Tunicates, or 'sea squirts', are members of the phylum Chordata, which also includes birds, fish, and mammals. As with other Chordates, tunicates posses a notochord during their early stages of development. Larval stages have the appearance of a tadpole, whereas the adult stage has a much more barrel-like shape. They feed by filtering sea water through a gill basket (Solomon, 2002).
Tunicate blood is particulary interesting. Unlike some blood that contains iron or copper, tunicate blood stores the rare metal vanadium, which it draws from the water (Kelly, 2003). It is still unknown how they do this (Kelly, 2003).
