PORIFERA 



Cells not differentiated to form definite organs. Water 

 admitted through surface pores and ejected through an os- 

 culum or through oscula. 



Class 1. Calcarea. 



With a skeleton composed of calcareous spic- 

 ules. 

 Subclass 1. Homocoela. 



With the gastric layer continuous so the col- 

 lar cells line the whole gastric cavity. (Leu- 

 cosolenia.) 

 Subclass 2. Heterocoela. 



Gastric layer discontinuous. Collar cells re- 

 stricted to the flagellated chambers. (Sycon.) 

 Class 2. Hexactinellida. 



With a skeleton composed of silicious six- 

 rayed spicules. 

 Order 1. Lyssacina. 



Spicules separate or becoming united. (Eu- 

 plectella.) 

 Order 2. Dictyonina. 



Spicules united from the first into a firm frame- 

 work. (Eurete.) 

 Class 3. Demospongiae. 



Great diversity of structure. Dominant forms 

 of today. 

 Subclass 1. Tetraxonida. 



Typically with four-rayed spicules. (Corti- 



cella.) 

 Subclass 2. Monaxonida. 



Simple, usually unbranched spicules. Spongin 



frequently present. (Cliona, Suberites, Chal- 



ina, Spongilla.) 

 Subclass 3. Keratosa. . 



Skeleton of spongin fibers. No true spicules. 



(Euspongia, Aplysina.) 

 Subclass 4. Myxospongida. 



Without skeleton. (Oscarella.) 



36 



