The shell is small, rudimentary, auriform (ear-shaped) and is situated far back on the animal. The shell is incapable of containing the body, and is reduced to the function of a shield for the lungs and heart.
The shell is a minimal, primitive, and auricular (ear-shaped) appendage situated far back on the animal. Its primary function is to provide protection for vital organs like lungs and heart, rather than enclosing the body.