164 MANUAL OF NATURAL HISTOID. 



jects between the apex of the gaping valves ; 

 rudimentary branchiae developed from the 

 mantle ; shell almost equivalve. 



TUNICARIES. 



The Tunicaries comprise the " acephalous Mol- 

 lusks without shells " of Cuvier, and are the same 

 as the " Heterobranches " of Blainville. They are 

 marine animals of variable form, their bodies in- 

 vested in a thick coriaceous or gelatinous sac-like 

 mantle, with a branchial and an anal aperture, with 

 the gills differently formed, attached to the inner 

 lining membrane. They are usually fixed to rocks 

 and other sub-marine bodies, as the Ascidians and 

 Botrylli, but others among them are free and pela- 

 gian, as the Salpians and Pyrosomes. They are 

 either simple, or united together organically, form- 

 ing a compound animal of great diversity of shape 

 and complexity. In the warm seas of equinoctial 

 countries, their star-like bodies arrest the eye by 

 the richness of their tints, and the curious manner 

 in which the individuals are grouped. In their 

 young or larval state the Tunicaries are free, but 

 afterwards become fixed to one spot for the re- 

 mainder of their lives. Some species are employed 

 as food in certain parts of China and the Mediter- 

 ranean, although by no means inviting in their 

 general appearance. In the genus Chelysorna of 

 Broderip and Sowerby, the mantle is strengthened 



