30 



T. F. GOREAU AND W. D. HARTMAN 



The clionids secrete a skeleton of siliceous spicules of three types: 

 tylostyles, oxeas, and spirasters (Fig. 9). Tylostyles are present in 

 all species; to these may be added oxeas or spirasters or both. The 

 size and shape of the spicules as well as the configurations of the 



Fig. 9. Siliceous spicules of Cliona vastifica Hancock. A, tylostyles; B, 

 smooth or spined oxeas; C, spirasters. (From Hartman, 1958.) 



excavations provide the most readily used characters for classifying 

 these sponges. 



In Cliona most of the cells of the sponge lie in galleries excavated 

 within calcareous matter. But the incurrent pores and excurrent 

 oscules must maintain contact with the external medium. Typically 

 these openings are localized on papillae which protrude from holes 

 excavated to the surface of the calcareous matter (Fig. 1). Numer- 



