A.

Cliona

Boring sponges, such as Cliona, attach themselves to shells of oysters, clams, barnacles etc, boring them so full of holes that their contained animals are destroyed and in time, the shells are entirely broken up. Lime of these shells gets dissolved into sea water to be used over again by other animals. Sometimes, these boring sponges may prove great nuisance to oyster beds.

A.

pachytene

During pachytene stage, crossing over takes place. It is exchange of equal segments of non-sister chromatids belonging to homologous chromosomes. The chromosome pair (i.e. bivalent) consists of four chromatids and thus crossing over takes place at four stranded stage.

B.

ADH

Antidiuretic hormone (ADH) controls the tubular permeability and concentration of sodium in the extracellular fluid. It associates with the renal pressure system and then regulates the fluid volume of body through the agency of hypothalamic osmoreceptors.

A.

radial

In radial symmetry, body is divided into similar halves by more than two planes passing through one main axis. Eg. Cnidarians or coelenterates such as Hydra, sea anemone, Aurelia, Obelia) are radially symmetrical animals with cell-tissue grade of body organization.

B.

Spleen

Spleen acts as a blood bank. The sinuses of spleen acts as reservoir of blood.