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