CLASSIFICATION OF PHYLUM PORIFERA
Phylum porifera is classified mainly basing on skeleton . It is divided into 3 classes. sponges spicules plays a very important role in classification of porifera.
1. Class: Calcarea
2. Class: Hexactinellida
3. Class: Demospongiae
CLASS 1 : CALCAREA
1.Skeleton is made by calcareaous spicules.
2.They show single spongocoel cavity which opens to the outside through a single opening called osculum.
3.Radially symmetrical animals.
4.Choanocyte cells are large.
This is divided into 2 orders.
Order 1 : Homocoela:
1.Spongocoel is lined by choanocytes internally.
2.Simple sponges or included in this order.
Ex : Clathrina, Leucosolenia, Olynthus.
Order 2 : Heterocoela
1.Spongocoel is lined by epithelial cells.
2.Choanocytes restricted to radial canals only.
3Leuconoid or Syconoid canal system is seen. Ex : Sycon. Grantia.
CLASS II : HEXACTINELLIDA (OR) HYALOSPONGIAE :
1. Skeleton contains six rayed, or triaxon, siliceous spicules.
2. Radially symmetrical.
3. These are also known as glass sponges.
This class includes 2 orders
Order 1. Hexasterophora :
1. The spicules are of hexasters type.
2. They are attached to hard objects. Ex : Euplectella
Order 2. Amphidiscophora :
1. The spicules are amphidiscs.
2. These sponges are attached to the substratum by root tufts.
Ex : Hyalonema -Glass rope sponge
CLASS III : DEMOSPONGIAE :
1.Skeleton either absent or present. The skeleton contains spongin fibres or silicious spicules or both.
This class is divided into 3 subclasses.
Subclass 1. Tetractinellida :
1.The skeleton consists of tetraxon spicules or without spicules.
2.They are mostly solid rounded structures.
3.Leuconoid canal system is present. This subclass is divided into three orders.
Order 1. Myxospongida :
1.Structure is simple
2.Skeleton is absent. Eg.Oscarella
Order 2. Carnosa (or) Homosclerophora :
1)Equal sized spicules are present.
2)Megascleres and microscleres are not sharply differentiated.
Ex : Plakina.
Order 3. Choristida :
I) Microscleres and megascleres are distinct.
Subclass 2. Monaxonida :
1) Skeleton consists of monaxon spicules.
2)Spongin fibres may or may not be present.
3) They are cosmopolitan in their distribution.
4)Shallow or deep water forms. This subclass includes 3 orders.
Order 1. Hadromerida :
Spongin fibres absent.Monaxon spicules are represented by tylostyles.
Eg : 1) Cliona (Boring sponge) 2)Tethya.
Order 2. Halichondrida
Monaxon spicules are seen.
Eg : Halichondria.
Order 3. Poecilosclerida :
Monaxon spicules are present. Microscleres are sigmas, toxas etc.
Eg : Microciona.