Phylum Cnidaria/Coelenterata: General Characteristic and Classification




General characteristics of Phylum Coelenterata

  1. Kingdom: Animalia
  2. Habitat: aquatic, mostly marine.
  3. Habit: solitary or colonial. Each individual is known as zooid.
  4. Symmetry: radially symmetrical
  5. Grade of organization: tissue grade of organization.
  6. Germ layer: diploblastic, outer ectoderm and inner endoderm. Mesogloea separates these two layer
  7. The body has a single opening called hypostome urrounded by sensor y tentacles.
  8. Coelom: gastrovascular cavity or coelenteron.
  9. Nematocyst: organ for capturing and paralyzing pray, present in tentacles
  10. Nutrition: holozoic
  11. Digestion is both intracellular and extracellular.
  12. Respiration and excretion are accomplished by simple diffusion.
  13. Circulatory system: absent
  14. Nervous system: poorly develop
  15. Many forms exhibit polymorphism ie. Polyp and medusa
  16. Polyps are sessile, asexual stage
  17. Medusa are free swimming, sexual stage
  18. Metagenesis: asexual polypoid generation alternate with sexual medusoid generation
  19. Reproduction: Asexual: by budding; Sexual: by gamatic fusion
  20. Fertilization: internal or external
  21. Development: indirect with larval stage
  22. (Koilos: hollow, enteron: cavity)

Classification of Phylum Cnidaria/Coelenterata

The phylum coelenterate is divided into three classes on the basis of development of zooids:

  • Class1: Hydrozoa
  • Class2: Scyphozoan or Scyphomedusae
  • Class3: Anthozoa or Actinozoa

 Class1: Hydrozoa

(Hydra; water; zoon: animal)

  • Habitat: mostly marine, few are fresh water
  • Habit: some are solitary and some are colonial
  • Asexual Polyps is dominant form
  • Medusa possess true velum
  • Mesogloea is simple and acellular
  • Examples: Hydra, Obelia, Physalia physalis (portuguese man of war), Tubularia

Class 2: Scyphozoa or Scyphomedusae

  • Habitat: exclusively marine
  • Habit: solitary, freely swimming
  • Medusa is dominant and it is Large bell or umbrella shaped.
  • Polyps is short lived or absent
  • Mesogloea is usually cellular
  • Examples: Aurelia aurita (Jelly fishe), Rhizostoma

Class 3: Anthozoa or Actinozoa

(Anthos: flower; zoios: animal “flower like animals”)

  • Habitat: exclusively marine
  • Habit: Solitary or colonial
  • Medusa stage is absent
  • Mesogloea contains fibrous connective tissue and amoeboid cells.
  • Examples: Metridium (sea anemone), Telesto, Tubipora, Xenia

Phylum Cnidaria/Coelenterata: General Characteristic and Classification