Question

Compare the feeding behavior of a hydra (Phylum Cnidaria) with that of a planarian (Phylum Platyhelminthes). How is their feeding behavior different?

Answer 1

Answer:

Phylum Cnidaria - are so named because of presence of stinging cells called Cnidoblast or Cnidocyte. Cnidocyte are containing staining capsule as Nematocyst. These are present on tentacles and body and are used for anchorage, defense as well as capturing prey.
Most of them are marine and few fresh water dwellers like Hydra and are Carnivores.

Diet of Hydra mainly consists of small crustaceans. They capture prey in rather passive manner, paralyzing drifting prey with stinging nematocysts, capturing with tentacles and pushing it through the open mouth aperture.
They have incomplete digestive tract (blind sac) which consists of central cavity called coelenteron with single aperture. This mouth is for ingestion as well as excretion. Digestion takes place extracellularly (in coelenteron) as well as intracellularly (in food vacuole).

Phylum Platyhelminthes - are also known as flat worms because they have dorsoventrally flattened body. Most of them are parasites but few are free living like Planaria found in salt water and fresh water bodies like rivers and pond.

Diet of Planaria includes living or dead small animals. They suck up their food through their muscular mouths. Food passes from the mouth to the pharynx which connects to gastrovascular cavity. Food is digested by lining of the gastrovascular cavity and then nutrients diffuse through to other body parts. Planaria can evert their pharynx and suck food through pharynx directly in their gastrovascular cavity.
They have incomplete digestive system with single opening, an-us is missing.