184 



A Classification of the Sub-Phylum Tunicata. 



Order ASCIDIACEA. Fixed or free -swimming ; solitary or colonial. 

 Adults without tail and notochord. Muscles irregular. 

 Pharynx large. Numerous gill-slits opening into atrium, 

 which has one atrial aperture. Anus opens into atrium. 



Tribe 1. Ascidiae Simplices. Simple solitary Ascidians 



(the typical " sea-squirts "). Usually fixed. Tunic 



thick and opaque. Reproduction sexual (hermaphrodite). 



Generally there is a tailed larva. 



Examples, Ascidia. See description, page 182. Lives in mud 



at depths from 5 to 20 fathoms. 

 Ciona. Elongated form. Muscles form bands. 

 Digestive portion of gut is behind the pharynx. 

 A common littoral tunicate. 

 Boltenia. Body on a long stalk. 

 Styelopsis (syn. Cynthia). A common small and 



red littoral tunicate. 

 Molgula. Without a tailed larva. 



Tribe 2. Ascidiae Compositae. Compound Ascidians. Col- 

 onies usually fixed. Individuals of colony generally 

 within one common test. Reproduction asexual (bud- 

 ding or gemmation) and sexual (the embryos, developed 

 in atrium or in special atrial pouches, become tailed 

 larvae). 



Examples, Botryllus. Forms bright-coloured gelatinous in- 

 crustations on rocks and seaweed. Zooids 

 grouped in small star-like colonies, within a 

 common test ; their mouths open directly to the 

 outside, but their atrial apertures open into a 

 common chamber (the cloaca) with a central 

 outlet. 



Clavellina. Zooids grouped together on a creeping 

 stolon ; but not within a common test. A common 

 littoral tunicate ; one of the " social " forms. 



Tribe 3, Ascidiae Luciae. Free-swimming pelagic colonies, 

 shaped like hollow cylinders witli an open truncate end 

 and a closed rounded end ; the hollow being the common 

 cloaca into which open the atrial apertures of the numer- 

 ous zooids forming the cylinder wall. Tests gelatinous 

 and transparent. Phosphorescent. Reproduction asex- 

 ual (budding) and sexual. Without a tailed larva. 



Example, Pyrosoma. Colonies vary in length from a few 

 inches to about four feet. 



Order THALIACEA. Free-swimming (effected in jerks by forcing 

 water out at atrial opening). Pelagic. Solitary or 

 " sopial." Adults without tail and notophord. Musples^ 



