Porifera and Its Features

Porifera

Porifera Phylum

Sponges are animals of the phylum Porifera (means "pore bearer"). They are multicellular organisms which have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells. Sponges have unspecialized cells that can transform into other types and which often migrate between the main cell layers and the mesohyl in the process. Sponges do not have nervous, digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes. 

  

Classes  

Sponges were traditionally distributed in three classes: calcareous sponges (Calcarea), glass sponges (Hexactinellida) and demosponges (Demospongiae).However, studies have shown that the Homoscleromorpha, a group thought to belong to the Demospongiae, is actually phylogenetically well separated. Therefore, they have recently been recognized as the fourth class of sponges 

Calcarea :Its features
Cell structure :Single nucleus, single external membrane. 

Spicules: calcite may be individual or large masses, 

Spongin fibers : never
Massive exoskeleton: made of calcite if present,  

Body form:asconoid, syconoid, leuconoid or solenoid. 

Glass sponges : Its features 

Cell structure :Mostly syncytia in all species 

Spicules: SilicaMay be individual or fused 

Spongin fibers : never  

Massive exoskeleton: never
Body form: leuconoid . 

Demosponges :- Its features

Cell structure :Single nucleus, single external membrane 

Spicules: Silica 

Spongin fibers : never In many species 

Massive exoskeleton: In some species.Made of aragonite if present. 

Body form: leuconoid . 

Homoscleromorpha: Its features

Cell structure :Single nucleus, single external membrane 

Spicules: Silica 

Spongin fibers : never In many species 

Massive exoskeleton: Never
Body form: Sylleibid or leuconoid