Description: A colonial ascidian forming compact sheets. Zooids are elliptical and are arranged in star-systems around common cloacal openings, with typically 6-10 zooids in a system. 6 mm thick x 70 mm wide sheets.

Habitat: A common ascidian, occurring on seaweeds and kelp stipes in shallow water, and on exposed rock surfaces. Commonest in places with considerable wave or current exposure.

Distribution: Probably widespread and common all round the British Isles.

Similar Species: Recently split from Botryllus schlosseri, which is a species complex.

Key Identification Features:

• Honeycomb-like arrangement of zooid systems.
• Colour blue or yellow.
• Small red spot adjacent to oral siphon.

iNaturalist: Botryllus renierii at iNaturalist World Species Observations database.

WoRMS: Botryllus renierii at World Register of Marine Species.