Question

Star Fish is able to crawl over substratum by means of
A. Arms
B. Spines
C. Pedicellariae
D. Tube feet

Answer 1

Hint: Starfish, also known as sea stars belong to the phylum Echinodermata and class Asteroidea. They are marine invertebrates that feed on other invertebrates. They usually have five arms but in some species, it can even go up to fifteen arms. There are one species of starfish that has over 50 arms.

Complete answer:
Let us see the different options given in the question and the functions of each of them.
The first option is the arms. Arms are the structure that bears the spines, tube feet, and pedicellariae. The arms help in gripping. The arm also bears a small eyespot that is sensitive to light.
The next option is spines. Spines are the characteristic feature of echinoderms. Echinoderms literally mean ‘spiny skinned organisms’. The spines are used for protection in starfish and are sensitive to touch. In sea urchin spines are used for locomotion but not in starfish. It also helps in traction.
The next option is pedicellariae. Pedicellariae is an organ present in starfish that aids in defense. It is an appendage that is equipped with two movable jaws that are called valves. Each of the valves is an effector and it has its own sensory receptors.
The last option is the tube feet. Tube feet are one of the most important structures present in the starfish. Starfish uses its tube feet to move along the surface underwater. They cling on to the surface using these tube feet and swing forward in a walking-like motion.

So, the right option is option D – Tube feet.

Note:
Starfish usually have two rows of tube feet equipped with suckers. These tube feet are also used to clasp to the prey as the starfish is known to feed on other invertebrates as mentioned above. They also help in the elimination of nitrogenous wastes and in the absorption of oxygen.