The Anomphalidae is an extinct

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

of fossil

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

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. These are

archaeogastropods Archaeogastropoda (also known as Aspidobranchia) was a taxonomic order of sea snails used in older classifications of gastropods, i.e. snails and slugs. Archeogastropoda are marine prosobranch gastropod mollusks, mainly herbivores, typical ...

which are included in the suborder Trochina. The Anomphalidae lived during the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

, from the Silurian to the Middle Permian. According to some authorities these snails belong instead to the Euomphalacea.

Morphologic diagnosis

Shells of the Anomphalidae are rounded, almost discoidal, low-spired trochospiral inform, possibly with a globular

body whorl The body whorl is part of the morphology of the shell in those gastropod mollusks that possess a coiled shell. The term is also sometimes used in a similar way to describe the shell of a cephalopod mollusk. In gastropods In gastropods, the b ...

. The

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An opt ...

is oval, without exhalent slit or crease. The umbilicus is narrow, open or closed. The inner shell layer is seemingly

nacre Nacre ( , ), also known as mother of pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is f ...

ous. The shell surface is generally smooth, ornamentation consisting of fine transverse lyrae or growth lines parallel to the aperture

lip The lips are the visible body part at the mouth of many animals, including humans. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be ...

.J. Brooks Knight et al 1960. Systematic Descriptions (Gastropoda), Treatise on Invertebrate Paleontology, Part I, Mollusca 1, R.C. Moore (ed). The Anomphalidae differ from the Euomphalcea to which they have been reassigned Anomphalidea in Paleobio database
/ref> in being more trochoidal, in lacking the angulation on the upper whorl surface characteristic of Euomphalacea, and in having the inner shell layer seemingly nacreous. (The inner shell layers of the Euomphalacea may be of laminar arragonite, but are never nacreous.) The Anomphalidea differ from the

Pleurotomariacea Pleurotomariacea is one of two names that are used for a taxonomic superfamily of sea snails that are an ancient lineage and are well represented in the fossil record. The name Pleurotomariacea is used by paleontologists, who, because they us ...

in lacking the often deep slit or

selenizone A selenizone (from the Greek "selene" meaning "moon", and "zone" meaning "girdle") is an anatomical structure that exists in the shells of some families of living sea snails: the slit shells, the little slit shells and the abalones, which are m ...

, which is characteristic of that taxon.

Taxonomy

J Brooks Knight, ''et al'', in the Treatise, 1960, assigned 10 genera to the Annomphalidae. They are
:'' Anomphalus'' Meek and Worthen 1866, the type genus :'' Cycloscena'' Fletcher 1958 :'' Eiselia'' Dietz'' 1911 :''

Isonema ''Isonema'' is a genus of plant in the family Apocynaceae Apocynaceae (from ''Apocynum'', Greek for "dog-away") is a family of flowering plants that includes trees, shrubs, herbs, stem succulents, and vines, commonly known as the dogbane ...

'' Meek and Worthen 1866 :'' Pycnomphalus'' Lindström 1884 :'' Turbocheilus'' Perner 1907 :'' Sosiolytes'' Gemmellaro 1889 :'' Straparella'' Fischer 1885 :'' Turbinilopsis'' de Koninck 1881 :'' Tychonia'' de Koninck 1881 At present the Anompalideae has been expanded to include 17 genera in two subfamilies established by Peel, 1984. Added to ''Anomphalus'', ''Cycloscena'', ''Eiselia'', and ''Isonema'' in the Anomphalinae are:
''Antirotiela'' Cossmann 1918, given in the Treatise as a synonym for ''Anomphalus''
:'' Frydacosta'' Cook and Nützel 2005 :'' Delphinuella'' Heidelberger 2001 :'' Givediscus'' Heidelberger 2001 :''

Littorella ''Littorella'' is a genus of two to three species of aquatic plants. Many plants live their entire lives submersed, and reproduce by stolons, but some are only underwater for part of the year, and flower when they are not underwater. Classific ...

'' Heidelberger 2001 :'' Nodinella'' Heidelberger 2001 Contained within the Pycnomphalinae in addition to ''Pycnomphalus'', ''Turbocheilus'', ''Sosiolites'', ''Strapariella'', and ''Tychonia'':
:'' Pycnotrochus'' Perner 1903 :'' Turbinilopsis'' de Koninck 1881 ''Pycnotrochus'', from the Upper Silurian of Europe, was removed from the Sinuopeidae (Pleurotomariacea); the lip has a sinus more characteristic of the original family. ''Turbinopsis'', from the Lower Devonian of North America, was removed from the Palaeotrochidae (Palaeotrochacea); has a spiral chord not found on typical Anomphalidae and an aperture with a thicker, wider lip, also atypical. Bouchet & Rocroi, 2005 simply included the Anomphalidae in "basal taxa that are certainly Gastropoda".

References

Prehistoric gastropods Prehistoric mollusc families Paleozoic molluscs Silurian first appearances Guadalupian extinctions Trochoidea (superfamily) {{paleo-gastropod-stub