Phylum Ctenophora Definition, Classification, Characteristics, examples

Definition of Phylum Ctenophora

Ctenophores, which are transparent, jelly-like and free-swimming marine animals, have biradial symmetry, comb shaped ciliary plates for locomotion, and lasso cells. However, nematocytes are lacking. They are also called comb jellies or sea walnuts.

Characteristics of Phylum Ctenophora

  • They are marine, solitary, and free-swimming pelagic animals. There was no evidence of polymorphism or attached stages.
  • The body can be transparent, gelatinous or pear-shaped.
  • They are biradially symmetrical and have an oral-aboral alignment.
  • The external surface has 8 ciliary plates that are comb-like for locomotion. They are also known as comb jellies.
  • They are equipped with a pair long, solid, retractile tentacles.
  • Their body organization is cell-tissue quality.
  • Their bodies are acoelomate, “diploblastic”, and have ectoderm as well as endoderm. The body wall is composed of an outer epidermis and inner gastrodermis. It also contains a middle jelly-like mesoglea, scattered cells, and muscle fibres. Ctenophora can also be called “triploblastic”.
  • Their digestive systems include the mouth, stomodaeum complex gastrovascular canals and 2 aboral anal pores.
  • They are devoid of nematocysts.
  • They are equipped with special sensory and adhesive cells, i.e. Coloblasts and lasso cells are found in tentacles, which aid in food capture.
  • They lack the skeletal, circulatory and respiratory organs.
  • Their nervous system is of diffused types, and their aboral end bears an organ called statocyst.
  • They are monoecious, hermaphrodite; gonads can be found on the walls of digestive canals.
  • They develop directly with the characteristic cydippid larva.
  • They are unable to reproduce sexually and do not have the ability to produce multiple generations.
  • They are also known for their regeneration and paedogenesis.

Classification of Phylum Ctenophora 

Ctenophora Phylum contains approximately 100 species, and is divided into 2 classes


Class 1. Tentaculata

  • Adults with two long aboral tentacles.
  • Some larvae have tentacles while others have oral lobes.
  • The mouth is narrower than the pharynx.

Order 1. Cydippida

  • Simple, round, or oval body.
  • Blindly, the digestive canals close; there are no anal pores.
  • Tentacles have two long, branched branches.
  • Tentacles can be retracted into pouches and sheaths.
  • Examples: Mertensia, Pleurobrachia, Hormiphora

Order 2. Lobata

  • The body is oval and laterally compressed.
  • Adults have large, slender, flap-like auricles around their mouths.
  • The larva has sheath or pouched tentacles.
  • Tentacles with and without sheath for adults are reduced.
  • The ring at the oral ends connects the gastrovascular canals.
  • Examples: Mnemiopsis, Bolinopsis

Order 3. Cestida

  • The body is elongated, compressed, or flat, and ribbon-like.
  • There are two main tentacles within the sheath, but they are smaller.
  • There are many small tentacles that run along the oral edge.
  • Combs plates in 4 rows, but rudimentary.
  • Examples: Cestum, Velamen

Order 4. Platyctenea

  • The oral-aboral axis is very compressive and flattens the body.
  • 2 well-developed tentacles with sheath.
  • Adults get fewer comb plates
  • This is how it works for creeping.
  • Examples: Ctenoplana and Coeloplana

Order 5. Thalassocalycida

  • They can be found in surface waters as low as 2,765 Ms in the Atlantic Ocean and the Mediterranean Sea.
  • The body may have a bell-shaped shape and can be up to 15cm in diameter.
  • A central cone-shaped peduncle holds the mouth open.
  • The peduncle is flanked by a pair of small tentacles.
  • Com jelly is a transparent, colorless substance. It is usually difficult to see.
  • The bell is held wide open by the prey to capture it. Zooplankton.
  • Presumably, shemaphroditic.
  • This species is not as able to swim as other comb jellies.
  • Examples: Thalassocalyce Inconstans.

Class 2. Nudu

  • Large, conical body with compressed laterals.
  • Without oral lobes or tentacles.
  • Large pharynx and wide mouth
  • Voracious feeder.

Order 1. Beroida

  • There are no oral lobes or tentacles.
  • Large, conical and laterally compressed body.
  • Large mouth.
  • Voluminous Stomach
  • Examples: Beroe

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