Phylum : Coelenterata (Cnidaria), its classification and characteristics

  • multicellular with tissue grade of body organization.
  • aquatic, mostly marine, few are found in fresh water.
  • sedentary or free swimming.
  • mostly radially symmetrical whereas few are asymmetrical.
  • diploblastic i.e. outer layer is called ectoderm and inner layer is called endoderm. There is a jelly like layer present in between these 2 layers called mesogloea.

Phylum Coelenterata (Cnidaria) Definition, Classification, Characteristics

                                                                    Image source: microbiologynotes

  • Internal hollow body cavity is present that is known as coelenteron or gastrovascular cavity.
  • blind sac body plan present. Coelenteron opens out through a mouth which helps in both ingestion and egestion.
  • mouth is surrounded by tentacles which contain stinging cells nematocytes. Tentacles help in capturing the prey, locomotion, offence and defence.
  • two types of individual are present. These are asexual polyps and sexual medusae. Some are noted for varieties of forms i.e. polymorphism.
  • nutrition is holozoic i.e. feeding on solid food particles in the manner of most animals.
  • digestion is both intracellular and extracellular.
  • primitive type of nervous system present in mesogloea in the form of nerve network.
  • respiratory, circulatory and excretory systems are absent.
  • muscular system consists of epithelio and endothelio muscle cells.
  • some of them are noted for alternation of generation (metagenesis) in between asexual polyp and sexual medusae.
  • reproduce asexually by budding and sexually by fusion of gametes.
  • development is indirect. They have free swimming planula larva.


They are divided  into three classes on the basis of presence of polyp and medusa. They are :

Class 1: Hydrozoa

  • mostly marine, few are found in fresh water.
  • solitary as well as colonial, sessile and free swimming.
  • only polyps or both polyps and medusa stage are present. But polyp stage is dominant.
  • mesogloea is simple and not cellular.
  • gonads are usually ectodermal in origin.
  • exhibit tetramerous or polymerous radial symmetry.
  • examples: Hydra, Obelia (sea fur)

Coelenterata or Cnidaria | CK-12 Foundation

                                                                                             Image source: ck12

Class 2: Scyphozoa

  • exclusively marine, solitary.
  • medusa stage is dominant, polyp stage is reduced or absent.
  • mesogloea is cellular.
  • gonads are endodermal in origin.
  • examples: Aurelia (jelly fish), Pelagia, Rhizostoma

1. Enumerate various classes of Coelenterata indicating the number into  which the phylum is divided. - Question 1, 35. Coelenterata : Characters,  Classification and Types, Invertebrate Zoology | Brainly

                                                                                         Image source: brainly

Class 3: Anthozoa

  • exclusively marine, solitary or colonial.
  • only polyp stage is present. Medusa stage is absent.
  • mesogloea is cellular.
  • body cylindrical with a bilateral or biradial symmetry.
  • gonads are endodermal in origin.
  • fertilization is external.
  • examples: Tubipora (organ pipe coral), Metridium (sea anemone), Corallium




Phylum : Coelenterata (Cnidaria), its classification and characteristics