Answer to Question #223939 in Zoology for Debbie

Question

Write notes accompanying each of the Porifera specimens about cell types, skeletal parts 

and canal system. (not a paragraph more than 5 lines) 

Answer 1

Sponges are classified within four classes: calcareous sponges (Calcarea), glass sponges (Hexactinellida), demosponges (Demospongiae), and the recently-recognized, encrusting sponges (Homoscleromorpha). The presence and composition of spicules and spongin are the differentiating characteristics between the classes of sponges. Demosponges, which contain spongin and may or may not have spicules, constitute about 90% of all known sponge species, including all freshwater ones, and have the widest range of habitats. Calcareous sponges, which have calcium carbonate spicules and, in some species, calcium carbonate exoskeletons, are restricted to relatively shallow marine waters where production of calcium carbonate is easiest. They contain no spongin.