Perotrochus atlanticus is a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of sea snail

Sea snail

Sea snail is a common name for those snails that normally live in saltwater, marine gastropod molluscs....

, a marine gastropod mollusk in the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Pleurotomariidae

Pleurotomariidae

Pleurotomariidae, common name the '"slit snails", is a family of large marine gastropods in the clade Vetigastropoda. This family is very ancient; there were numerous species in the geological past. It is currently represented by a group of species that live only in deep water...

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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 gradate with a clearly defined suture. The base is flat with an angular periphery and a well defined columellar callus at the center covering roughly 40 percent of the base area. The aperture

Aperture (mollusc)

The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....

 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

Protoconch

A protoconch is an embryonic or larval shell of some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod...

 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 nacreous. The shell is regularly found without a periostracum

Periostracum

The periostracum is a thin organic coating or "skin" which is the outermost layer of the shell of many shelled animals, including mollusks and brachiopods. Among mollusks it is primarily seen in snails and clams, i.e. in bivalves and gastropods, but it is also found in cephalopods such as the...

. The operculum

Operculum (gastropod)

The operculum, meaning little lid, is a corneous or calcareous anatomical structure which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails...

 is small, roughly circular, dark brown, multispiral, and chitinous. Size range: 46 to 88 mm diameter.

Distribution

This species is found at depths of 130 to 280 meters on sand or mud bottoms from southern Brazil

Brazil

Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

 south to the boarder of Uruguay

Uruguay

Uruguay ,officially the Oriental Republic of Uruguay,sometimes the Eastern Republic of Uruguay; ) is a country in the southeastern part of South America. It is home to some 3.5 million people, of whom 1.8 million live in the capital Montevideo and its metropolitan area...

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External links

• http://www.gastropods.com/3/Shell_2293.shtml Gastropods.com images