''Gryphaea'', one of the genera known as devil's toenails, is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of extinct

oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not ...

s, marine bivalve

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

s in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Gryphaeidae The Gryphaeidae, common name the foam oysters or honeycomb oysters, are a family of marine bivalve mollusks. This family of bivalves is very well represented in the fossil record, however the number of living species is very few. All species h ...

. These

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 preserved ...

s range from the

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

period to the middle Paleogene period, but are mostly restricted to the Triassic and Jurassic. They are particularly common in many parts of

Britain Britain most often refers to: * The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands * Great Britain, the largest island in the United King ...

. These oysters lived on the sea bed in shallow waters, possibly in large colonies. The complete

s consist of two articulated valves: a larger gnarly-shaped shell (the "toenail") and a smaller, flattened shell, the "lid". The soft parts of the animal occupied the cavity between the two shells, just like modern oysters. The shells also feature prominent growth bands. The larger, curved shell sat within the mud on the sea floor. These shells are sometimes found in fossil plates along with ''

Turritella ''Turritella'' is a genus of medium-sized sea snails with an operculum, marine gastropod mollusks in the family Turritellidae.Vos, C.; Gofas, S. (2013). Turritella Lamarck, 1799. Accessed through: World Register of Marine Species at http://www.m ...

'', clams, and sometimes sharks' teeth and fossilized fish scales. Its distribution is common in areas of both Europe. A classic location to find these fossils is Redcar, on the northeast coast of England. There used to be a common folk belief that carrying one of these fossils could prevent rheumatism. The name "devil's toenail" is also used for some fossil species of the genus '' Exogyra'', which is in the same family (Gryphaeidae) as ''Gryphaea''. Two genera have been removed from this genus: ''

Pycnodonte ''Pycnodonte'' is a genus of extinct oysters, fossil marine bivalve mollusks in the family Gryphaeidae, the foam oysters or honeycomb oysters. Shells of species in this genus are found around the world in fossil shell beds from the Valanginian ...

'' and '' Texigryphaea''.

Selected species

*''

Gryphaea arcuata ''Gryphaea arcuata'' is an extinct species of foam oyster, a bivalve mollusc in the family Gryphaeidae from the Early Jurassic of Europe. It is commonly referred to in English folklore as the 'devils toenail' due to its supposed resemblance to ...

'' *'' Gryphaea dilatata''

References

External links

The Bedford Museum: ''Gryphaea''

Gryphaeidae Triassic bivalves Prehistoric bivalve genera Jurassic bivalves Cretaceous bivalves Paleocene bivalves Eocene bivalves Fossils of Great Britain Carnian genus first appearances Eocene genus extinctions Fossils of Serbia {{paleo-bivalve-stub