Coelenterata
Gr., koilos : Hollow; enteron : intestine
General characters
- Metazoa with tissue grade of organization
- Aquatic : mostly marines few are freshwater forms, e.g. Hydras
- Sedentary or free swimming and colonial or solitary
- Radially symmetrical except sea-anemone which is bilaterally symmetrical
- Acoelomate
- Diploblastic metazoan
- Exclusively carnivorous, no herbivorous forms known
- Exhibit polymorphism ; polyp, medusa, and blastostyle structures are formed
- Individuals are known as zooids
- Anterior end of the body has hypostome on which mouth is present surrounded by tentacles. Anus is absent.
- Possess nematocyst; serve the function of paralyzing the prey by injecting poison or to hold the prey or used for adhesion.
- Digestion is intracellular, extracellular or both
- Reproduction both sexual and asexual (budding)
- Life-cycle exhibits alternation of generation or metagenesis
3 classes based on dominance of polyp or medusa forms
| Hydrozoa (Hydros: water ; zoios : animal) | Scyphozoa (Gr., Skyphos=cup ; zoios=animal) | Anthozoa (Gr., Anthos=flower ; zoios=animal) |
| Mostly marine, some freshwater | Exclusively marine and planktonic | Exclusively marine, solitary or colonial |
| Diploblastic | Triploblastic | Triploblastic |
| Have thick mesogloea | Gastrovascular cavities have partitions called mesentries | |
| Examples: Hydra, Obelia, Physalia, Porpita etc. | Eg : Aurelia, Rhizostoma | Eg: Metridium, Alcyonium, Fungia, Heliopora etc. |
