Write the general characters of the phylum porifera.

Explanation

(i) These pore bearing animals are commonly called sponges. They are aquatic, mostly marine, asymmetrical and a few species live in freshwaters.
(ii) They are primitive, multicellular, sessile animals with cellular level of organisation in which the cells are loosely arranged. They are either radially symmetrical or asymmetrical animals.
(iii) They possess a water transport system or canal system where water enters through minute pores called ostia lining the body wall through which the water enters into a central cavity (spongocoel) and goes out through the osculum.
(iv) This water transport system is helpful in food gathering, circulation, respiration and removal of waste.
(v) Choanocytes or collar cells are special flagellated cells lining the spongocoel and the canals.
(vi) Nutrition is holozoic and intracellular. (vii) All sponges are hermaphrodites.
(viii) They also reproduce asexually by fragmentation or gemmule formation and sexually by the formation of gametes.
(ix) Development is indirect with different types of larval stages such as parenchymula and amphiblastula.
(x) eg. Sycon (Scypha), Spongilla (fresh water sponge). 19. Write about the canal system found in Porifera.