Question

How many openings does the digestive system of a cnidarian have?

Answer 1

Hint: Cnidarians belong to phylum cnidaria of animal kingdom. They are diploblastic animals having radial or biradial symmetry. They are mostly marine and swimming. They have an extracellular form of digestion and common opening for ingestion and egestion.

Complete answer:
Cnidarians involve jelly fishes, hydra, corals etc. They belong to the phylum ‘cnidaria’. Normally food is ingested or taken up by mouth and ejected or excreted through anus because higher species of animal kingdom have two openings. However, Cnidarians have extracellular digestion and the gastrointestinal cavity has only one single opening which serves as the mouth and anus for them.
They have stinging cells called ‘nematocysts’ for killing their prey as well as capturing their prey. Ingestion and egestion takes place through one common opening. Therefore they have incomplete digestion. For e.g. jellyfishes
Although they do not have a well-developed buccal cavity for proper mastication of food but their mouth area functions in the same way. Since they are primitive organisms they don’t have a well-developed circulatory, digestive and excretory system.
They exchange gases and absorb nutrition by diffusion between the cells. The nutrient is taken up and absorbed by each and every cell by simple diffusion. Since they need diffusion for exchange of gases and nutrients therefore they are diploblastic and also they have a mesoglea layer which facilitates the exchange of nutrients and gases.

Note: Cnidarians are primitive forms of organisms in the animal kingdom. Since they have a simple organ system they mainly thrive in marine environments which helps them survive better and facilitates the process of digestion, excretion and circulation.
Since they do not have a well-developed organ system they are diploblastic having only epidermis and gastrodermis and have a mesoglea layer to facilitate exchange of gases and nutrients.