A dark encrusting colony - black through deep purple, sometimes with orange around the siphons - in which the animals are laid out in meandering double rows rather than the neat stars of its relative. It covers shaded rock, wreck plating and harbour walls in sheets up to about 20 cm (8 in).
This is one of the world's more successful hitchhikers, carried between ports on hulls and now established well outside its original range, which is why identifying it anywhere involves the question of where it actually came from. Unlike most ascidians it broods its larvae inside the colony and releases them ready to settle within hours, so a fouled hull seeds a new harbour quickly. On natural reef here it takes shaded, sheltered surfaces, and a colony overgrowing dead coral will sometimes be found being eaten by a nudibranch specialised on exactly this prey.
- dark encrusting sheet with animals in meandering double rows
- black to deep purple, sometimes with orange siphon rims
- surface smooth and slightly glossy when submerged
- colonies up to 20 cm across
