68 



A CLASSIFICATION OF THE PHYLUM PORIFERA. 



Class CALCAREA (Sponges with 

 spioules of lime). 



Order Homoccela (the 

 internal cavity lined 

 throughout with Choa- 

 nocytes Ascon type.) 



Order Heterocoela (Choa- 

 nocytes restricted to 

 chambers of internal 

 cavity Sycon type). 



, Leucosolenia. 

 Clathrina. 



Example, Sycon (Grantia). 



Class HEXAOTINELLID^J: 

 (Sponges with a skeletal 

 framework of siliceous spi- 

 oules). 



Examples, Euplectella 

 basket). 



(Venus Flower- 



Hyalonema (Glass-rope Sponge). 



Class DEMOSPONGIJC (Sponges 

 without spicules, or with a 

 skeleton of siliceous spicules 

 combined with horny spongin 

 in flexible fibrous cords). 



Examples, Euspongia (the Bath sponge of 

 commerce). Has an elastic 

 skeleton of spongin only. 



Spongilla (the 

 Sponge). 



freshwater 



Halichondria (Crumb-of-bread 

 Sponge). A common encrust- 

 ing Sponge of the sea-shore. 



Cliona (a boring Sponge). 

 Halisaroa (without spicules)^ 



