''Amastra tristis'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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 molluscs, terrestrial gastropod mollusks that have gastropod shell, shel ...

, a

terrestrial Terrestrial refers to things related to land or the planet Earth, as opposed to extraterrestrial. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on o ...

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 inclu ...

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 ...

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

in the family

Amastridae Amastridae is a Taxonomy (biology), taxonomic family (biology), family of small, air-breathing, land snails, Terrestrial animal, terrestrial pulmonate gastropod mollusks in the superfamily Pupilloidea.MolluscaBase eds. (2021). MolluscaBase. Amast ...

Description

The length of the shell can reach 18 mm, its diameter 11 mm The shell is imperforate or slightly rimate, oblong-conic, and moderately solid. The coloration transitions from blackish-purple on the initial 2–3

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). In nature File:Photograph and axial plane floral diagra ...

s to reddish-brown with a pale sutural margin, ultimately fading to light reddish-brown or nearly white on the final whorl. The last 2–3 whorls are coated with a thin, dark brown cuticle, which is often shed in angular fragments or patches and is typically absent near the aperture. The

spire A spire is a tall, slender, pointed structure on top of a roof of a building or tower, especially at the summit of church steeples. A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spire ...

is slightly convexly conic and tapers to an acute

apex The apex is the highest point of something. The word may also refer to: Arts and media Fictional entities * Apex (comics) A-Bomb Abomination Absorbing Man Abraxas Abyss Abyss is the name of two characters appearing in Ameri ...

, comprising 5½–5¾ nearly flat whorls. The first whorl is almost smooth, with the second adorned by regular radial ripples. Subsequent whorls exhibit fine growth striae, while the last two whorls display coarse growth wrinkles and fine spiral striae. The

body whorl The body whorl is part of the morphology (biology), morphology of the gastropod shell, shell in those gastropod mollusks that possess a coiled shell. The term is also sometimes used in a similar way to describe the shell of a cephalopod mollusk ...

often features several irregularly spaced spiral grooves. 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 ovate and slightly oblique, lined with a distinct internal rib within the peristome. The

columella Lucius Junius Moderatus Columella (, Arabic: ) was a prominent Roman writer on agriculture in the Roman Empire. His in twelve volumes has been completely preserved and forms an important source on Roman agriculture and ancient Roman cuisin ...

is short and moderately expanded, bearing a pronounced, spiral lamella. A thin, transparent parietal

callus A callus (: calluses) is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, b ...

subtly overlays the inner surface. The shell's axis is slender and sinuous, widening slightly with each whorl, and the lamella penetrates nearly a full whorl into the structure. The shape of the embryonic whorls and the maculation of the neanic whorls in many individuals resemble those of ''

Amastra badia ''Amastra badia'' is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusc in the family Amastridae. Description The length of the shell attains 17 mm, its diameter 12 mm. (Original description) The shell c ...

''. The incised spiral striae are also characteristic of ''

Amastra undata ''Amastra undata'' is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusc in the family Amastridae. Description The length of the shell attains 17 mm, its diameter 12 mm. (Later supplemental description ...

'', ''

Amastra transversalis ''Amastra transversalis'' is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusc in the family Amastridae. ;Subspecies: * ''Amastra transversalis bryani'' Pilsbry & C. M. Cooke, 1914 * ''Amastra transversalis transv ...

'', and others in the group to which ''A. badia'' belongs. This suggests that ''A. tristis'' represents a somewhat generalized or synthetic species within this assemblage.

Distribution

This species is endemic to Hawai, occurring on

Oahu Oahu (, , sometimes written Oahu) is the third-largest and most populated island of the Hawaiian Islands and of the U.S. state of Hawaii. The state capital, Honolulu, is on Oahu's southeast coast. The island of Oahu and the uninhabited Northwe ...

References

External links

* * {{Taxonbar, from=Q106281706 tristis Gastropods described in 1825