The correct answer is Shells of Mollusca. Explanation & Key Takeaways: Conchology • Conchology is the study of mollusc shells. Conchology is one aspect of malacology, the study of molluscs; • however, malacology is the study of molluscs as whole organisms, whereas conchology is confined to the study of their shells. • It includes the study of land and freshwater mollusc shells as well as seashells and extends to the study of a gastropod's operculum. • Conchology is now sometimes seen as an archaic study, because relying on only one aspect of an organism's morphology can be misleading. • However, a shell often gives at least some insight into molluscan taxonomy, and historically the shell was often the only part of exotic species that was available for study. • Even in current museum collections it is common for the dry material to greatly exceed the amount of material that is preserved whole in alcohol. • Conchologists mainly deal with four molluscan orders: the gastropods, bivalves, Polyplacophora and Scaphopoda. • Cephalopods only have small internal shells, with the exception of the Nautiloidea. • Some groups, such as the sea slug nudibranchs, have lost their shells altogether, while in others it has been replaced by a protein support structure.