''Trissexodon constrictus'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of air-breathing

land snail A land snail is any of the numerous species of snail that live on land, as opposed to the sea snails and freshwater snails. ''Land snail'' is the common name for terrestrial gastropod mollusks that have shells (those without shells are known as ...

, a terrestrial

pulmonate Pulmonata or pulmonates, is an informal group (previously an order, and before that a subclass) of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group includ ...

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 ...

mollusk 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 e ...

in the family

Trissexodontidae Trissexodontidae is a family of air-breathing land snails, terrestrial pulmonate gastropod mollusks in the superfamily Helicoidea (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005). This family has no subfamilies. The famil ...

. ''Trissexodon constrictus'' is the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

of the genus ''Trissexodon''.

Distribution

This species endemic to the western

Pyrenees The Pyrenees (; es, Pirineos ; french: Pyrénées ; ca, Pirineu ; eu, Pirinioak ; oc, Pirenèus ; an, Pirineus) is a mountain range straddling the border of France and Spain. It extends nearly from its union with the Cantabrian Mountains to C ...

and the Basque Country across 29 recorded localities, being recorded in Spain (throughout the Basque Mountains) and in

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

(in the Department of Hautes Pyrénées to Department of Pyrénées-Atlantiques), (under records of the IUCN).

Description

The shell is finely and regularly ribbed. It is strongly depressed on the upper side. The lower side is rounded. The shell has 5-6

whorls 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 d ...

. The

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 ...

has a characteristic shape. The lip is reflected and forms a "U" shape when seen from above. The umbilicus is deep and covers 1/7 of the shell diameter. The width of the shell is 6–8 mm; the height of the shell is 3–4 mm.

Ecology

''Trissexodon constrictus'' is found under stones in the soil of humid and shady deciduous forests, between moss, under leaf litter and occasionally near cave openings. It has been recorded from sea level to 800 m, and exceptionally to altitudes of 1500 m.

References

This article incorporates public domain text from the reference "Species summary for ''Trissexodon constrictus''"
AnimalBase, last modified 26 September 2008, accessed 12 January 2011. * Bank, R. A.; Neubert, E. (2017). Checklist of the land and freshwater Gastropoda of Europe. Last update: July 16th, 2017 * Gittenberger, E. (1968). Zur Systematik der in die Gattung Trissexodon Pilsbry (Helicidae, Helicodontinae) gerechneten Arten. Zoologische Mededelingen. 43 (13): 166-172. Leiden. * Kerney, M.P., Cameron, R.A.D. & Jungbluth, J-H. (1983). Die Landschnecken Nord- und Mitteleuropas. Ein Bestimmungsbuch für Biologen und Naturfreunde, 384 pp., 24 plates

External links

* Tryon G. W. (1895). ''

Manual of Conchology George Washington Tryon Jr. (20 May 1838 – 5 February 1888) was an American malacologist who worked at the Academy of Natural Sciences in Philadelphia. Biography George Washington Tryon was the son of Edward K. Tryon and Adeline Savidt. ...

'' (2)3
page 121plate 24
figure 38-40. {{Commons category Trissexodontidae Gastropods described in 1836 Taxonomy articles created by Polbot