Phylum Cnidaria - Practice Questions & MCQ

• This phylum consists of hydra, jellyfish, sea anemones and corals.
• These are diploblastic and radially symmetrical animals.
• They show tissue level of organization.
• These are mostly marine animals.

Body Wall and Gastrovascular Cavity of Cnidaria:

• The coelenterates show blind sac type of body plan. 
• There is a central digestive gastrovascular cavity or coelenteron with a single opening that serves as both the entry and exit for material. 
• This cavity is surrounded by the body wall that shows the following layers:
• The outer epidermis derived from the ectoderm. It consists of epitheliomuscular cells and cnidocytes. They provide covering and perform muscular contraction. 
• The inner gastrodermis derived from the endoderm. It surrounds the gastrovascular cavity. It consists of nutritive-muscular cells, gland cells and interstitial cells. Gonads are also derived from the cells of gastrodermis.
• The middle layer is non-cellular and gelatinous. It is called the mesoglea. It forms the skeleton of cnidarians.
  

Digestion in Cnidaria:

• The digestion is extracellular as well as intracellular. 
• The food is taken into the gastrovascular cavity and the enzymes are released into the cavity. They have incomplete digestive system as there is only one opening that functions as both mouth and anus.

Respiration in Cnidaria:

• The respiratory system is absent.
• The exchange of gases is facilitated through simple diffusion between cells and water.

Excretion in Cnidaria:

• The excretory system is absent. 
• The nitrogenous waste, which is mainly composed of ammonia, is removed through the process of diffusion between the cells and water.