Coelenterata

Phylum Coelenterata is a group of aquatic, or marine organisms and a member of the Animal kingdom. They are usually found attached to the rocks at the bottom of the sea. These are the multicellular and simplest group of invertebrate animals, found in colonies or solitarily.

Characteristics of Coelenterata

• These are mostly aquatic or marine habitat animals.
• These species exhibit a tissue-level organization.
• The mouth is enclosed by thin and short tentacles.
• They are diploblastic animals, in which, the body is made up of two layers of cells:

1. Ectoderm – One layer makes up the cells outside the body
2. Endoderm – the other forms the inner lining of the body.

• 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.
• They excrete and respire through simple diffusion.
• The mode of reproduction is asexual, which is through budding.
• The sexual mode of reproduction is seen only in a few Coelenterates.

E.g., Hydra, Rhizostoma, Xenia, etc.

Also Refer: Budding

Classification of Coelenterata

Coelenterates are classified into three different classes:

• Anthozoa
• Hydrozoa
• Scyphozoa

Hydrozoa

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

E.g., Hydra, Obelia

Scyphozoa

• They are found exclusively in the marine environment.
• Medusa is dominant and umbrella-shaped.
• Polyps are not present.
• Mesogloea is cellular.

E.g., Aurelia aurita, Rhizostoma.

Anthozoa

• They are found exclusively in the marine environment.
• Mesogloea contains fibrous connective tissues and amoeboid cells.
• Medusa is not present.

E.g., Metridium, Xenia.

Learn more in detail about Phylum Coelenterata, its structure, functions and other related topics at BYJU’S Biology.

Also check: Physalia: Classification, Characteristics and Life Cycle

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