Botryllus schlosseri (Pallas, 1766)  

This species is a compound, colonial ascidian, with small, bean-shaped zooids embedded in a common matrix or tunic. The colony grows to form encrusting patches that typically reach 3-4 mm in thickness and 2-10 cm in diameter. Individual zooids lie horizontally relative to the substrate, and are organized into radial, star-shaped clusters or "systems", with each system measuring 0.5-1 cm in diameter. Each zooid grows up to 5 mm in length. Zooids are characterized by a pharynx with 9-10 rows of stigmata, and a hood that covers the opening of the atrial siphon. Color varies among colonies, but often includes a combination (=bi-colored) of yellow, orange, red, brown, grey, or black.