Lesser urn ascidian

Scientific name : Atriolum robustum

Small colonies (max 3 cm), urn-shaped, with relatively large oral siphons around a common cloacal siphon. Variable colour, white with green stains to rust. Often confused with the compound ascidian Didemnum molle. The latter is larger, with more and relatively smaller oral siphons.

Associated organisms
The green colour around the cloaca is due to the symbiotic blue-green algae Prochloron. Often epibiotic on other ascidians Recently we observed the association with an unidentified flatworm, Pseudoceros sp. 7, mimic of A. robustum.