PHYLUM CTENOPHORA (Or. kteno, comb + phoros, to hear)
Animals in the phylum Ctenophora are called sea wnalnuts or comb jellies. This phylum has 90 described species. These all species are marine. Most ctenphorans has a spherical form. But several groups are flattened or elongated. Phylum Ctenophora have following characteristics:
- They are diploblastic.
- They have tissue-level organization.
- They have biradial symmetry.
- Gelatinous mcsoglea is present bk..mcen the epidermis and yastrodermis.
- Castrovaseular cavity is present
- Nervous system in the form 01 a nerve net
- They possess adhesive structures called colloblasts.
- They have eight rows or ciliary bands called comb rows. They are used for locomotion.
Phylum ctenophora has two classes:
1. Class Tentaculata: Their bodies contain tentacle,. These tentacles may be covered with sheath. Tentacles can be retracted in this sheath. Example: Pleurobrachia:
2.Class Nuda: They are without tentacle. Uodv is Flattened. They have highly branched gastrovascular cavity. Example Beroe
It has a spherical or 0void, transparent body. Its body is about 2 cm in diameter. It occurs in the cold waters of the Atlantic and Pacific Oceans.
1. Comb rows: Pleurobranchia has eight meridional (vertical) hands cilia. I These cilia are called comb rows. Comb rinks are present between the oral and aboral poles. Comb rows are locomotory structures. They are coordinated by a statocvst. Statocvsts are at the aboral pole. Pleurobranchia normally swims with its aboral pole present downward. The statocyst detects tilting. The comb rows adjust the animal’s position.
2.Tentacles: It has two long branched tentacles. These tentacles arise from pouches near the aboral pole. Tentacles capture prey . Tentacles possess contractile fibers. These fiblers retract the tentacles, and adhesive cells colloblasts.
3. Nutrition: The tentacles capture and transfer the prey into mouth. The mouth opensin to a branched gastrovascular canal system. Some canals are blind. But two small canals open to the outside near the apical sense organ. Thus ctenophores have an anal opening. Anal opening is absent in cnidarians. Some undigested wastes are eliminated through these canals. Some wastes are also eliminated through the mouth.
4. Reproduction: Pleurobranchia is monoecious. Two bands like gonads are associated with the gastrodermis. One of these is an ovary and the other is a testis. Gametes are shed through the mouth. Fertilization is external. A slightlyflattened larva develops.