INVERTEBRATES

Phylum Porifera (Sponges)

                         Members of this phylum are commonly known as sponges.

• Habitat -

                     They are mostly marine, few are found in fresh water. 

• Body symmetry - 

                                  Mostly are assymetrical animals, no definite shape to the body.

• Level of organization - 

                                         These are primitive animals, multicellular with cellular grade of organization. 

• Motility - 

                         Adult sponges are sessile, that is they need a substratum to attach themselves to a surface and do not move.

• Mode of Nutrition - 

                                       Due to the sessile nature, sponges are filter feeders. 

• Digestion - 

                           Digestion is intracellular.

• Skeleton - 

                         The body of sponges is supported by a skeleton made of spicules or spongin fibres. 

• Reproduction -

                                Sexes are not separate, they are hermaphrodites. Hermaphroditism - condition where eggs and sperms are produced by the same individual.Sponges reproduces asexually by fragmentation and sexually by formation of gametes.

• Fertilization -

                                  Fertilization is internal.

• Development -

                                Indirect development, having a larval stage which is morphologically distinct from the adult.

• Water transport or Canal system -

                                  Sponges have water transport system. Water enters through minute pores (ostia) in the body wall into a central cavity known as spongocoel. From the spongocoel water goes out through the osculum. This water system aids in food gathering, respiratory exchange and removal of wastes.

• Choanocytes - 

                            These are collar cells, they line the spongocoel and the canals. 

• Examples: Sycon, Euspongia, Spongilla.