PHYLUM PORIFERA. Organisms consisting of a dermal layer of flattened cells and a gastral layer of flagellate collar cells 

 (choanocytes), separated by a gelatinous mesoglcea containing generative and skeleton-secreting cells. Numerous canals 

 communicate between the gastral cavity and the exterior. 



Class i. CALCAREA. With calcareous spicules. Ex. Leucosolenia, Grantia. 



Class 2. HEXACTINELLIDA. With siliceous spicules of triaxonic (sex-radiate) type. Ex. Euplectella. 



Class 3. DEMOSPONGI.ffi. Skeleton composed either of siliceous spicules of various types (never triaxonic) or of 

 spongin, pure or combined with spicules or foreign bodies. Ex. Oscarella, Spongilla (freshwater), 

 Euspongia (bath sponge). 



