Description: This ascidian forms extensive loosely attached sheets over other sessile animals, such as bryozoans and sponges. The sheets are wrinkled, with regularly scattered small inhalant pores and irregular larger exhalant openings, usually on raised parts of the colony. The usual colour is a dirty off-white or beige. Colonies may become free hanging, growing out from their support on overhanging surfaces. 3mm thick x 150mm across.

Habitat: A common ascidian on the lower shore and in shallow water.

Distribution: Widespread around the British Isles

Similar Species: Could easily be confused with Didemnum maculosum or Lissoclinum perforatum. Trididemnum delesseriae forms smaller colonies on sublittoral algae.

Key Identification Features:

• Loosely attached bubbly sheets.
• Opaque appearance, off-white colour.
• Structure of zooids with 3 rows of stigmata (other didemnids have 4 rows).

Distribution Map from NBN: Trididemnum cereum at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Trididemnum cereum at iNaturalist World Species Observations database.

WoRMS: Trididemnum cereum at World Register of Marine Species. Accepted name: Trididemnum cereum (Giard, 1872). AphiaID: 103594.

Classification: Biota; Animalia; Chordata; Tunicata; Ascidiacea; Aplousobranchia; Didemnidae; Trididemnum