary colouration dependent on how recently an animal has been feeding. Dark green parapodia probably corresponds to a recently fed animal while predominantly yellow animals have probably not fed for some time. Some authors have identifies this northwestern pacific species with the Caribbean E. flava, but until the anatomy of the two are compared I would think such a synonymy is premature.
In addition to the above featured Elysia obtusa, the following Elysia have been previously featured on these pages:
E. amakusana E. cf. bennettae E. lobata E. mercieri E. ornata E. rufescens E. thompsoni E. cf. tomentosa E. yaeyamana
* Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.