''Halistylus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of very small

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 ...

mollusk Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The ...

s in the

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 ...

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 top snails.

Description

The small, polychromatic shell has a cylindrical shape. It is holostomatous, i.e. the

aperture In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...

is rounded or entire, uninterrupted by the

siphonal canal The siphonal canal is an anatomical feature of the shells of certain groups of sea snails within the clade Neogastropoda. Some sea marine gastropods have a soft tubular anterior extension of the mantle called a siphon through which water i ...

, notch, or by any other extension. The operculum is multispiral and coriaceous. There is no spiral

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 ...

. Such a cylindrical shape is rather uncommon in the family

. But the belonging of this genus to this family is certified by the shell structure, the pearly aperture and anatomical features. Dall, W.H. (1890) Scientific results of explorations by the U.S. Fish Commission Steamer Albatross. No. VII – Preliminary report on the collection of Mollusca and Brachiopoda obtained in 1887–88. Proceedings of the United States National Museum, 12, 219–362, pls. 5–14
/ref> This genus was previously considered a subgenus of the genus '' Cantharidus'' Montfort

Species

Species within the genus ''Halistylus'' include: * '' Halistylus columna'' (Dall, 1890) * '' Halistylus genecoani'' McLean, 1984 * '' Halistylus pupoideus'' (Carpenter, 1864) ;Species brought into synonymy: * ''Halistylus circumstriatus'' Pilsbry, H.A., 1897: synonym of '' Halistylus columna'' (Dall, 1890) * ''Halistylus pupoides'': synonym of ''Halistylus pupoideus'' (Carpenter, 1864)

References

{{Taxonbar, from=Q3137580 Trochidae Gastropod genera