Trochidae
The Trochidae, common name top-snails or top-shells, are a taxonomic family of very small to large sea snails, marine gastropod molluscs in the clade Vetigastropoda (according to the taxonomy of the Gastropoda by Bouchet & Rocroi from 2005). This family is commonly known as the "top-snails" because in many species the shell resembles a toy spinning top. 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 and the second osphradium 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. Description. 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 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 sculptured. The internal shell is nacreous. They have a brown, entirely corneous, circular, multispiral operculum which fits the aperture 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 peristome is generally not continuous. These shells are often brightly colored and adorned with darker bands. The Trochidae differ from the Turbinidae in having a corneous, never calcareous, operculum, which is always multispiral. Habitat. 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. Distribution. 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. Ecology. Life cycle. The Trochidae are dioecious, and the fertilization 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. Taxonomy. 2005 taxonomy. This family consists of six following subfamilies (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005): 2008 taxonomy. The family Trochidae was redefined according to Williams et al. (2008). The tribes from Trochinae were raised to subfamilies, Margaritinae was moved to the family Turbinidae, and Halistylinae provisionally stays in Trochidae. 2010 taxonomy. Williams et al. (2010) added three new subfamilies to Trochidae : Alcyninae, Fossarininae and Chrysostomatinae. The subfamily Lirulariinae is now incorporated within the subfamily Umboniinae. In this study was also shown that the subfamily Margaritinae is not monophyletic. Here is also shown, which  genera were placed into these three new subfamilies: Genera. Genera within the family Trochidae include: Umboniinae - synonyms: Lirulariinae, tribe Bankiviini, tribe Isandini, tribe Talopiini and tribe Umboniini. Main characteristics: eyes pedunculate; left tentacle attached to a frontal appendage; mantle reflected over the edge of the aperture; radula: six lateral teeth on each side; the shel is polished; the peristome is incomplete; the umbilicus is generally closed by a callosity Other genera within the family Trochidae include: