Mogulidae, Styelidae - Tunicates (Sea Squirts, Salp)

Tunicates are groups of underwater sac-like filter feeders with an intake and an outflow siphon. They are a member of the phylum Chordata because they have the semblance of a vertebrate (called a notochord) and brain when they first develop. In their larval stages, they resemble tadpoles. Since the larvae cannot eat, they must find a place to attach to so that they develop into the round sac-like body of the adult. The brain and notochord are digested during this development. A common saying about sea squirts is that they "eat their own brain".

Tunicates may be solitary or colonial. Many will form mat-like colonies and can spread quickly, covering and smothering other organisms it encounters. This has caused some concern because of the altering of the marine habitat and their capability to smother shellfish beds and foul other hard substrates such as fishing gear, ship hulls and marine structures. Many are thought to be nonindigenous in areas where they occur, probably brought in on the hulls of passing ships.