Hydra is an aquatic diploblastic animal. It has vase like body composed of two principal layers of cell. The cells of outer layer function as a protective and sensory epithelium also called ectoderm while those of inner layer or gastro dermis; act as a nutritive epithelium also known as endoderm.
Coelenteron
The central cavity of the body functions as a digestive cavity. The animal has one opening to the outside, which surrounded by mobile tentacles. The digestive cavity of this sort is called gastrovascular cavity or coelentron.
Nematocysts:
Embedded in the tentacles are numerous stinging cells called nematocyst. Each nematocyst consists of a hollow thread coiled within a capsule and a tiny hair like trigger projecting outside.
Ingestion
When a prey in contact with the trigger of nematocyst, the hollow thread of the nematocyst turns inside out, ejects poison and the prey is paralyzed or some times killed.
Digestion:
The glandular cells in the gastrodermis secrete proteolytic enzymes, which start extra cellular digestion. Gastrodermal flagellate cells and contraction of body cavity help in mixing food with enzymes and breaking up into fine particles. The amoeboid cells where digestion is completed intracellularly in the digestive vacuoles then engulf these fine particles.
Coelenteron
The central cavity of the body functions as a digestive cavity. The animal has one opening to the outside, which surrounded by mobile tentacles. The digestive cavity of this sort is called gastrovascular cavity or coelentron.
Nematocysts:
Embedded in the tentacles are numerous stinging cells called nematocyst. Each nematocyst consists of a hollow thread coiled within a capsule and a tiny hair like trigger projecting outside.
Ingestion
When a prey in contact with the trigger of nematocyst, the hollow thread of the nematocyst turns inside out, ejects poison and the prey is paralyzed or some times killed.
Digestion:
The glandular cells in the gastrodermis secrete proteolytic enzymes, which start extra cellular digestion. Gastrodermal flagellate cells and contraction of body cavity help in mixing food with enzymes and breaking up into fine particles. The amoeboid cells where digestion is completed intracellularly in the digestive vacuoles then engulf these fine particles.
