Phylum Coelenterata (Cnidaria)

Characteristics of Phylum Coelenterata:  

1. They are mostly aquatic organisms. 

2. They are diploblastic organisms i.e. they have two distinct body layers (ectoderm and endoderm) separated by a mesogloea.

3. They exhibit tissue level of organization.

4. They are radially symmetrical. 

5. They have only one body cavity called enteron or gut (gastrovascular cavity) with only one opening, the mouth, and no anus. The mouth also serves as an anus.

6. They have tentacles surrounding the mouth. 

7. They also possess stinging cells called nematocysts, found on the tentacles, used for capturing their prey.

8. DigestionDigestion is the breakdown of large insoluble food compounds into small water-soluble components so that they can be absorbed into the blood plasma. In certain organisms, these smaller substances are absorbed... More is both intracellularexisting, occurring, located or functioning within a cell. More and extracellularsituated or occurring outside a cell or the cells of the body. More.

9. They lack nervous and circulatory systems.

10. They reproduce asexually through budding. Sexually, they are hermaphroditesA hermaphrodite is a sexually reproducing animal or flower that has both male and female reproductive organs. Hermaphroditic animals are mostly invertebrates such as worms, trematodes (flukes), snails, moss animals, slugs... More. The sexual mode of reproduction is seen only in a few Coelenterates.

11. They exhibit polymorphism i.e. they exist in two structural forms, polyp and medusa. The medusa is umbrella-shaped and motilecapable of motion. More e.g. Jellyfish, while the polyp is cylindrical and sessile e.g. Hydra and Sea-anemone.

12. The polyp and the medusa may alternate in the life cycle of some Coelenterates (Cnidarians).

13. They live in colonies (corals) as well as solitary (Sea anemones).

14. Examples of Phylum Coelenterata are Hydra, Obelia, Jellyfish, Sea anemones, and Corals.

Classification of Phylum Coelenterata:

Coelenterates are classified into three different classes:

a. Hydrozoa e.g. Hydra
b. Scyphozoa e.g. Jellyfish
c. Anthozoa e.g. Sea Anemone