The animals had canteen-shaped body armor and had large branchial plates that extended out and curved downward in a triangular shape, very similar to those of the pycnosteids.

An element of the median oral plates (that would correspond to the lower lip or chin in gnathostomes) extends out in a long rod-shaped appendage, called the "pseudorostrum."

In the type species, D. nathorsti, the lateral edges of the branchial plates and of the pseudorostrum are serrated.

Water flows ejected by their gill openings may worked to stabilize and control lateral movements.

However, burrowing theory has problems, because gill openings are placed on the lower part of body, risking suffocation.