Rhaphischismatidae 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
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 ...
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 ...
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 in the superorder
Vetigastropoda
Vetigastropoda is a major taxonomic group of sea snails, marine gastropod mollusks that form a very ancient lineage. Taxonomically the Vetigastropoda are sometimes treated as an order, although they are treated as an unranked clade in Bouch ...
.
Vetigastropoda Paleodb
/ref> They date from the Lower Carboniferous
The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
(Mississippian). The family contains a single genus, ''Raphischisma''. In the Bouchet & Rocroi, 2005), this family is assigned to 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 usu ...
.[Treatise on Invertebrate Paleontology Part I, R.C. Moore (ed) Geol Soc of America and Univ. Kansas Press, 1960.
]
Genera
''Raphischisma''[ is the only known genus. Its description is that of the family.
]
Description
''Rhaphycasma'' is characterized by a discoidal shell with a rounded periphery, depressed spire
A spire is a tall, slender, pointed structure on top of a roof of a building or tower, especially at the summit of church steeples. A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spire ...
, umbilical callus formed by the inward extension of the lower aperture lip, and a deep, narrow slit, that extends along the upper surface, near the upper suture. The unique features of the lower 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 ...
generate an umbilical callus and deep, long, exhalent slit on the upper side along with the generally smooth form. These shell characters set this genus, and family, apart from other gastropods in the same superfamily.
References
Gastropod families
{{paleo-gastropod-stub