11th Class Biology Animal Kingdom Phylum-Ctenophora or Acnidaria- The comb Jellies

 (Gk. kteis = comb; pherein = To bear)

Brief History : The ctenophores as a distinct group were first recognized by Escscholtz (1829).  Hatschek (1889) placed it under a separate phylum called ctenophora.

General characters

(1) All the ctenophores are marine.

(2) They are solitary and pelagic.

(3) They are transparent.

(4) The have tissue-grade of organization.

(5) They have biradial symmetry.

(6) They are acoelomate animals.

(7) They are unsegmented.

(8) They body-wall is diploblastic.

(9) The mesogloea contains cells.

(10) Nematocysts are absent.

(11) Special adhesive cells called colloblasts are present in all ctenophores.

(12) The gastrovascular system is well developed.

(13) Two anal openings are present.

(14) Skeletal system is absent.

(15) Excretion and respiration are carried out by diffusion.

(16) The nervous system is in the form of nerve net.

(17) An aboral sense organ is present in the form of statocyst.

(18) Cilia are used for locomotion.

(19) They are hermaphrodites.

(20) Development is indirect. It includes a cydippid larva.

Classification of Ctenophora

Class 1. Tentaculata

(1) The body is simple, rounded or oval or ribbon-like.

(2) Two long aboral tentacles are present.

(3) Mouth is narrow and pharynx is small.

Examples : Pleurobrachia, Hormiphora, Mertensia Mnemiopsis, Bolinopsis, Velamen, Cestum, Ctenoplana, Coeloplana, etc.

• Cestum is commonly called “venus’s girdle”.

• Ctenoplana shows commensal with Alcyonea.

Class 2. Nuda

(1) Body is large thimble-shaped or conical.

(2) Tentacles are absent.

(3) Mouth is wide and pharynx is large.

(4) The meridional vessels are produced into a complex system of anastomosing branches.

Example : Beroe

• Befroe is commonly called “Swimming eye of cat”.