What is Phylum Coelenterata?
- The term Coelenterata means organisms which have a hollow body structure. The phylum consists of two major subphyla namely Cnidaria and
- All the coelenterates show a tissue level of organisation. They usually have a body made up of two layers: the outer layer and the inner
- The basic structure of any coelenterate is composed of a hollow tubular structure and tentacles surrounding the single
- To study the morphology of coelenterates, they are classified into two major categories:
(i) Polyp
- Polyps are non-motile. The tube-like and cylindrical structure is attached to a support while the tentacles are placed on the upper
- The tentacles become the only structures to float around and catch hold of
For example, sea anemone. It is attached to the substratum with this basal region and has tentacles on top.
Polyp
- Medusa
- These organisms have umbrella-shaped structures and tentacles attached at the base.
- They are mostly freely floating
For example, jellyfish. The umbrella-shaped structure is composed of two layers of simple gelatinous tissue and has almost 95% water in it. Thus, most jellyfishes have a translucent appearance.
The tentacles are the most powerful tools with these organisms. They contain small cells which can be either nematocysts or colloblasts. These cells can shoot and inject toxins when sensed with danger. Thus, jellyfish stings are dangerous and painful.
Medusa Nematocysts or Colloblasts
- Coelenterates have the common basic structure of tube and tentacles. The tube has a single large opening called hypostome, which serves both functions – entry and exit of substances.
- Some coelenterates have specialised cells that secrete proteins like the Green Fluorescent Protein (GFP) which help in the phenomenon of bioluminescence.