(63) 



CLASS TUNICATA. 



ANIMAL acephalous, soft, or coriaceous, simple or 

 compound, without shelly covering or hard parts, 

 having two envelopes or tunics and two apertures, an 

 inhalent and an exhalent. Outer tunic or test varying 

 in form in the different families, from a simple sac in 

 the solitary or social to a common gelatinous envelope 

 in the compound species. Liner tunic or mantle always 

 soft and sac-shaped. Branchiae forming a large internal 

 cavity more or less reticulated. Circulation alternately 

 reversed at short intervals in opposite directions. Her- 

 maphrodite. 



Order 1. SACCOBRANCHIATA. 



Animal usually sessile and generally attached, more 

 or. less sac-shaped, simple or compound. Bra-ncliise 

 forming, an internal reticulated sac. Undergoing a 

 metamorphosis, the young in its first or larval state 

 being tadpole-shaped and swimming freely through 

 the water by means of a long vibratile tail. 



Tribe 1. SOLITAELffl. 



(Simple and Social Ascidians.) 



ls single or united into groups at the base, 

 sac-shaped or occasionally elongated, with two tunics, 

 the outer (test) coriaceous .or membranous, the inner 

 (mantle) soft and muscular, enclosing the viscera. 

 Two tubular or papillose apertures (the branchial or 

 inhalent and the anal or exhalent), usually not far 

 apart, never at opposite ends. Branchial sac generally 

 occupying a large part of the interior of the body. 

 Branchial orifice with a circle of tentacular, tubercular 

 filaments. 



