what is abdorminal,body cavity or coelom and choanocytes?

Coelom is the specially lined body cavity where internal organs are located. Coelom is a fluid-filled cavity between the body wall and the gut and is lined by mesoderm. It is present in the body of all animals higher than the coelenterates and certain primitive worms. It is also known as body cavity or abdominal cavity.

Choanocytes are also known as collar cells. They are present in sponges. They possess a flagellum surrounded by a screen-like cellular extension. These cells line the interior of  sponges and produce a current that draws food and water into the central cavity.