†Onychochilidae is an extinct

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of small,

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

, upper

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

to lower

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

s. They have hyperstrophically coiled shells which generally have smooth whorls and elongate apertures. They are commonly considered to be

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

s, i.e.

sea snail Sea snails are slow-moving marine (ocean), marine gastropod Mollusca, molluscs, usually with visible external shells, such as whelk or abalone. They share the Taxonomic classification, taxonomic class Gastropoda with slugs, which are distinguishe ...

s. The Onychochilidae is included in the Macluritacea in the Treatise, Part I, 1960, as part of the Archaeogastropoda where it is divided into two subfamilies, the Onychochilina for those with high basal spires, and the Scaevogyranae for those with low basal spires. Robert M. Linsely and William M. Kier, 1984 reassigned the Onychochilidea to the Paragastropoda, a new class of molluscs proposed for gastropod-like forms which they interpreted as being untorted - that is viscerally not twisted. The Onychochilidae was at that time placed in the Onychochilacea, a superfamily included in a new order, the Hyperstophina, named for paragastropods with hyperstrophic to depressed-orthstrophic shells. Bouchet and Rocroi, 2005 Bouchet, P. & Rocroi, J., 2005. Classification and Nomenclator of Gastropod Families Malacologia v.47. no 1-2. tentatively retained the Onychochilidae in the Gastropoda, including them along with the Clisospiridae in the superfamily Clisospiroidea, and added a third subfamily, the Hyperstropheminae, named for ''Hyperstrophema'' Horney, 1964, its sole known genus.

References

Paleobiology database classification of the subfamilies and genera
Gastropod families {{Paleo-gastropod-stub