PHYLUM CHORDATA 



227 



particles and passes them on to the stomach and intestine. 

 The anus opens near the exhalent aperture inside the tunic. 

 Many species of sea-squirts are colonial and form masses 

 known to fishermen as "sea pork" (&, ti). 



Some tunicates are not attached but swim at the surface 

 of the ocean. The salpas, for example (Fig. 90, c, d) are 



FIG. 90. Simple Chordates. The sub-phyla represented are as follows: 

 a-d, g, h, Tunicata; e, Cephalochorda ; /, Enteropneusta. The separate figures 

 are: a, tunicate tadpoles; 6, Leptoclinum, or "sea pork," a colonial tunicate; 

 c, a chain Salpa ; d, Salpa, a swimming tunicate ; e, amphioxus ; /, Dolichoglossus ; 

 g, Molgula, a typical "sea squirt;" h, Amarcecium, a colonial tunicate. 



beautifully transparent, barrel-shaped animals ^which swim 

 by drawing water into the front of the tunic^and forcing 

 it out behind. They occur singly or in chain-like colonies. 

 The Larvacea are another group of free-swimming tunicates 

 which resemble minute tadpoles in their general form. 



Most adult tunicates have the chorda greatly reduced 

 or absent, but all of them develop from little tadpoles in 



