OKINAWAN
OPISTHOBRANCH OF THE WEEK

Glossodoris atromarginata (Cuvier, 1804) 26mm

Opisthobranch of the Week Data

Taxonomy:

Frequency on Okinawa: Collection Data:
[brackets indicate range for all Okinawa-collected specimens of the species]


Species Account:

        Glossodoris atromarginata should be considered to be rare on Okinawa as I have collected a total of only five individuals over a period of more than twenty-five years of diving here. The five individuals were collected from both the same dive site and habitat (mixed live/dead stony coral reef near the reef edge) during the day. One pair of individuals was found within a few cm. of each other (May, '92). I've added a second page showing four additional Okinawa-collected specimens.

        The following partial description of Glossodoris atromarginata is taken from Rudman (1986) in which he makes the comparison of several similarly colored animals of which he considers to be G. atromarginata:

        Colour: Specimens from New South Wales, are usually white, or cream but occasionally pale yellow. The mantle is bordered with a band of a lighter colour, and right at the edge is a black line. The rhinophore pockets are edged with black but the gill pocket is not. The rhinophores have a creamy white stalk and the club is black except for a white tip and a white median line up both the posterior and anterior sides. The gills are translucent white with black dusting forming lines up both edges. The colour range from white to pale yellow can occur in animals from the same locality. The only other colour variation is that the black pigmentation is very occasionally reduced to pale grey. In most specimens the large opaque submarginal mantle glands can be seen.

        In Queensland, off-shore reef specimens are similar in colour to New South Wales animals although a higher proportion are pale yellow. In specimens from coastal Queensland the cream yellow regions are usually covered in a fine dusting of brown giving the body a brownish-yellow appearance. The gills also have a brown dusting as well as black around the edge. In these brownish coastal specimens the opaque white mantle glands are clearly visible. The only specimen available from Papua New Guinea is pale yellow like the off-shore reef specimens.

        In the one specimen from Tanzania the ground colour was a brown yellow ochre, somewhat darker in the midline of the mantle than elsewhere. There are also scattered small straw-coloured spots which are regions where the brown pigment is absent. The scattered, large, opaque submarginal mantle glands are clearly visible. At the edge of the mantle there is a whitish submarginal band and a marginal band of deep violet-black. Between the dark margin and the whitish submarginal band is a diffuse zone of blackish-violet. There is a dark edging, brown rather than black, to each rhinophore pocket, and the rhinophores have a white stalk and black club with an anterior and posterior median white stripe. Each gill is edged with purplish-black, the gill itself being dusted with brown in the bottom half and white in the upper half. There is no dark edging to the gill pocket. A distinctive feature of this E African specimen is scattering of the small ovoid spots of translucent straw colour along the sides of the body as well as on the mantle.

        Shape: The species can be characterized by its high, elongate body, with the mantle extending almost to the posterior end of the foot. The mantle overlap is very reduced but it is thrown into a series of primary folds on each side (usually two between the rhinophores and the gills and one behind the gills), and often many secondary folds as well. In E Australian material from New South Wales and Queensland there appears to be no correlation between colour or geographic locality and degree of mantle folding: some specimens have only the three primary folds on each side while others have complex series of secondary folds. Smaller specimens usually have less folding but the converse is not a general rule as many large specimens have no secondary foldings.

        The specimen from E Africa is of similar shape with three primary folds on each side and several secondary folds.

        In all forms the gills are simple. They are arranged in an arc, opening posteriorly, around the anus, and each end of the arc curves inwards to form a secondary spiral. The gills move rhythmically.

        Marshall & Willan (1999) point out that Glossodoris atromarginata feed on several species of siliceous sponges belonging to the families Spongiidae and Irciniidae.

Literature Cited:


Page Date: 03 May '04
Page Modification Date: 03 May '04
Digitally manipulated photo
Copyright © 2004 Robert F. Bolland