Why remove the encrusting animals at all? The plants and animals that bore,
drill, gnaw, and encrust shells form a rich community, especially in the
warmer parts of the ocean. They can include algae, foraminifera, sponges,
corals, polychaete worms, bryozoans, bivalves, gastropods, echinoids, and
many others. A shell may show the marks of healing after unsuccessful
attempts at predation, breakage or drillholes from successful predation,
abrasion from being dragged by a hermit crab, encrustation by other animals
using the shell as a mini-hardground, borings by sponges or clams using the
shell as a safe haven, and so on. Battered shells have a history. Perfect
shells are beautiful, but lack character.
 
On a more serious note, we paleoecologists leave the encrustations on the
shells because we want to know all about ancient communities of living
organisms, not just one component.
 
Andrew K. Rindsberg
Geological Survey of Alabama