(Pallas, 1766)
Description
External appearance
Colonial, with zooids immersed. Colony forming flat circular or elongate sheets, up to 5 cm long and 2 cm broad. Colour of test variable but often blue. Zooids arranged in star-shaped systems of 3 to 12 individuals and colour in contrast with common test (B. schlosseri yellow).
Characters
Zooids up to 3 mm in length; body not divided into thorax and abdomen. Oral siphon unlobed; atrial siphon long and broad, tapering into a narrow tube. Up to 16 simple branchial tentacles of variable length. Branchial sac with 7 to 15 rows of straight stigmata; three longitudinal bars on each side; no folds. Gut left of branchial sac; stomach short with 8 to 9 longitudinal folds. Mulberry-like testes on each side in mantle; ovaries lateral to testes, with one to four ova (B. schlosseri zooid).
Habitat
Attached to hard substrata; mainly in shallow water but occasionally to depths of several hundred metres;
Distribution
From Norway to the Mediterranean.