Coelenterata

Phylum Coelenterata belongs to the Animal kingdom found usually attached to the rocks at the bottom of the sea. They are multicellular and can be found in colonies or solitarily. These are the simplest group of invertebrate animals.

Coelenterata

Structure of Cnidaria – A Coelentrate

Characteristics of Coelenterata

  • These are mostly aquatic animals.
  • The mouth is surrounded by short and thin tentacles.
  • They exhibit tissue level organization.
  • They are diploblastic, i.e., the body is made up of two layers of cells- One layer makes up the cells outside the body (ectoderm), and the other forms the inner lining of the body (endoderm).
  • They have cavities in their body.
  • The body is radially symmetrical.
  • The digestion is both intracellular and extracellular.
  • The nervous system and the circulatory system is absent.
  • The excrete and respire through simple diffusion.
  • They reproduce asexually through budding. Sexual reproduction is seen in a few Coelenterates.
  • Eg., Hydra, Rhizostoma, Xenia, etc.

Classification of Coelenterata

Coelenterates are classified into three classes:

  • Hydrozoa
  • Scyphozoa
  • Anthozoa

Hydrozoa

  • These are mostly marine and freshwater species.
  • Asexual Polyps is the dominant form.
  • Few are found in colonies and few are found solitarily.
  • Mesogloea is acellular.
  • Eg., Hydra, Obelia

Scyphozoa

  • They are found exclusively in the marine environment.
  • Medusa is dominant and umbrella shaped.
  • Polyps are not present.
  • Mesogloea is cellular.
  • Eg., Aurelia aurita, Rhizostoma.

Anthozoa

  • They are exclusively marine organisms.
  • Medusa is not present.
  • Mesogloea contains fibrous connective tissues and amoeboid cells.
  • Eg., Metridium, Xenia.

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Frequently Asked Questions

What are the characteristics of Coelenterates?

The Coelenterates have an aquatic, mostly marine organisms with a radially symmetrical body. Their mouth is surrounded by sensory tentacles to capture the prey.

Why are Coelenterates called Cnidarians?

Coelenterates are called Cnidarians because they contain specialized cells called cnidoblasts. These bear stinging structures called nematocysts.

Why are coelenterates diploblastic?

Coelenterates are diploblastic because of the presence of two layers cells namely, ectoderm and endoderm.

How do Coelenterates feed?

Coelenterates use tentacles to capture the food and draw it into the opening. Their poison is so deadly that it can paralyze very large creatures.

Are Cnidarians harmful to humans?

The nematocysts of most Cnidarians are not harmful to humans because the sting does not penetrate sufficiently into their skin.

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