Described in French (click French flag)

Shell. Immediately recognizable by its sinistral coiling. It is solid, opaque and glossy, a tall, narrow cone of c. 15 whorls of which 11 are post-larval. The spire has an apical half with sides converging at an angle c. 30°, and a basal half with sides converging at c. 9° so that the whole is cyrloconoid. The whorls are nearly flat-sided (neglecting the ornament) and meet at shallow sutures just below ihe periphery of the upper whorl. The upper edge of the suture is defined by a spiral ridge. The ornament consists of spiral ridges and grooves which transverse costae intersect to give a tuberculatcd surface. There are 5-6 spiral ridges on the last whorl, the adapical 3 crossed by costae and tuberculate, the lower 2-3, below the periphery, smooth or slightly nodose in the neighbourhood of the aperture. On the spire the lower 3-4 whorls have each 3 tuberculated spiral ridges, the next 6-7 have 2, and the topmost 1-2 whorls only 1. The ridges are broader than the intervening furrows and steeper on the adapical than the abapical faces. The costae are slightly opisthocline and about as broad as the intervening spaces. They tend to be crowded together near the aperture. There are 20-23 on the last whorl and about 2 fewer on successive whorls up the spire. Where costae and spiral ridges cross tubercles form; they are usually rather square elevations but often a little elongated in the direction of the costa; this is pronounced near the aperture. There is a fine reticulation of spiral and growth lines in the hollows of the ornament, the latter sometimes marked, and this is always true of those on the base of the shell.
The protoconch is long, c. 500 µm high and 320 µm across. It has 3.5-4.5 whorls. The first (embryonic) bears irregularly scattered tubercles; the others have numerous, fine, transverse lines which cross 1 (in the upper whorls) or 2 (in the lower) equally fine peripheral spiral lines. The transition to the adult pattern is abrupt. Aperture. Squarish, with a peristome lying approximately in the axial plane. The outer lip arises from the adapical untuberculated spiral keel and runs, continuing the outline of the spire, to a point between the 3rd and 4th spiral ridges; it then turns through nearly 90° towards the columella below which it is turned out to form a short and narrow siphonal canal pointing to the right and with its tip directed a little back from the aperture. The outer lip is thin and scalloped by the ends of the spiral ornament. The columella is short and the peristomial edge everts over it so as to leave a slight umbilical canal but no umbilicus. Over the last whorl the lip forms a rather thick glaze. The throat is glossy. Colour. Yellow-brown, the edge of the inner lip chocolate; the tubercles and apex may be paler. Size. Up to 7x2 mm. Last whorl = 30-35% of total shell height; aperture = 20-25% of shell height.
Animal. The head carries a very short snout, dorsoventrally flattened, the opening of the proboscis pouch a longitudinal slit on the underside. The tentacles are long and slender, slightly thickened at the tip; an eye lies on a low bulge at the base of each. The mantle skirt is plain, drawn out into a short siphon on the right, which lines the siphonal canal. The pallial organs are reversed, the ctenidium on the right, the anus on the left. The pallial genital duct is closed in the female but open in the male, which has no penis. The foot has a broad, rather square anterior end, slightly pointed laterally. The propodium lies above the mesopodium so that the anterior pedal gland opens on the dorsal surface of the foot. The hinder end is pointed and the sole has a median longitudinal groove in its posterior half to which a larger posterior pedal gland opens. The operculum is multispiral. Colour. White; tentacles clear white.

Geographical distribution. From the N. coast of Spain to W. Norway, the Kattegat and Kiel Bay in the Baltic Sea. Absent from most of the southern North Sea and eastern Channel basin. Habitat. T. adversa may be found on the lowest stretches of rocky shores, usually associated with the sponges Halichondria and Hymeniacidon, often partly or wholly embedded in their tissues. It may also be found under stones, or algae, and sublittorally to 100 m.