Shell turbinate, semitransparant, with 5 to 6 whorls. Few (2-3) adapical spiral cords on basal whorl that are much stronger than the axial sculpture and have much broader interstituals than other spiral cords. The 3 most basal cords grow higher than the ones more adapical of the base. Outer lip not dentate within. Protoconch with microsculpture of fine spiral elements.

Diagnostic characters
Shell with large last whorl, rather small spire and markedly turreted profile. Surface with prominent spiral keels, the most adapical on each whorl the largest, the space between them marked with numerous little costae. Aperture large, pointed adapically, outer lip with thick varix. White. One metapodial tentacle.
Other characters
The shell is semitransparent, with 5-6 whorls, the most adapical part of each forming a shelf nearly at right angles to the shell axis. The 2-3 most adapical spiral ridges on each whorl are the best developed and lie far apart; those on the base of the last whorl form (1) an adapical group of 5-7, low and close together, and (2) a basal group of three higher ones lying further apart. All spaces between spiral ridges show a series of numerous, narrow costellae. The outer lip arises level with spiral 3 and is much thickened by a varix; this is absent in juvenile shells where the lip is thin and slightly scalloped by the ends of the spiral keels; some trace of this may persist in adult shells. Juveniles also show an umbilicus, closed later. Up to 4mm high, 3mm broad; last whorl occupies about three quarters of the shell height, the aperture about half.
The animal has the general appearance of all rissoids, but the snout is longer and narrower than usual and the neck has small lobes, one on each side. The flesh is cream, the buccal mass showing through the snout wall as a red area.
A. carinata lives under stones lying on sandy areas of beach at L.W.S.T, and to depths of about 25 m. It is found sparsely in south west England and rarely further north; probably absent from the eastern part of the Channel, the North Sea and the northern parts of Scotland. It is a southern species, extending to the Mediterranean. The reproduction is unknown: Thiriot-Quievreux & Babio (1975) believe development to be direct.

It is an easily recognizable species, with a rather well defined spiral sculpture made by carinae more or less broad (particularly the subsutural one), with interspaces finely lamellated. These spiral carinae are of different solidity (see photo), so that Monterosato (1884) described the variant ecarinata which has the spiral sculpture less broad, smaller sizes and, often, some varices. Moreover this form seems to be the most common one, while the variant varicosa /Marshall, 1893), having big varices, is more uncommon. The colour pattern is uniform white, rarely yellowish in colour. The average measures are abt. 4 mm in heigth.

Distribution: it is found in a large part of the Mediterranean, but never common. Also in the Atlantic up to UK and Nordsea.
Habitat: it lives on muddy-detrital bottoms of the infralittoral plain.