Urn ascidian

Scientific name : Didemnum molle

Soft, urn shaped, colonies, more rarely encrusting or lobed, diameter 5-10 cm. The common cloacal opening is very large compared to the many, tiny, oral siphons scattered all upon the colony.
Often confused with another compound ascidian, Atriolum robustum. This latter is normally smaller, with less abundant, larger, oral siphons.
Lobed colonies are often encountered. Even if they are clearly sessile animals, Didemnum molle colonies can make small changes of position. They grow basal filaments that are anchored to the bottom next to the colony, and pull it to the new position.

Associated organisms
The dark green colour of the cloacal opening and of irregular stripes is due to a symbiotic blue-green algae (Prochloron).