Survey of the Animal Kingdom 281 



Classification of the Phylum Porifera 



Class 1 — Calcarea (kal -ka' re a) (L. calcarius, lime). — The skeleton is 

 composed of spicules of calcium carbonate (calcareous). The sponges are mostly 

 gray or white, living in shallow sea water. 



Examples: Scypha (Grantia) (Figs. 81, 82, and 87) and Leucosolenia (Figs. 

 83 and 84). 



Class 2 — Hexactinellida (hek sak ti -nel' i da) (Gr. hex, six; aktin, rays). — 

 The skeleton of these deep-sea sponges is composed of six-rayed spicules of silicon 

 (siliceous) which may in certain species be fused into a continuous skeleton re- 

 sembling spun glass. 



Example: Venus's flower basket (Fig. 85). 



OSCULUM. 



SPICULES 



BASE 



Fig. 81. — A simple sponge, Scypha (Grantia) of the class Calcarea. A young 

 bud is also shown. The entire organism is somewhat diagrammatic and enlarged. 

 (From Parker and Clarke: Introduction to Animal Biology, The C. V. Mosby Co.) 



Class 3 — Deniospongiae (de mo -spon' ji e) (Gr. demos, people; spongos, 

 sponge). — These commercial sponges usually possess skeletons of spongin fibers 

 alone or spongin fibers associated with spicules of silicon. These sponges have a 

 complicated system of canals. 



