(Müller, 1776)
Description
External appearance
Solitary, body oval to subquadrate and laterally compressed, up to about 50 mm high, attached to substratum by a small part of the base. Test firm, thin, smooth and almost transparent. Mantle with yellow, white and red markings, clearly visible through the test.
Characters
Oral siphon with 6-8 lobes and placed terminal; atrial siphon 6-lobed and located close to the oral siphon. The siphons bear red ocelli. There are numerous long, simple branchial tentacles. Branchial sac with numerous rows of stigmata; no folds; with up to 27 longitudinal bars on each side but without papillae at the intersections with transverse vessels. Stigmata are of variable length, curved, and arranged in subquadrate spirals. Gut to the right of the branchial sac; stomach with longitudinal folds. Male and female gonads are diffusely distributed on both sides of the gut loop (C. parallelogramma morphology).
Habitat
Attached to hard substrata; from shallow water to depths of 200 metres;
Distribution
From Norway to the Mediterranean.