''Perotrochus atlanticus'' is a species of

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 in the family

Pleurotomariidae Pleurotomariidae, common name the "slit snails", is a family of large marine gastropods in the superfamily Pleurotomarioidea of the subclass Vetigastropoda. This family is a very ancient lineage; there were numerous species in the geological pas ...

Description

The shell has a typical trochoid shape with a spire angle of approximately 80 degrees and nearly smooth sided until the later whorls which are clearly gradated with a clearly defined suture. The base is flat with an angular periphery and a well defined

columellar Lucius Junius Moderatus Columella (; Arabic: , 4 – ) was a prominent writer on agriculture in the Roman Empire. His ' in twelve volumes has been completely preserved and forms an important source on Roman agriculture, together with the ...

callus at the center covering roughly 40 percent of the base area. The aperture is oval, the slit is positioned roughly halfway between the periphery and the suture and is long, about 20 percent of the circumference. The shell is heavily textured with about 20 to 22 coarse spiral cords crossed by numerous heavy axial growth lines to produce rows of prominent beads over the entire surface above the selenizone (the area where the shell growth filled in the slit) and about 7 to 8 rows of prominent beads below. The base has 29 to 35 spiral ribs which are finely beaded. The

protoconch A protoconch (meaning first or earliest or original shell) is an embryonic or larval shell which occurs in some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod. In older texts it is also called ...

and primary whorls are white and the rest of the shell is creamy overlaid with numerous irregular brown to purple-red axial flammules, the base is creamy with lighter brown to purple-red flammules, and the interior of the aperture is

nacre Nacre ( , ), also known as mother of pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is f ...

ous. The shell is regularly found without a

periostracum The periostracum ( ) is a thin, organic coating (or "skin") that is the outermost layer of the shell of many shelled animals, including molluscs and brachiopods. Among molluscs, it is primarily seen in snails and clams, i.e. in gastropods and ...

. The operculum is small, roughly circular, dark brown, multispiral, and chitinous. Size range: 46 to 88 mm diameter.Anseeuw, P. & Goto, Y., ''The Living Pleurotomariidae'' (1996), Elle Scientific Publications, Osaka Japan, pp. 202, at pp. 60–61.Original description: E.C. Rios & H.R. Matthews, in ''Journal of Estacao de Biologica Marinha, Universidad Federale do Ceara'' (1968) Vol. 8, "''Novs Especie de Pleurotomariidae do Brazil''.

Distribution

This species is found at depths of 130 to 280 meters on sand or mud bottoms from southern Brazil south to the border of Uruguay.

References

External links

* Pleurotomariidae Gastropods described in 1968 {{Pleurotomariidae-stub