Known only from Massachusetts, USA. [Atlantic coast].
Gloucester, Massachusetts, USA. Photos: Alan Shepard.
The animal is translucent with a reddish brown tinge, and scattered spots and blotches of reddish brown and milky yellow all over the dorsal surface and sides of the body. The reddish brown blotches are spread rather evenly over the dorsum and sides of the body. There are also some yellow blotches scattered everywhere, but the yellow is mainly concentrated in a median line between the rhinophores and the gills and in a dorso-median line along the dorsal foot from behind the gills to the posterior tip. Sometimes the milky yellow line between the rhinophores and gills is replaced by a patch between and just behind the rhinophores.
The mantle edge bears tentacular processes. Around the head there are 4 very long processes, and down each side there are 4 much shorter ones between the rhinophores and gills. Just behind the gills, on each side, there are a pair of median sized tentacles, each pair sharing a common base. There is also a tentacular appendage in the dorsal midline just in front of the gills. There are approximately 12 bipinnate gills. The rhinophores are relatively long, and the upper half is slightly recurved backwards. There are lamellae on the underside of the upper half of each rhinophore. The animal grows to 12mm in length.
Okenia ascidicola is reported by Morse (1972), to be a specific feeder on the solitary ascidian Molgula manhattanensis. It has seldom been found, probably because of its association with its food. It eats through the tough outer skin of the ascidian and nestles in the cavity it makes, leaving only the gills protruding. It has been reported only from Massachusetts on the Atlantic coast of Nth America.
• Morse, M.P. (1972). Biology of Okenia ascidicola spec. nov. The Veliger, 15(2): 97-101.
Rudman, W.B., 2003 (July 17) Okenia ascidicola Morse, 1972. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/okenasci
Eggs of Okenia ascidicola
From: Alan Shepard, December 16, 2003
Okenia ascidicola from Gloucester, Massachusetts, USA
From: Alan Shepard, July 19, 2003