Question

In starfish at the aboral end near the anus, a plate-like porous structure is found, called as
A. Skeleton plate
B. Madreporite
C. Pedicellariae
D. Tube feet

Answer 1

Hint: Starfish are echinoderms that have a calcareous opening for excretion of wastes. The aboral side refers to the opposite mouth side of the starfish. It consists of a porous structure that forms an essential part of the water vascular system.

Complete answer: The light coloured plate-like porous structure forms a calcareous opening which is called madreporite. The madreporite forms a key part of the water vascular system of starfish. It is a pressure-equalizing valve that appears red or yellow. It looks like a small wart. The central disk of all starfish and urchins consists of madreporite. The name madreporite has arrived from the fact that it looks like the Scleractinia which is a stone coral. The water vascular system of starfish consists of seawater filled tubes that help in movement, feeding, and respiration of starfish. The madreporite is the main functional unit of this system. The other parts of the water vascular system are the ring canal, the stone canal, the lateral canals, the radial canals, and the tube feet. The madreporite allows the entry of seawater into the stone canal. The stone canal is connected to the ring canal which is connected to the mouth of the starfish. The radial canals extend in the five or more arms of starfish. From radial canals, various lateral canals extend. These lateral canals then are connected to tube feet. The tube feet are a closed cylindrical structure. It has muscular walls along with suckers at the outer ends. In this way, the seawater regulates through the body of starfish.
So, the correct answer is option B.

Note: The gut of starfish consists of the disc-like structure which is extended to arms. Starfish digests the food outside its body. After digestion, the starfish takes in nutrients through seawater circulation. Nutrients get absorbed by the body tissue when it circulates through the water vascular system.