Assertion: Small Tiedmann’s bodies are associated with the ring ambulacral canal in the echinoderms.
Reason: Tiedmann’s bodies contain phagocytes to dispose of the bacteria.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C. Assertion is correct but Reason is incorrect.
D. Both Assertion and Reason are incorrect.

Hint:- An echinoderm is a term used for the members of the phylum Echinodermata. They are mostly marine animals. The adult echinoderms have radial symmetry. Examples of echinoderms are starfish, sea cucumbers, sea lilies, etc.

Complete Answer:-
The phylum Echinodermata is the second largest group, after chordates, including more than 7000 species. They have a wide variety of colours. Echinoderms possess a water vascular system which is a hydraulic system used for locomotion, respiration, and transport of food and water. It is composed of canals which by contraction help in the movement of the body. The water vascular system is also known as the ambulacral system.
The ring canal is present on the inner side in Echinoderms giving it an irregular shape. These structures are known as Tiedmann’s bodies. They are found as five pairs. These bodies perform an important function of producing coelomic corpuscles that dispose of the bacteria which are present in the ambulacral ring canal. So, it can be said that these bodies are associated with the ring canal and are phagocytic in nature that disposes of the bacteria. The assertion given in the question is correct and the reason given for the assertion is also accurate. So, the correct option is (A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.

Note:- Echinoderms are very important both ecologically and geologically. They can reproduce asexually and can regenerate organs and limbs. They have ossified skeletons which are used in the formation of limestone. They were also used for research purposes earlier.