PORIFERA. 



Cells not differentiated to form definite organs. Water 

 admitted through surface pores and ejected through an osculum 

 or through oscula. 



CLASS 1. Calcarea. 



With a skeleton composed of calcareous spicules. 



Subclass 1. Homoccela. 



With the gastreal layer continuous so the col- 

 lar cells line the whole gastreal cavity. (Leu- 

 cosolenia.) 



Subclass 2. Heteroccela. 



Gastreal layer discontinuous. Collar cells restrict- 

 ed to the flagellated chambers. (Grantia.) 

 CLASS 2. Hexactinellida. 



With a skeleton composed of siliceous six-rayed 

 spicules. 

 Order 1. Lyssacina. 



Spicules separate or becoming united. (Euplec- 

 tella.) 

 Order 2. Dictyonina. 



Spicules united from the first into a firm frame- 

 work. (Eurete.) 

 CLASS 3. Demospongia). 



Great diversity of structure. Dominant forms 

 of today. 



Subclass 1. Tetraxonida. 



Typically with four-rayed spicules. (Corticella.) 



Subclass 2. Monaxonida. 



Simple, usually unbranched spicules. Spongin 

 frequently present. (Cliona, Suberites, Chalina, 

 Spongilla.) 



Subclass 3. Keratosa. 



Skeleton of spongin fibers. No true spicules. 

 (Euspongia, Aplysina.) 



Subclass 4. Myxospongida. 



Without skeleton. (Oscarella.) 

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