''Retidrillia megalacme'' 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 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 ...

Borsoniidae Borsoniidae is a monophyletic family of small to medium-sized sea snails, marine gastropod mollusks in the superfamily Conoidea.Bouchet, P. (2011). Borsoniidae. Accessed through: World Register of Marine Species at http://www.marinespecies.o ...

.Bouchet, P. (2015). Retidrillia megalacme. In: MolluscaBase (2015). Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=832444 on 2016-03-23

Description

The length of the shell attains 5 mm, its width 2.5 mm. (Original description) The small shell has a conical-fusiform shape. 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 ...

is well raised and fairly solid. Its colour (dead) is whitish-brown, with a white

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 ...

. It contains 6. turreted whorls, regularly increasing. The white protoconch is large. The first

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 ...

and a half are smooth, then closely set longitudinal riblets are seen, and the whorl becomes carinate. The remaining whorls are acutely carinate, with an area below the suture, either smooth or with arcuate striae. Below the carina appear numerous longitudinal riblets, decussated by spiral carinations, giving the shell a somewhat prickly or nodulous appearance. The

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 small, with a well-marked sinuation above. The columella is vertical, a little twisted at the base.Sykes E. R. 1906 ''On the Mollusca procured during the “Porcupine” Expeditions 1869–1870. Supplemental notes, part 3.'' Proceedings of the Malacological Society of London 7: 173–190
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Distribution

This species occurs in the Atlantic Ocean off

Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of ...

References

* Sykes E. R. 1906 On the Mollusca procured during the "Porcupine" Expeditions 1869–1870. Supplemental notes, part 3. Proceedings of the Malacological Society of London 7: 173–190. * McLean J. H. (2000). ''Four new genera for northeastern Pacific gastropods.'' The Nautilus. 114: 99–102.

External links

Bouchet P., Kantor Yu.I., Sysoev A. & Puillandre N. (2011) A new operational classification of the Conoidea. Journal of Molluscan Studies 77: 273–308.
{{DEFAULTSORT:Retidrillia Megalacme megalacme Gastropods described in 1906