THE 



TUNICATA 



OF 



THE AUSTRALIAN MUSEUM. 



TUNICATA. 



The Tunicata (or Urochorda) are hermaphrodite marine 

 chordate animals which show in their development the 

 essential vertebrate characters, but in which the notochord 

 is restricted to the posterior part of the body, and is in most 

 cases present only during the free -swimming larval stages. 

 The adult animals are usually sessile and degenerate, and 

 may be either solitary or colonies, fixed or free. The nervous 

 system is in the larva of the elongated, tubular, dorsal 

 vertebrate type, but in most cases degenerates in the adult 

 to form a small ganglion placed above the pharynx. The 

 body is completely covered with a thick cuticular test 

 ("tunic") which contains a substance similar to cellulose. 

 The alimentary canal has a greatly enlarged respiratory 

 phatynx (the branchial sac) which is perforated by two or 

 many more or less modified gill slits, opening into a peri- 



