Final answer:
In class Scaphopoda, the mantle acts as a respiratory structure forming a tube open at both ends, facilitating gas exchange for the animal.
Step-by-step explanation:
The mantle in the class Scaphopoda, which includes animals known as "tusk shells" or "tooth shells" like the genus Dentalium, plays a crucial role in their respiratory systems. These creatures, typically found buried in sand, have their mantle cavity act as a tube that is open at both ends. This opens up to the water when the anterior end is exposed, allowing for gas exchange to occur. The mantle in Scaphopoda does not contain ctenidia (gills) as seen in some other mollusks. Instead, the unique structure of the mantle cavity serves both as a respiratory apparatus and part of the feeding system in coordination with the radula and ciliated tentacles. The mantle in class Scaphopoda serves as the respiratory structure in these animals. Instead of having ctenidia like other mollusks, Scaphopods have a mantle cavity that forms a tube open at both ends. This allows oxygen to enter the mantle cavity and be taken up by the animal's tissues.