The Anomphalidae 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 fossil

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, marine

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 ...

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

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

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

, 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 (biology), morphology of the gastropod shell, 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 ...

. The

aperture In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...

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 ...

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

lip The lips are a horizontal pair of soft appendages attached to the jaws and are the most visible part of the mouth of many animals, including humans. Mammal lips are soft, movable and serve to facilitate the ingestion of food (e.g. sucklin ...

.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 aragonite, but are never nacreous.) The Anomphalidea differ from the Pleurotomariacea 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 abalone, which are ...

, 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 Palaeotrochidae is an extinct family of fossil snails, gastropod mollusks in the clade Neritimorpha according to the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005). This is the only family in the superfamily Palaeotrochoidea. This family h ...

(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