Phylum Porifera

Porifera (Sponges) (L. porous=pore; ferre=bearer)

Porifera, or sponges, are simple, non-motile animals that live in aquatic environments. They have porous bodies and a canal system through which water flows, allowing them to filter feed on small particles.

General Characters of Phylum Porifera

1) Habitat: They are aquatic organisms generally marine, with a few freshwater species.

2) Symmetry & Shape: They have asymmetrical body. Body shape can be cylindrical, vase-like, rounded like or sac-like.

3) Germ layer: They are diploblastic animals having two layers – Pinacoderm (outer dermal layer) and Choanoderm (inner dermal layer).

4) Organisation: They are primitive multicellular animals with cellular level of organisation. They have no tissue.

5) Ostia: They have many small pores throughout the body called Ostia from where water enters to the body.

6) Osculum: A single large opening called osculum at the top of the body.

7) Spongocoel: Middle of the body has a cavity called spongocoel.

8) Choanocytes: Choanocytes or collar cells having flagella, line up the spongocoel and canals.

9) System: They have canal system for the flow of water in body.

10) Endoskeleton: Body has an endoskeleton made up of spicules composed of calcareous or siliceous spicules or spongin fibres.

11) Digestion: Digestion is intracellular and holozoic.

12) Reproduction: Asexual reproduction is seen through budding. Sexual reproduction is done by gametic fusion.

Example: Scypha sp. (Marine sponge); Spongilla sp. (Fresh water sponge); Euplectella sp. (Venous Flower Basket); Euspongia sp. (Bath sponge) etc.

Classification of Phylum of Porifera: 

1. Class Calcareous or Calcispongiae
2. Class Hexatinellida or Triaxonida or Hyalospongiae
3. Class Demonspongiae
4. Class Scelerospongiae

1. Class Calcarea or Calcispongiae 

( L. Calcis= generative of calx= lime of chalk)

1. Skeleton: Skeleton of separate spicules made up of calcium carbonate, either calcite or argonite.
2. Osculum: They have narrow osculum placed terminally provided with oscular fringe.
3. Habitat: Exclusively marine, shallow coastal water species.
4.  Shape: They have cylindrical or vase-like safe body.
5. Size: This sponges are small size about 10 cm in height.
6. Megascleres: Megascleres are monaxon, triaxon or tetraxon.
7. Canal system: Canal system is a asconoid, syconoid or leuconoid type.

Example: Leucosolenia sp. Sycon sp. (Scypha)

2. Class Hexatinellida or Triaxonida or Hyalospongiae

(G. Hex= six + aktis= ray + ell= suffix added to form diminutives)

1.  Skeleton: Skeleton of 6 ray or triaxon siliceous spicules.
2. Osculum: Spongocoel opens by wide osculum.
3. Choanocytes: Choanocytes are restricted to finger like simple or folded chambers.
4. Shape: body has cup/ vase/ urn like shape.
5. Size: Large Size sponge is about 10-30 cm in height.
6. Canal system: They have Sycon or lucon type of canal system.

Example: Euplectella sp. (Venus Flower Basket); Hyalonema sp. (Glass rope sponge) 

3. Class Demonspongiae:

(G. Demos= people + spongos= sponges)

1. Skeleton: Skeleton composed of siliceous spicules or spongin fibres both.
2. Choanocytes: Choanocytes form very small, rounded type of flagelled chambers.
3. Habitat: Mostly marine but few or freshwater.
4. Megascleres: Siliceous megasclere spicules never triaxon (6-ray)
5. Canal system: they have only Lucent type of canal system.
6. Larva: Parenchymulalarvae seen in their life cycle.
7.  Colour: Colouration in most of species for pigment granules in amoebocytes.

Example: Euspongia sp. (Bath Sponge); Spongillasp. (Fresh water Sponge)

4. Class Scelerospongiae:

1.  Skeleton: Skeleton contains spicules of both silica & spongin fibres.
2. Habitat: All are marine, exhibits crytic habitats & prefer caves.
3. Basal layer: Spicules, spongin fibres & living tissue rest on solid basal layer of calcium carbonate enclosed by chambers.
4. Canal System: They have leuconoid type of canal system.
5. Spicules:  They have small tetraxon spicules.

Example: Astrosclera sp. ; Stromatospongia sp.