Phlebobranchia and Stolidobranchia

Along with Aplousobranchia, Phlebobranchia and Stolidobranchia comprise the three orders of ascidian. These two groups consist mostly of solitary ascidians, although some stolidobranch species form colonies. The solitary stolidobranch species are much more likely to have a leathery, opaque test, often covered in epiphytes, while phlebobranchs usually have a smoother and more transparent test.