The Trochidae,

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 ...

top-snails or top-shells, are 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 various sized

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 ...

mollusc 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 esti ...

s in 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 commonly known as the top-snails because in many species the shell resembles a toy

spinning top A spinning top, or simply a top, is a toy with a squat body and a sharp point at the bottom, designed to be spun on its vertical axis, balancing on the tip due to the gyroscopic effect. Once set in motion, a top will usually wobble for a few se ...

Taxonomy

The family Trochidae consists of the following subfamilies: * Alcyninae Williams, Donald, Spencer & Nakano, 2010 *

Cantharidinae The Cantharidinae are a taxonomic subfamily of very small to large sea snails, marine gastropod molluscs in the family Trochidae, common name top snails.Bouchet, P.; Gofas, S. (2011). Cantharidinae. Accessed through: World Register of Marine Spec ...

Gray, 1857 * Carinotrochinae S.-Q. Zhang, J. Zhang & S.-P. Zhang, 2020 * Chrysostomatinae Williams, Donald, Spencer & Nakano, 2010 *

Fossarininae The Fossarininae are a taxonomic subfamily of very small to large sea snails, marine gastropod molluscs in the family Trochidae, common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, collo ...

Bandel, 2009 * Halistylinae Keen, 1958 * Kaiparathininae B. A. Marshall, 1993 *

Monodontinae The narwhal, also known as a narwhale (''Monodon monoceros''), is a medium-sized toothed whale that possesses a large "tusk" from a protruding canine tooth. It lives year-round in the Arctic waters around Greenland, Canada and Russia. It is o ...

Gray, 1857 *

Stomatellinae Stomatellinae is a subfamily of small sea snails with a brilliantly nacreous interior of the shell, marine gastropod mollusks in the family Trochidae, the top snails.Gofas, S. (2012). Stomatellinae. Accessed through: World Register of Marine Spec ...

Gray, 1840 * Trochinae Rafinesque, 1815 * Umboniinae H. Adams & A. Adams, 1854 (1840) Additionally, the following genera have not yet been placed in any subfamily: * ''

Callumbonella ''Callumbonella'' is a genus of sea snails, marine gastropod mollusks in the family Trochidae The Trochidae, common name top-snails or top-shells, are a family of various sized sea snails, marine gastropod molluscs in the subclass Vetigastrop ...

'' Thiele, 1924 * †'' Coeloconulus'' Nützel, 2012 * ''

Enida ''Enida'' is a genus of sea snails, marine gastropod mollusks in the family Trochidae, the top snails (not assigned to a subfamily). Description The shell has a depressed-conical shape. It is widely umbilicate. The convex whorls are concentrical ...

'' A. Adams, 1860 * †'' Eocalliostoma'' O. Haas, 1953 * †'' Fagnastesia'' S. N. Nielsen, Frassinetti & Bandel, 2004 * †'' Falsotectus'' Gründel, Keupp & Lang, 2017 * †'' Guidonia'' De Stefani, 1880 * †'' Lithotrochus'' Conrad, 1855 * †'' Tylotrochus'' Koken, 1896

Description

Shell

The length of an adult shell varies between 5 mm and 130 mm. There is also a wide variation in the shape of the shell. This goes from low auriform (ear-shaped) with a wide

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 ...

to the long, slender conical forms of typical top shells. The shape may also be subglobose, turbinate or helicoid. Their height may vary between 3 mm and 152 mm. The shell contains only a few

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. These have a highly variable exterior, ranging from smooth or glossy to

sculpture Sculpture is the branch of the visual arts that operates in three dimensions. Sculpture is the three-dimensional art work which is physically presented in the dimensions of height, width and depth. It is one of the plastic arts. Durable sc ...

d. The internal shell is nacreous. They have a brown, entirely corneous, circular, multispiral operculum which fits the

snugly. The operculum is formed of numerous gradually increasing whorls with a central nucleus. The aperture may be entire, tetragonal or rounded and has no reflected

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 ...

. The peristome is generally not continuous. These shells are often brightly colored and adorned with darker bands. Species of the family Trochidae differ from those in the family

Turbinidae Turbinidae, the turban snails, are a family of small to large marine gastropod molluscs in the superfamily Trochoidea.Bouchet, P. (2014). Turbinidae Rafinesque, 1815. Accessed through: World Register of Marine Species at http://www.marinespecie ...

in having a corneous, never calcareous, operculum, which is always multispiral.Tryon (1889), Manual of Conchology XI, Academy of Natural Sciences, Philadelphia
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Internal anatomy

The animal is similar in general form to the Turbinidae. The top snails are characterized by some primitive traits: a heart with two atria. They have retained only one

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood ...

and the second

osphradium The osphradium is a pigmented chemosensory epithelium patch in the mantle cavity present in six of the eight extant classes of molluscs (it is absent in the scaphopoda and monoplacophora; among cephalopoda, only the nautilus has what appears to be ...

has been lost in the course of evolution. The mantle cavity contains a single gill. Along the side of the foot are three or more pairs of sensory epipodial tentacles. The head has a short, broad rostrum. The intertentacular lobes are simple or digitated, separate or united across the front, sometimes obsolete. The jaws are developed or absent. The

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 ...

is rhipidoglossate. The rhachidian teeth are always present and well-developed. The lateral teeth generally number 5 on each side, sometimes more numerous. The marginal teeth are narrow and very numerous.

Distribution and habitat

This family has a worldwide distribution in tropical, temperate and arctic waters. Members of this family are among the most common marine snails along the rocky shores of Europe. Most species in the family live either in the

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

or in the shallow subtidal zone, but some live in deeper water. They are usually abundant on solid, suitable substrates, like rocky shores and reefs.Poutiers, J. M. (1998). Gastropods in: FAO Species Identification Guide for Fishery Purposes: The living marine resources of the Western Central Pacific Volume 1. Seaweeds, corals, bivalves and gastropods. Rome, FAO, 1998. page 399.

Ecology

Life cycle

Species of the family Trochidae are

dioecious Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...

, and the

fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...

occurs externally by the release of eggs and sperm. Top snail eggs are laid individually or in gelatinous egg masses in the water. Individuals may hatch as free-swimming planktonic larvae or juvenile crawlers with a short swimming stage.

Feeding behavior

This family of snails consists of

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

s, grazing with their

e on rocky surfaces, feeding on

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

and vegetable

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

, and more rarely by filter-feeding, as observed in the genus '' Umbonium''.

References

* Williams S.T., Donald K.M., Spencer H.G. & Nakano T. (2010) ''Molecular systematics of the marine gastropod families Trochidae and Calliostomatidae (Mollusca: Superfamily Trochoidea)''. Molecular Phylogenetics and Evolution 54:783-809

External links

Miocene Gastropods and Biostratigraphy of the Kern River Area, California; United States Geological Survey Professional Paper 642
{{Taxonbar, from=Q1285916 Trochoidea (superfamily) Taxa named by Constantine Samuel Rafinesque