264 



SYSTEMATIC ZOOLOGY 



SUBTYPE II. TUNICATA 



The Tunicata (Lat. tunica, mantle), sometimes called the 



Urochorda (Gr. oupd, tail, and x°P^V, cord), are all marine 



animals of wide distribution. They vary 

 from a few millimeters to ten or fifteen 

 centimeters in 

 length, and a 

 few are bril- 

 liantly colored. 

 Some are at- 

 tached through- 

 out their adult 

 life and are 

 known popular- 

 ly as sea squirts 

 or scientifically 

 as ascidians 

 (Gr. aa/ciSiov, 

 bag); others 

 are free-swim- 

 ming and for 

 the most part 

 pelagic, i.e. near 



the surface of the ocean ; they are 



generally very transparent like the 



jellyfishes. In both the attached 



and the free-swimming Tunicata 



some genera consist of simple 



individuals, each living singly 



by itself, while others are com 



pound, several or many individ- 

 uals being associated in a colony. 

 The group derives its name 



from the outer covering of the 



body, which consists of a test or < 



/ and Sedgwick s Text-book.) 



tunic, largely a secreted structure 



composed of a substance resembling vegetable cellulose, 



containing some stellate cells and a few blood vessels. 



FlG. 274. Ascidia. Ex- 

 ternal view from right 

 side ; the branchial 

 opening at the tip, the 

 atrial on the side. ( After 

 Herdman, from Parker 

 and Haswell's Manual.) 



r'li;. 275. Clavellina kp.idiformis.soxnz- 

 what diagrammatic. A, atrial orexhalant 

 pore; Af, anus; Br, gills; End, endostyle ; 

 G, brain ; (/"/), germ-gland ; Gg, genital 

 duct; Kl, atrium ; MD, stomach ;0, mouth; 



but 



It 



