THE INVERTEBRATE LEGIONS 



131 



Tunicates: Class Tunicata — Figure 44 



The sea squirts are the most common prochordates and are most hkely to be 

 encountered. They are Httle, round, or elongate, vaselike animals that have two 

 openings, an incurrent opening for taking in water, and an excurrent one for 

 passing water out. Thus, they resemble clams in this respect and filter-feed 

 exactly as clams do. Ciona and Molgula are two common, shallow-water sea 

 squirts that live attached in groups to rocks or pilings in shallow water. The 

 name "sea squirt" is derived from the habit that these animals have of squirting 

 water when they are handled. 



There are several almost transparent members of this class that might be 

 mistaken for comb jellyfish. Like comb jellyfish, they are pelagic and swarm 

 on the open sea. Some of them are solitary and others are colonial and all are 

 filter feeders. Salpa is one solitary form of fairly large size. Pyrosoma lives in the 

 tropics, is colonial, and has living in it a luminescent bacteria. Large masses 

 of Pyrosoma, when stimulated, emit light strong enough to read by. Young 

 (1950) reports that this light may be a protective device since fishes that seize 

 these animals drop them when their lights go on. 



Avv\pVi ioxuS-2 in. 



<nolc)u.lci-1 in. 



C \ ov-\aL- o >r> 



Fig. 44. Prochordates. Drawn from life. 



SALPIO 



