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Phylum Porifera

Definition- They evolved from colonial protozoans and thus they are more complex than the protozoans. They are pore bearing animals.

They include about 10,000 living and fossil species and 1,400 genera.

Phylum Porifera General Characters

1. Habit and habitat: Aquatic, sedentary, mostly marine but fresh water also.

2. Body: Diploblastic and non-cellular mesenchyma layer is present in between two layers. Loosely arranged cells with tissue grade system.

3. Shape: Variable plant like.

4. Symmetry: Radial (mostly) or asymmetrical.

5. Surface bears numerous minute' pores known as ostia. These are openings of canal system. One large opening osculum forming the blind sac body plan.

6. Cellular organisation: Interior lining is made of cells or choanocytes.

7. Canal system: Water current in the body is maintained by the canal system.

8. Mouth: Absent.

9. Digestion: Intracellular. These are biofilters.

10. Skeleiton : Internal and is made otspicules and spongin fibres. These spicules are chemically made up of silicon, calcium and spongin fibres and are proteinaceous in nature.

11. Sensation: Localised.

12. Locomotion: Absent.

13. Greatest power of regeneration.

14. Sex: Hermaphrodite or unisexual.

15. Reproduction: Asexual by buds and regeneration and sexual by gametes.

16. Fertilization: Internal cleavage holoblastic.

17. Development: Indirect with ciliated larva. Two types amphiblastula larva and parenchymula larva.

Classification-

Class 1-Calcarea or Calcispongiae

1. Habit and habitat: All marine and simple in structure.

2. Skeleton: Spicules of calcium carbonate. e.g. leucosolenia, grantia, scypha, sycon etc.

Class 2-Hexactinellida or Hyalospongiae

1. Habit: Mostly deep sea.

2. Skeleton : Triaxon (or 6 rayed) spicules separate or fused.

e.g. euplectella, hyalonema.

Class 3-Demospongiae

1. Habit: Mostly marine but includes fresh water species also.

2. Skeleton: Silicious spicules or of spongin fibres or of both or absent.

e.g. cliona, spongilla etc.

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