A tunicate is a member of the subphylum Tunicata of the phylum Chordate (see chordate). Tunicates are known commonly as sea squirts. They are marine and have sac-shaped bodies with two openings, a mouth and an atrial port. Water is sucked in through the mouth, filtered for food particles, and passed out through the atrial port. Many tunicates, however, have a larva that is free-swimming and exhibits all the characteristics of chordates.