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Marine benthos and plankton at all latitudes. Considered ancestral to all chordates, having as larvae both a notocord and hollow nerve cord. Small marine invertebrates attached as adults to various substrates, and motile as larvae, propelled by a tail lost during ontogeny. Some species are capable of slow movement along the substrate by detaching and reattaching. Others remain pelagic as adults, moving with a hydrojet after loss of their tail. An excellent description of tunicate larval anatomy using TEM images (Katz 1983) confirms earlier contentions (Kowalevsky 1866) that the body plans of the tunicate tadpole and vertebrate larvae or homologues. Prior to Kowalevsky the tunicates had been named by Lamarck (1809) who considered them to be shell-less mollusks. Most species are marine. Most tunicates are hermaphroditic but apparently minimize self-fertilization. The gelatinous planktonic forms are indisciminant filter feeders on small particles (as small as 0.1 μm) using a variety of mucoid structures, outcompeting copepods in this fraction of food size by two to three orders of magnitude. Some can double their mass within a day, and reach sexual maturity in as little as two days (50 hours), then produce hundreds of eggs. Some have “streamlined” life cycles, eliminating the larval stage altogether (Alldredge and Madin 1982). At least one species, Oikopleura dioica, is bioluminescent (Galt 1978) likely housing luminous bacteria (Nealson and Hastings 1979) as their "house" can emit light whether occupied or not. Information on nonindigenous species can be found online.
References:
Alldredge, A.L., and L.P. Madin 1982. Pelagic tunicates: Unique herbivores in the marine plankton. BioScience 32:655-663. Galt, C.P. 1978. Bioluminescence: Dual mechanism in a planktonic tunicate produces brilliant surface display. Science 200(4337):70-72. Katz, M.J. 1983. comparative anatomy of the tunicate tadpole, Ciona intestinalis. Biol. Bull. 164:1-27. online Kowalevsky, A. 1866. Entwickelungsgeschictte de einfachen ascidien. Mem. L’Acad. Imperiale Sci. St. Petersbourg 10:1-19. Lamarck, J.B. 1809. Zoological Philosophy (trans., H. Elliot), reprinted in 1963. Hafner, NY. Nealson, K.H., and J.W. Hastings 1979. Bacteial bioluminescence: Its control and ecological significance. Microbiol. Rev. 43:496-518.