General characteristics of Phylum Coelenterata
- Kingdom: Animalia
- Habitat: aquatic, mostly marine.
- Habit: solitary or colonial. Each individual is known as zooid.
- Symmetry: radially symmetrical
- Grade of organization: tissue grade of organization.
- Germ layer: diploblastic, outer ectoderm and inner endoderm. Mesogloea separates these two layer
- The body has a single opening called hypostome urrounded by sensor y tentacles.
- Coelom: gastrovascular cavity or coelenteron.
- Nematocyst: organ for capturing and paralyzing pray, present in tentacles
- Nutrition: holozoic
- Digestion is both intracellular and extracellular.
- Respiration and excretion are accomplished by simple diffusion.
- Circulatory system: absent
- Nervous system: poorly develop
- Many forms exhibit polymorphism ie. Polyp and medusa
- Polyps are sessile, asexual stage
- Medusa are free swimming, sexual stage
- Metagenesis: asexual polypoid generation alternate with sexual medusoid generation
- Reproduction: Asexual: by budding; Sexual: by gamatic fusion
- Fertilization: internal or external
- Development: indirect with larval stage
- (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