Porifera

Porifera (Gr.Porous-Pores, ferry- bearing)

• Porifera includes plant-like creatures with a large number of minute pores. So, commonly called sponges.
• John Ellis first recognised the sponges as an animal.
• Robert Grant coined the term "Porifera".
• The study of sponges or poriferans is called parazoology.

General Characteristic feature of phylum Porifera:

• All of them are aquatic, mostly marine, rarely freshwater, solitary or colonial, sessile or redentary.
• Body shape is vase shaped, cylindrical, spherical, cup or disc-shaped. Asymmetrical or radially symmetrical.
• The cellular level of body organisation.
• Diploblastic.
• The adult body wall consists of two layers i.e. outer pinacoderm made up of a flattened cell or inner gastral choanoderm made up of complex flagellated collar cells. In between two layers, there is non-cellular mesogloea.
• In mesogloea, there is supporting endoskeleton called spicules which are made up of CaCO₃(Calcareous), SiO₃(Siliceous) or protein (SpoenginRibres).
• There is peculiar canal system whose central cavity is called paragestral cavity or sponge cell. Canal system gets in food and oxygen and carries out carbon dioxide and wastes.
• The body surface is perforated with a large number of minute inhalant pores called Ostia and one largest exhalent pore called osculum.
• Nutrition is holozoic and digestion is intracellular.
• Circulation absent, respiration, and excretion through diffusion.
• Nervous system and sense organs completely absent.
• Bisexual reproduction asexually and sexually fusion of gametes.
• Fertilization is internal.
• Develop is indirect.

Classification:

Porifera consists of almost 5000 living species. They are divided into three classes on the basis of types if spicules.

Calcarea or calerspongia:

• They are marine, solitary or colonial.
• Mononon, Trianon and tetra non-type of spicules made up of CaC0_3.
• Radially symmetrical.
• A Simple canal system.
• Eg; Sycon, Leucosolenea.

Hyatospongiea or henantinillida:

• They are marine found in deep sea and ocean.
• Trianon spicules made up of Si0₃.
• Radially symmetrical.
• Branch or unbranch canal system.
• Eg; Hyalenema, Euplectella.

Demospongiea:

• They are marine except spongilla. Spongilla is freshwater form.
• Mono and Tetracon spicules made up of spongin fibre.
• Asymmetrical
• Complex alimentary canal.
• Eg; Spongilla, Cliona.