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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



widely separated places within it. In contrast to 

 what is the case with the ascidians of the cold 

 regions of the world, the ascidians of this area are 

 generally found numerous in the shallow waters 

 along the shores and in depths of not more than 

 5 to 20 fathoms and only rather exceptionally in 

 more than 50 fathoms. In fact, only one species 

 that can be called a really deep-water species 

 {Pyura antillarum, obtained near the Lesser 

 Antilles in 496 fathoms) is known from the West 

 Indian region. 



Leaving out of consideration a few uncertain 

 forms and a few that are probably better re- 

 garded as merely subspecies, only about 81 

 apparently valid species of ascidians are known 

 from the West Indian region, in the broad sense 

 of that term explained above, which includes all 

 the tropical and semitropical waters of the eastern 

 or Atlantic side of the American continent. Of 

 these, 64 are compound ascidians; the remaining 

 17 are simple ascidians. 



It is remarkable that no less than 71 of these 

 species have already been foimd in the Gulf of 

 Mexico; 3 of them and 1 additional form as yet 

 undescribed have not been found anywhere else, 

 though future collecting will probably show their 

 distribution to be wider. It is very evident that 

 it is the shallow region that borders the eastern 

 side of the Gulf along the west coast of Florida, 

 and particularly the southern end of it, that has 

 the richest ascidian fauna. Unquestionably, the 

 maintenance, for many years, of the Marine Lab- 

 oratory of the Carnegie Institution on the Dry 

 Tortugas and the consequent, exceptionally thor- 

 ough collecting that has been done in that vi- 

 cinity has contributed much to give us a better 

 knowledge of its fauna, yet that region, with its 

 many shoals and coral reefs, its numerous small 

 islands, and the cm-rents that converge toward 

 the Florida Straits to form the Gulf Stream, 

 provides particularly favorable conditions for 

 such animals as the ascidians; an environment 

 better than we have yet found anywhere else in 

 that region of the world. 



In the northern part of the Gulf, ascidians are 

 less numerous in species, though they may be 

 abundant in individuals, except where the water 

 is of reduced salinity near the mouths of rivers, a 

 condition to which most ascidians are very sensi- 

 tive. There are two northern species (Molgida 

 manhattensis and Bostrichohranchus pUvlaris), well- 



known on the coasts of the Middle States, that 

 occur on the Louisiana coast but have not been 

 found in southern Florida. Possibly this inter- 

 rupted distribution may be due to the compara- 

 tively recent elevation of southern Florida above 

 the sea level. 



There are still long stretches of the coasts of the 

 Gulf, including most of the Texan and Mexican 

 parts, that have been very little or not at all in- 

 vestigated, though we can scarcely expect that 

 much that is new will be found there. No ascidians 

 have been recorded from the deep, central part of 

 the Gulf. 



Among the commoner and conspicuous ascidians 

 of the Gulf are: Compound ascidians: Amarou- 

 cium stellatum, A. constellatum, Polyclinum con- 

 stellatum, Didemnum candidum, Eudistoma cap- 

 sulatum, E. tarponense, Clavelina picta, C. gi- 

 gantea, Distaplia hermvdensis, Perophora viridis, 

 Ecteinascidia turbinata, Botryllus schlosseri, B. 

 planus, Botrylloides nigrum. Simple ascidians: 

 Ascidia nigra, A. interrupta, Polycarpa obtecta, 

 Styela partita, S. plicata, Pyura vittata, Micro- 

 cosmus exasperatus, Molgula occidentalis. For 

 descriptions and illustrations see Van Name 

 1930, 1945. 



None of the ascidians or other tunicates of the 

 Gulf appear to have any economic importance, 

 though when small and young they furnish some 

 food for crabs, fishes, and other animals, but the 

 larger ascidians, whether simple or compound, do 

 not seem to be attractive to such predators, 

 owing chiefly to the toughness or unpalatability 

 of the test which forms so much of the bulk of the 

 body or to its lack of enough food value to make it 

 worth eating. None of the Gulf species are used 

 as an article of human diet as a few large species 

 are in some foreign countries. Neither are they 

 known to be harmful, though they sometimes are 

 a component of the growth that fouls the bottoms 

 of vessels, but rarely to any important extent. 



THE PELAGIC TUNICATA 



These require only brief mention in the present 

 work. Those of one class (Larvacea) are too small 

 to attract notice. One of them (Oikopleura 

 tortugensis) was described from and reported 

 abundant near the Dry Tortugas (Brooks and 

 Kellner 1908). 



Those of the other class (Thaliacea) are larger 

 and much better known, especially the salpas 



