The Trochidae, common name top-snails or top-shells, are a

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

of various sized sea snails, marine gastropod molluscs in the subclass

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 Bouchet ...

. 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 ...

Taxonomy

The family Trochidae consists of the following subfamilies: * Alcyninae Williams, Donald, Spencer & Nakano, 2010 * Cantharidinae Gray, 1857 * Carinotrochinae S.-Q. Zhang, J. Zhang & S.-P. Zhang, 2020 * Chrysostomatinae Williams, Donald, Spencer & Nakano, 2010 * Fossarininae 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 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'' Thiele, 1924 * †'' Coeloconulus'' Nützel, 2012 * '' Enida'' 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 ...

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 whorls. 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 ...

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.marinespecies ...

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; blo ...

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 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 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, 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 herbivores, grazing with their radulae on rocky surfaces, feeding on algae and vegetable detritus, 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