The peramorphosis corresponds to an architectural differentiation of the species that encompasses the belt of plates bearing the internal fasciole and the anterior ambulacrum
. However, even if all the derived species of the genus are the result of peramorphic evolution, they do not follow precisely the same trend.
The "relative size" of a plate pair was defined as the area of the plate pair, divided by the area of the plate pair in ambulacrum III of the same specimen.
These findings imply that the plates in the posterior paired ambulacra (areas I and V) are the largest, that the plates in the anterior paired ambulacra (areas II and IV) are smaller, and that the plates in the anterior ambulacrum (area III) are the smallest.
Tube foot movements during burrowing involve bending away from the ambulacrum toward the sides of the arm.
Further, it is wrapped by the connective tissue and calcite ossicles of the ambulacrum and is thus prevented from expanding.