Question

Which one of the following is not part of the water vascular system of starfish?
A) Stone canal
B) Madreporite
C) Circular canal and tube feet
D) Osphradium

Answer 1

Hint: It tests incoming water and other food particles. It is an olfactory organ that is found in mollusc and it is linked with the respiratory system. Starfish have no sharp demarcation between arms and the central body, and they move using tube feet rather than wriggling movements of the whole arms.

Complete Answer:
- Starfish or sea stars are star-shaped echinoderms. They belong to the class Asteroidea group of echinoderms. Echinoderm has a unique vascular water system.
- The Vascular water system opens to the exterior with the help of a sieve-like madreporite on the abdominal surface of the animal.
- The canal in which madreporite links is called a stone canal or slender duct. This canal extends to a ring canal that encircles the mouth or oesophagus. Then, the radial canal extends along the arms and short lateral canals ending in the ampulla.
- The ampulla protrudes through a pore to the exterior and is called a podium or tube feet. Osphradium is an olfactory organ that is found in certain molluscs.

The correct answer is option D. i.e., Osphradium.

Note: Sea star moves with the help of a water vascular system. Water comes into the system through the madreporite. It is circulated from the stone canal to the ring canal and into the radial canals. The radial canals carry water to the ampullae and provide suction to the tube feet. The water vascular system is a hydraulic system used by echinoderms.