True coelom develops as a split in

The above diagram shows the germ layers. The animals having structures shown in the figures $A$ and $B$ are respectively called:

Statement $X$: The body of the animal is divided into identical radial parts from the central axis.
Reason $Y$: Animals possess bilateral symmetry.

Give a scientific reason: Sessile animals are common in aquatic habitats.

Animals in which the body cavity is absent are known as?

Animals are classified on the basis of which of the following features?
$I$. Coelomic cavity
$II$. Level of organisation
$III$. Notochord
$IV$. Skeletal structure