Invasive tunicate, encrusting Mytilus shell
The "sand sponge" tunicate. Numerous individuals including very large specimens (30 cm across)
Colony growing on MBL dock line.
The brain or burned cabbage ascidian Trididemnum cerebriforme at Riy Banks, Algoa Bay , South Africa
Common fouling organism from Europe. Compare with Botrylloides, which can also be golden orange, but generally doesn't form radial, star-shaped colonies. Excellent description and record of introductions at http://www.exoticsguide.org/botryllus_schlosseri
Left hand side of the photo.
Ascidiacea (commonly known as the ascidians or sea squirts) is a class in the Tunicata subphylum of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" made of the polysaccharide tunicin, as compared to other tunicates which are less rigid.