Phylum Porifera: General characteristics and Classification

May 29, 2017 Gaurab Karki Class 11, Zoology 0




General characteristics of Phylum Porifera

  1. Kingdom: Animalia
  2. Habitat: Aquatic, mostly marine, few are terrestrial
  3. Habit: They are solitary or colonial.
  4. Grade of organization: cellular grade of body
  5. Shape: Body shape is variable, mostly cylinder shaped
  6. Symmetry: Asymmetrical or radially symmetrical.
  7. Germ layer: Diploblastic animals. The adult body wall contains two layers, outer dermal layer and inner gastral layer. In between these two layers, there is a gelatinous and non-cellular mesoglea containing numerous free amoeboid cells.
  8. Coelom: Absent; acoelomate but spongocoel is present
  9. Surface of the body has numerous perforation called ostia (for the entry of water) and a large pore at the apex called osculum (for the exit of water).
  10. Water canal system present
  11. Endoskeleton: Either calcareous spicules (calcium carbonate) or siliceous spicules (silica) or sponging fibers (protein).
  12. Nutrition: holozoic
  13. Digestion: Intracellular
  14. Nervous system: absent
  15. Circulatory system: absent
  16. Reproduction: Asexual: by budding or gemmule or regeneration; Sexual: gamatic fusion
  17. Fertilization: Internal

Classification of Phylum Porifera

Based on the type of skeleton system the phylum Porifera is divided into three classes

  • Class 1: Calcarea or Calcispongiae
  • Class 2: Hexactinellida or Hyalospongiae.
  • Class 3: Demospongiae

Class 1: Calcarea or Calcispongiae

(calcarius: lime / calcium))

  • Habitat: Exclusively marine
  • Habit: Solitary or colonial nature.
  • Endoskeleton: calcareous spicules composed of calcium carbonate
  • Symmetry: Radially symmetry
  • Shape: Cylindrical shape
  • Examples: Sycon, Leucosolenia

Class 2: Hexactinellida or hyalospongiae:

(Hex: six, actin: ray, idea: terminal)

  • Habitat: Exclusively marine (deep sea)
  • Habit: Solitary in nature.
  • Endoskeleton: six- rayed siliceous spicules.
  • Symmetry: Radially symmetry
  • Shape: Cylindrical shape.
  • Examples: Euplectella, Hyalonemma

Class 3: Demospongiae

(Demos: frame)

  • Habitat: Mostly marine and some are freshwater
  • Endoskeleton: Siliceous spicules or sponging fibres or both or none
  • The spicules are monaxon or tetraxon but never six-rayed
  • Symmetry: asymmetrical.
  • Shape: Irregular
  • Canal system complicated.
  • Spongocoeal is totally absent.
  • Examples:  Spongilla.

Phylum Porifera: General characteristics and Classification