''Margarites rossicus'', common name : the pearly margarite, 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 ...

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

, a marine

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

Margaritidae Margaritidae is a family of small sea snails, marine gastropod mollusks in the superfamily Trochoidea (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005).Bouchet, P. (2012). Margaritidae. Accessed through: World Register ...

. There are two subspecies: * ''Margarites rossicus derjugini'' Galkin, 1955 x Bartsch MS/small> * ''Margarites rossicus rossicus'' Dall, 1919 Some authors place this species in the subgenus ''Margarites (Pupillaria)''

Description

The shell grows to a length of 32 mm, its diameter 30 mm. The large, solid shell has a trochiform shape. It has a pale gray color over a brilliant nacre. It contains 8

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). Whorls in nature File:Photograph and axial plane floral ...

s, including a small pinkish nucleus of two whorls. The spiral sculpture consists of (on 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. Spires are ...

three) strong blunt keels, of which two near the periphery are the most prominent, with subequal wide interspaces. There is a fourth less prominent one on which the suture is laid which only shows on the

body whorl The body whorl is part of the morphology of the 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. In gastropods In gastropods, the b ...

. On the base there are about 10 smaller cords irregularly spaced. The axis is perforate by a narrow twisted umbilicus. The axial sculpture consists of very fine close uniform sharp incremental lines. The simple

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 ...

is rounded-quadrate. The thin outer

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 ...

is sharp, undulated by the sculpture. The body of the shell is lightly glazed. The inner

is slightly tortuous, hardly thickened, with a slight angle at the anterior end.Dall (1919) Descriptions of new species of Mollusca from the North Pacific Ocean; Proceedings of the U.S. National Museum, vol. 56 (1920)
/ref>

Distribution

This species occurs in the Eastern Russian Arctic waters and off Southern

Hokkaido is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The la ...

at depths between 50 m and 550 m.

References

* Hasegawa K. (2009) ''Upper bathyal gastropods of the Pacific coast of northern Honshu, Japan, chiefly collected by R/V Wakataka-maru. In: T. Fujita (ed.), Deep-sea fauna and pollutants off Pacific coast of northern Japan''. National Museum of Nature and Science Monographs 39: 225–383. {{DEFAULTSORT:Margarites Rossicus rossicus Gastropods described in 1919