Published in Zoology
Monday, 17 April 2017 00:14
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
  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.
3. Leuconoid or Syconoid canal system is seen.
Ex: Sycon, Grantia.
  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
  1. Skeleton either absent or present.
  2. 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:
1. Microscleres and megascleres are distinct.
Eg. Tetilla, Geodia.
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. Cliona (Boring sponge), Tethya.
Order 2. Halichondrida:
Monaxon spicules are seen.
Eg. Halichondria.
Order 3. Poecilosclerida:
Monaxon spicules are present. Microscleres are sigmas, toxas etc.
Eg. Microciona.

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