Sea Squirt - Cnemidocarpa finmarkiensis (about 3 cm across)

Sea Squirt or Tunicate

One of the most fascinating invertebrate animals is known as the sea squirt, so called because they consist mainly of a bag-like body filled with water, that will sometimes squirt out if they are handled. This bag-like animal with two openinngs is covered by a relatively thick skin known as a tunic (after the tunics of ancient Rome), and thus the other commonn name, tunicate. In a way, sea squirts are like vaccuum cleaners: water containing plankton food is first sucked into the body through the incurrent opening; it then passes through an internal filtration bag made of mucous-covered mesh where the food is trapped; and then the water passes out of the body through the excurrent opening.

The life history of all tunicates exhibits a fascinating stage that is microscopic in size and lives for a time suspended in the sea as a member of the plankton -- the tadpole larva. Equipped with a long tail useful for swimming, a dorsal nervous system and an adjacent stiffening rod-like structure, the notochord, this tadpole larva has the basic characteristics that distinguish the major group of animals to which you and I belong (plus all other mammals, reptiles, birds, amphibians and fish, of course) -- the Phylum Chordata. Simply put - these bag-like animals are one of our closest invertebrate relatives. Say hello to uncle Squirt.