Pleurotomariidae,

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...

the "slit snails", is a

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 large

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 ...

s in the superfamily

Pleurotomarioidea Pleurotomarioidea is a superfamily of small to large marine gastropods included in the order Pleurotomariida of the subclass Vetigastropoda. These are the slit shells, originally named Pleurotomariacea, in keeping with the convention for namin ...

of the subclass

Vetigastropoda Vetigastropoda is a major Taxonomy (biology), taxonomic group of sea snails, marine (ocean), marine gastropod mollusc, mollusks that form a very ancient lineage (evolution), lineage. Taxonomically the Vetigastropoda are sometimes treated as an O ...

. This family is a very ancient

lineage Lineage may refer to: Science * Lineage (anthropology), a group that can demonstrate its common descent from an apical ancestor or a direct line of descent from an ancestor * Lineage (evolution), a temporal sequence of individuals, populati ...

; there were numerous species in the geological past. The genus includes several hundred fossil forms, mostly

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 ' ...

. It is one of the oldest gastropod families, commencing in the

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

.G.W. Tryon (1890), Manual of Conchology vol. XII, p. 69
/ref> The superfamily is currently represented by a group of species that live only in deep water. This family has no subfamilies. The first living specimens of a species in this family, '' Perotrochus quoyanus'', were dredged in 1879 in deep water off the

West Indies The West Indies is a subregion of North America, surrounded by the North Atlantic Ocean and the Caribbean Sea that includes 13 independent island countries and 18 dependencies and other territories in three major archipelagos: the Greater A ...

by the "Blake" expedition of

William Healey Dall William Healey Dall (August 21, 1845 – March 27, 1927) was an American naturalist, a prominent malacologist, and one of the earliest scientific explorers of interior Alaska. He described many mollusks of the Pacific Northwest of America, and w ...

Description

The shell has a trochoidal shape. It is nacreous within. It is umbilicate or imperforate, having a deep slit or sinus in the outer superior margin of the peristome, which serves the purpose of an exhalant phase of

respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellul ...

., and leaves on the corresponding part of the

whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...

s a peculiarly sculptured band, the "anal fasciole" or the "slit fasciole." The slit is sealed up gradually behind the advancing aperture as the shells grows in size. The animal has no frontal lobes or appendages. The eyes are situated at the outer bases of the tentacles. The muzzle is as in

Trochidae The Trochidae, common name top-snails or top-shells, are a family of various sized sea snails, marine gastropod molluscs in the subclass Vetigastropoda. This family is commonly known as the top-snails because in many species the shell resembles ...

. The tentacles are long, subcylindrical and bluntly pointed. The broad epipodium (the lateral grooves between foot and mantle) is thin, entire, and fringed with a row of small, short papillae. But it does bear cirri. It is closely applied to the shell. The long

radula The radula (, ; plural radulae or radulas) is an anatomical structure used by molluscs for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food ...

has a long, narrow rhachidian tooth. It is lanceolate with its tip narrowand recurved. There are 26 laterals with the outer 5 without cusps. The inner ones are larger, with wide cusps and narrower bases. The outside of the laterals consists of 2 rows of uncini (the numerous small teeth-like or hook-like structures). The inner series number 18 and are large, strongly curved, and with scythe-shaped 1-3 denticulate cusps. The outer uncini are very numerous (40-50), small, very oblique. In '' Entemnotrochus adansonianus'' (Crosse & P. Fischer, 1861) there are considerable differences in the teeth. Some of the uncini bear little tufts of bristles at their apices. The jaws are subobsolete.

Fossil record

The Pleurotomariidae have a continuous fossil record from the Upper Cambrian onwards. After taking a considerable hit during the

Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the ...

, they have been restricted to deeper waters through the Cenozoic. In 2009, a new study in the ''

Journal of Paleontology The ''Journal of Paleontology'' is a peer-reviewed scientific journal covering the field of paleontology. It is published by the Paleontological Society. Indexing The ''Journal of Paleontology'' is indexed in: *BIOSIS Previews *Science Citatio ...

'' described the first occurrence of

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

pleurotomariids from Antarctica.

Ecology

Species in the family Pleurotomariidae live at depths of 150–300 m as

benthos Benthos (), also known as benthon, is the community of organisms that live on, in, or near the bottom of a sea, river, lake, or stream, also known as the benthic zone.mesopelagic zone The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins ...

. They are preyed upon by crustacea and fish, but are remarkably resistant to attack — they secrete a white fluid when endangered, thought to repel predators. They feed primarily on sponges, and supplement their diet with crinoids and octocorals in the wild; in aquaria, they also feed on fish and clam tissue.

Genera

Genera within the Pleurotomariidae include: * '' Bayerotrochus'' Harasewych, 2002 * '' Entemnotrochus'' Fischer, 1885 * † '' Mamoeatomaria'' Begg & Grant-Mackie, 2006Begg J. G. & Grant-Mackie J. A. (2006). "''Mamoeatomaria'', a new name for the Triassic gastropod ''Mamoea'' Begg & Grant-Mackie, 2003, pre-occupied (Mollusca: Gastropoda: Pleurotomariidae)". '' Journal of the Royal Society of New Zealand'' 36(4): 1175-8899. . * '' Mikadotrochus'' Lindholm, 1927 * † '' Obornella'' Cox, 1959 * '' Perotrochus'' Fischer, 1885 * † '' Pleurotomaria'' Sowerby, 1821 * † '' Trochotoma'' Eudes-Deslongchamps, 1842

References

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