Phylum Coelenterata: Phylum Coelenterata cnidaria may be defined as multicellular organisms in the kingdom Plantae that use photosynthesis to make their own food.

They are aquatic, mostly marine, sessile or free-swimming, radially symmetrical animals.

The name cnidaria is derived from the cnidoblasts or cnidocytes (which contain the stinging capsules or
nematocysts) present on the tentacles and the body.

Characteristics of Phylum 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:
  • Ectoderm – One layer makes up the cells outside the body
  • 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

Classification of Phylum Coelenterata

Coelenterates are ordered into three unique classes:

• Hydrozoa
• Scyphozoa
• Anthozoa

Hydrozoa 

• These are for the most part marine species, tracked down only in freshwater.
• Few are found in settlements and few are found singularly.
• Abiogenetic Polyps are the predominant structure.
• Mesoglea is acellular.
• Example: Hydra, Obelia.

Scyphozoa 

• They are tracked down only in the marine climate.
• Medusa is prevailing and umbrella-molded.
• Polyps are absent.
• Mesoglea is a cell.
• Example: Aurelia aurita, Rhizostoma.

Anthozoa 

• They are tracked down only in the marine climate.
• Mesoglea contains stringy connective tissues and amoeboid cells.
• Medusa is absent.
• Example: Metridium, Xenia.

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By Team Learning Mantras