''Brachytoma rioensis'' 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

Pseudomelatomidae Pseudomelatomidae is a family of predatory sea snails, marine gastropods included in the superfamily Conoidea (previously Conacea) and part of the Neogastropoda ( Bouchet & Rocroi, 2005). In 1995 Kantor elevated the subfamily Pseudomelatomina ...

Description

The length of the shell varies between 15 mm and 25 mm. (Original description) The fusiform shell is pale brown with whitish ribs. It contains 9

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. The two whorls in 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 ...

are smooth, convex, and form a maminillar apex. The rest are concave above the convex, oblique ribs (ten on the penultimate whorl) with transverse tubercles on the middle caused by spiral lirae passing over them. The tubercles are more pronounced upon some of the upper volutions than upon the last two or three. In the upper concavity the threads are finer than those below. 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 ...

is attenuated in front and finely lirate throughout. The aperture is white within. The outer lip shows a strong external

varix A varix (pl. varices) is an abnormally dilated vessel with a tortuous course. Varices usually occur in the venous system, but may also occur in arterial or lymphatic vessels. Examples of varices include: * Varicose veins, large tortuous veins usua ...

a little way from the thin brown finely denticulate edge. The posterior sinus is moderately deep and rounded :The columella is smooth, with a thin callus united above to the end of the outer lip. The anterior canal is slightly recurved. Two of the spiral lirae around the middle of the whorls are more conspicuous than the rest, and much more distinctly nodulous. The fine growth lines are sinuose, and most evident at the upper part of the whorls.Smith, E. A. 1915. Mollusca. Part I.--Gastropoda Prosobranchia, Scaphopoda, and Pelecypoda. British Antarctic ("Terra Nova") Expedition, 1910. Natural History Report. Zoology 2 61–112, pls. 1–2. British Museum (Natural History): London
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Distribution

This marine species occurs off Eastern & Southern Brazil at depths between 73 m and 125 m.

References

* Daccarett, E. Y. & Bossio, V. S. 2011. ''Colombian Seashells from the Caribbean Sea''. L'Informatore Piceno. 384pp.

External links

* * {{DEFAULTSORT:Brachytoma Rioensis rioensis Gastropods described in 1915