Classification of Porifera

 The phylum porifera has been subdivided into three classes based primarily on the nature of the skeleton. 

The three classes are as follows-

CLASS 1. CALCAREA

This classes comprises calcareous sponges as their skeleton on spicules are made up of calcium carbonate. (L.calcarius=limy, Gr., sponges=sponge) 

Characters

1. Members of these class are similar in size extending up to 15 cm in length and may be solitary or colonial.

2. The body shape is usually cylindrical or vase-like. 

3. The osculum is narrow, terminal and fringed with bristles. 

4. The skeleton consists of separate calcareous spicules which may be monaxon, triradiate or tetraradiate. 

5. The collar cells are comparatively of larger size. 

6. The canal system is sycon, ascon, or leucon type. 

7. The colour of the body is white or dull brown. 

8. The exclusively marine and occur in shallow coastal water. 

Class Calcarea is divided into two order -

Order 1. Homocoela

1. The body is small, cylindrical and thin walled without internal folds. 

2. The canal system is simple or ascon type. 

3. Spongocoel is lined throughout by choanocytes or collar cells. 

Example- Leucosolenia

Order 2. Heterocoela

1. The body is comparatively bigger, vase-like and thick walled with internal folds. 

2. The canal system is sycon and leucon type. 

3. Only the flagellated chambers are lined by choanocytes cells. 

Example- Grantia, Sycon(scypha) 

CLASS 2. HEXACTINELLIDA

This class comprises glass sponges having triaxon or hexactinial spicules made up of silica. (Gr., hexa=six, action=rays or tri=3, sponges=sponge) 

Characters

1. The members are moderate size, extending up to 1m in length and are usually solitary. 

2. The body shape is usually cylindrical cup-shaped or funnel shaped. 

3. The osculum is wide and usually covered over by the silicieous seel. 

4. The skeleton consists of triaxon as hexactinial silicieous spicules often fused resembling spun glass. 

5. Dermal epithelium is present. 

6. The canal system is simple Rhagon type. 

7. The choanocytes cells are restricted to the finger like flagellated chamber. 

8. The are exclusively marine and occur chiefly in tropical deep sea water. 

Class Hexactinellida is divided into 2 older -

Order 1. Hexasterophora

1. The beautiful glass like body is cylindrical, very light and attached to the substratum directly. 

2. The spicules are hexasters having star-like appearance. 

3. The flagellated chambers are radially and regularly arranged. 

Example- Euplectella(Venus' flower basket) 

Order 2. Amphidiscophora

1. The body usually rounded oval and attached to the substratum by the root tufts. 

2. The spicules are amphidiscs that is with a convex disc, bearing a crown of backwardly directed marginal teeth at both ends. 

3. The flagellated chambers are irregularly arranged. 

Example- Hyalonema(glassrope sponge). 

CLASS 3. DEMOSPONGIAE

This class comprises diverse and complicated sponges with skeleton fibres or a combination of both or totally absent. (Gr., demos=frame, sponges=sponge). 

Characters

1. Members of this class are highly organised varying from small to large size and may be solitary or colonial. 

2. The body shape is variable being rounded, oval, cup-like, funnel like or cushion like

3. The skeleton is composed off silicieous spicules or spongin fibres or a combination of both or none. 

4. The silicieous spicules are monaxon or tetraxon. 

5. The canal system is complicated or leucon type. 

6. The choanocytes cells are restricted to small and rounded flagellated chambers. 

7. The body is generally compact and brightly coloured. 

8. They are mostly marine but few are freshwater and occur in shallow water as well as deep water. 

Class Demospongiae are divided into three subclasses-

Subclass 1. Tetractinellida

1. The body is rounded or flattened with dull to brightly occuring in shallow water. 

2. Siliceous spicules, if present, are tetraxon and sometime totally absent. 

3. Spongin fibres are absent. 

Subclass Tetractinellida is divided into 3 orders- 

Order 1. Myxospongida

1. The body surface is velvet like and the structure is simple. 

2. The spicules is lacking or absent. 

Example - Oscarella

Order 2. Carnosa

1. The structure is homogeneous. 

2. Equal-sized spicules are present. 

Example- Chondrilla

Order 3. Choristidia

1. The body form is usually elaborate. 

2. Both small and large size spicules are present. 

Example- Geodia, Ancorina

Subclass 2. Monaxonida

1. The body form is variable occuring in shallow as well as deep water. 

2. The skeleton consists of monaxon spicules distinguished into mega scleres only. 

3. Spongin fibre may or may not be present. 

Subclass Monaxonida is divided into 4 orders- 

Order 1. Hadromerina

1. Mega scleres are mostly tylostyle. i.e. the broad and is knobbed. 

2. Micro scleres are usually absent and if present are star-like. 

3. Spongin fibres are absent. 

Example - Cliona (boring sponge) 

Order 2. Halichondrina

1. Mega scleres are always more than one kind. 

2. Micro scleres are usually absent. 

3. Spongin fibres are present but they are very scanty. 

Example- Halichondria (crumb of bread sponge) 

Order 3. Poecilosclerina

1. Mega scleres are of two or more kinds and United by spongin fibres into regular network. 

2. Micro scleres maybe curved, bow-shaped or C-shaped. 

Example- Microciona

Order 4. Haplosclerina

1. Mega scleres are always diactinal and and pointed at both end. 

2. Micro scleres are may or may not be present.

3. Spongin fibres bare usually present.

Example- Chalina(mermaid's gloves),Spongilla (freshwater spones). 

Subclass - Kerotosa

1. The body is usually rounded and massive with a leathery surface and dark colour occuring generally warm shallow water. 

2. The skeleton exclusively composed of spongin fibres. 

3. The spicules are totally absent. 

Example- Euspongia (bath sponge), Hippospongia (horse sponge).