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 (shells) to greatly exceed the amount of material that is preserved whole in alcohol. Conchologists mainly deal with four molluscan orders: the gastropods (snails), bivalves (clams), Polyplacophora (chitons) and Scaphopoda (tusk shells). 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 Some groups, such as the sea slug nudibranchs, have lost their shells altogether, while in others it has been replaced by a protein support structure. Versus shell collecting The terms shell collector and conchologist can be regarded as two distinct categories. Not all shell collectors are conchologists; some are primarily concerned with the aesthetic value of shells instead of their scientific study. It is also true that not all conchologists are shell collectors; this type of research only requires access to private or institutional shell collections. There is some debate in the conchological community, with some people regarding all shell collectors (regardless of motivation) as conchologists. History Shell collecting, the precursor of conchology, dates back thousands of years. Archaeologists have sometimes uncovered Stone Age oceanic seashell necklaces in areas far from the ocean, indicating that they were traded, and shell jewellery has been found at archaeological sites around the world. During the Renaissance people began collecting natural objects of beauty for private cabinets of curiosities. Because of their attractiveness, variety, durability and ubiquity, shells frequently became a large part of such collections. Scientific interest began to develop towards the end of the 17th century, and in 1681 The Jesuit priest Filippo Bonanni published the two-volume atlas Ricreazione dell'occhio et della mente nell'osservazione delle chiocciole ("Recreation of the eye and of the mind in the observation of molluscs"), the first treatise devoted entirely