Final answer:
The class of molluscs with a tubular shell open at both ends is Scaphopoda, known for their unique tusk-like shells, burrowing lifestyle, and modified mantle cavity used for respiration.
Step-by-step explanation:
Molluscs with a tubular shell that is open at both ends belong to the class Scaphopoda. Members of this class, also known as tusk shells or tooth shells, such as the genus Dentalium, typically have a single conical shell which is indeed open on both ends. The animals usually bury themselves in sand with the anterior opening exposed to water. They exhibit a reduced head, but possess a group of tentacles that end in ciliated bulbs, aiding in prey capture and manipulation.
Furthermore, scaphopods lack ctenidia—gill structures found in other molluscs—and instead, their mantle cavity forms a tube that opens at both ends, facilitating respiration. Their foot is similar to that seen in bivalves, which assists them in burrowing.