This is a Tunicate species which begins its life in a gelatinous "house" it secretes around itself. Water is taken in, filtered and then moved on to another set of filters, and eventually thw filtered water with only the smallest of plankton is consumed. After the "house" stage the larvae turns into a small tadpole-like stage and is mobile. The photos above are of the adult stage.
See Barnes in Taxonomic References for further information.