Solution

Buccal diverticulum is a short and thick-walled projection which extend forwards through the proboscis stalk into the proboscis coelom. This is a hollow tube like projection. This is a tubular outgrowth from the mouth cavity forward into the proboscis.The wall is composed of a single layer of tall and vacuolated endodermal cell. Hemichordata is known as half chordate because of the buccal diverticulum. The structure resembles like a rudimentary notochord present in the dorsal or back side and supporting axis for primitive vertebrates.
Thus, the correct answer is option A.