General characteristics of Porifera:
(i) These are the simplest multicellular, diploblastic animals.
(ii) They are asymmetrical or radially symmetrical.
(iii) Their cells are loosely held together in a gelatinous matrix, mesoglea and do not form tissues.
(iv) Skeleton is made up of minute calcareous or silicious spicules or spongin fibre (collagen) or both.
Examples: Sycon and Spongilla.