The word Cnidaria is formed by combining the Greek word knide meaning thorn and the Latin word area. Nidarians are called flower of the sea. The former name of the order Nidaria is Cilenterata. The marine animal Chironex fleckeri is the world’s most poisonous jellyfish (it can kill 67 people). Animals of this phase form colonies under the sea like a tropical rain forest. They form reefs or reefs. The number of species in this category is about 10,203. Cnidaria was named by scientist Leuckart (1847).
Characteristics of Cnidaria
1. They are diploblastic animals. That is, their cells have two cell layers called ectoderm and endoderm.
2. Between the ectoderm and endoderm is an acellular layer called mesoglia.
3. Their body shape is filamentous, tubular and umbellate.
4. The body consists of nidoblast cells, which bear nematocysts.
5. There is a body cavity called gastrovascular or cilantern. The cilianteron is called the alimentary canal. It acts as the mouth and anus and participates in digestion and transport.
6. Cellular and organelle division of labor is seen.
7. The life cycle includes genetics, metagenesis and polymorphism.
8. In the life cycle there are stationary polyp dasa and active medusa dasa.
9. Body does not have organ system, respiratory system and circulatory system. The nervous system is underdeveloped.
10. They are multicellular, asymmetrical and headless.
11. Food material is digested extracellularly and intracellularly.
12. Respiration occurs through ciliated planula larvae.
13. Twenty species of Nidaria are freshwater. The remaining Nidaria are marine.
Characteristics Key words to remember: diploblastic, mesoglia, nidoblast, coelenteron, division of labor, metagenesis, polymorphism, polyp, medusa]
Classification of Cnidaria
The order Cnidaria is divided into 4 classes.
1. Hydrozoa: They live in water. Polyp or medusa stages are seen in the life cycle. Mesoglia are cellless. Genitalia arise from ectoderm. Like- Hydra viridis, Obelia geniculata.
2. Scyphozoa: These are cup or bell or umbrella shaped animals. Medusa Dasha is the main one in the life cycle. Genitalia arise from endoderm. Mesoglia are large and composed of cells and fibers. For example, Aurelia aurita
3. Cubozoa: They are storm-like creatures. Their Medusa Dasa is the main one. For example, Metridium
4. Anthozoa: They are flower-shaped organisms. A polyp stage is present in the life cycle. Mesoglia are composed of fibrous connective tissue. Genitalia arise from endoderm. For example, Metridium senil, Gorgoni verrucosa.
Some animals of Cnidaria
Hydra – Hydra vulgaris
Chlorohydra – Chlorohydra viridissima
Jellyfish – Aurelia aurita
Portuguese Man of War – Physalia physalis
Adamsia – Adamsia palliata
Obelia- Obelia geniculata
Sea fan – Gorgonia ventilina
Sea feather – Pennatula aculeata
Sea saffron – Metridium senile
Carydea- Carybdea alata
Cyanea – Cyanea capillata
Chironex – Chironex fleckeri
Brain Coral – Meandrina meandrites
Gorgonia- Gorgonia verrucosa
Red Coral – Corallium rubrum
Kamangola jelly – Stomolophus meleagris
Jelly fish
Jellyfish are marine animals belonging to the order Nidaria. It consists of a hanging part called manubrium. There are four oral arms with shafts. Numerous hollow cores exist. For example – Aurelia aurita.