Discuss the general characters of the phylum porifera.

Explanation

The general characters of phylum porifers are as follows:
(i) Porifers or sponges are sessile solitary or colonial with assymetrical body
(ii) Sponges develop from two germ layers. Hence, they are diploblastic animals.
(iii) They have cellular level of organization
(iv) The body wall of sponges consists of two layers-outer dermal layer or pinacoderm and inner choanocytic layer or choanoderm.
(v) The choanocytic layer consists of flagellated collar cells or choanocytes. Between these layers, there is a gelatinous material, named mesohyl or mesenchyme. It contains numerous free amoeboid cells, the amoebocytes.
(vi) The body wall encloses a large cavity, known as spongocoel. In most cases, it also contains numerous small cavities, called canals. All the cavities in sponge body are interconnected and are referred to as canal system.
(vii) Nutrition is holotrophic. Digestion is intracellular, ingestive or holozoi. Digestion occurs partly in choanocytes and partly in trophocytes.
(viii) Insponges, respiration is aerobic. Gaseous exchange occurs by diffusion of gases through the
body surfaces, which are in direct contact with water.
(ix) Excretion occurs through body surface by diffusion. Porifers are ammonotelic. Asexual reproduction in sponges occurs by fragmentation, budding, gemmules and reduction
body.
(xi) Sexual reproduction involves in the formation of ova and spermatozoa. Most of sponges are hermaphrodite. Sperms leave one sponge and enter another sponge through water current to fertilize the egg. Zygote develops into a new sponge by holoblastic segmentation.