Shell. Specimens from British waters differ from those collected in Scandinavia in some important respects. In this and the following section the appearance of British shells is described first and the different features of Danish ones later.
The shell is solid, opaque, not glossy, covered with distinct periostracum. It is tall and conical with a sharp apex (apical angle 33-40°, usually 37-38°) and a nearly straight-sided profile, a little cyrtoconoid with most of the curvature near the apex so that the apical angle of young shells (up to 5-6 whorls) is c. 55°. There are 10 whorls which meet at distinct sutures set just below the periphery of the upper whorl and made wavy by the ends of the costae; these also give the spire a slightly stepped profile. The ornament consists of spiral ridges and grooves, costae and growth lines. The spiral ridges are rather strap-shaped, broader than the intervening grooves except sometimes in the subsutural parts of each whorl (especially the last whorl) where they may equal them. The subsutural ridges arc also broader than those more basally placed. Near the base a deep spiral gutter runs from the edge of the siphonal canal to the columella; between it and the columella) lip of the canal is a rounded boss with 4-6 spiral ridges and grooves. Above the gutter the last whorl bears about 13 spiral ridges; the whorls of the spire have about 5 apiece. Costae cross each whorl on the spire; they are slightly prosocline adapically, orthocline basally and so present a shallow concavity facing down the spire. On the last whorl the basal half of each cost a becomes prosocline again so that the whole is flexuous, though those by the outer lip are nearly straight. The costae are undulate in section, about as broad as the spaces between and die out just above the spiral gutter. There is usually a labial varix and the last whorl bears an additional 20-22, the next two up to 25, the more apical ones a gradually decreasing number. Costae are often offset from whorl to whorl. Growth lines and fine spirals cover the whole surface. Costae and spiral ridges interact to give a series of raised blocks, more or less square in outline.
The protoconch has 2.3 whorls, smooth. 900-1100 µm across.
Scandinavian shells are in general similar but have a squatter shape (apical angle 50-60 degrees), less we marked ornament, particularly in the elevation of the costae.
Aperture. Oval, pointed adapically, its long axis lying at 15° to that of the spire; it is surrounded by a peristome prosoclinally inclined at c. 20°. The outer lip arises tangential to the last whorl below the spiral ridge 5 and runs basally so as to continue the outline of the spire, sometimes showing a smal anal sinus; it then curves, below the periphery, to the opening of the siphonal canal with which it merges without any sharp boundary. The canal is short, oblique, widely open, its distal edge forming a prominent notch on the abapertural side of the shell. The columella is short and straight, its lowe edge forming a well-marked oblique boundary to the siphonal canal. The lip here is out-folded I cover about half the basal base and occludes any umbilicus. Over the last whorl the inner lip spread extensively, with a semicircular edge. The outer lip is thin, wrinkled (especially basally) by the end of the spiral ornament. Internally it thickens rapidly to form a ridge set with 6-9 longitudinally elongated teeth. Between the ridge and its edge the lip is limed the grooves underlying the external ridges. The columellar and parietal regions are also toothed, though less regularly, 3 teeth on the columella and 3-4 over the last whorl. The reticulate pattern of the shell shows through the expanded inner lip. These features are absent from young shells and appear with maturity, the teeth on the outer lip before those on the columella and inner lip; in early stages there is a deep groove within the outer lip. The whole throat is glossy and the columellar surface and inner lip are beset with many microscopic points.
The most marked differences between British and Scandinavian shells affect the aperture. In the latter it is slightly broader; the origin of the outer lip is at a sleeper angle to the last whorl; the edge of the lip is thin and crenulated throughout; The siphonal canal is more open; the spread of the inner lip over the last whorl is less; the internal ridge and its teeth are absent and [here arc no teeth on the columella and inner lip.
Colour. Generally light brown because of the periostracum. When that is lost the shell is white but commonly there is a dark brown-slale-nearly black band on the subsutural part of each whorl. On the last whorl an obscure dark band lies at the periphery especially near the outer lip and there may be another at ihc base above the spiral gutter. The boss below that, and the siphonal canal often remain while or light-coloured. The innermost pan of the columella, especially in young shells, is often brown, like the deeper parts of the throat.
Size. Up to 30 x 14 mm. Last whorl 60 - 70% of total shell height; aperture = 40 - 50% of total shell height. Breadth of British specimens = 50"/o of height; of Danish specimens = 60% of height.
Animal. Ihe head is a flattened, shelf-like structure with no snout, the mouth (= opening lo a proboscis pouch) a longitudinal slit under it. The anterior margin is convex and there are 2 slender tentacles, each with an eye about one fifth of the total length from the base. The proximal part of the tentacle is about twice the thickness of the distal part. The mantle edge is simple with a siphon on the left. This projects a long way from the siphonal canal in active animals. Males have a penis on the right side of the head, arising some distance behind the right tentacle and, at rest, recurved in the mantle cavity. There is a long, narrow, bipectinate osphradium alongside the ctenidium.
The foot is rather long; its anterior end has a double edge, a nearly straight from with markedly recurved lateral points. A ventral pedal gland opens medianly in the anterior half in females, but there is no ABO in either sex. The posterior end of the fool has a median V-shaped notch and the lobe on each side of this bears a short tentacle. The operculum is oval and small, with jagged sides.
Colour. Brownish with black and while irregular speckles.
Geographical distribution. From ihe Canaries and Azores north to Norway (Trondheim) and throughout the Mediterranean and Black Seas. It occurs commonly on all British coasts, though rare in central pans of ihc Irish Sea and ihe east coast of Scotland. In Denmark it extends into many fjords and penetrates the Baltic as far as Kieler Bucht.
Habitat. The animals occur from near LWST to about 15 m depih. the bulk of the populaiion being sublittoral on soft bottoms. Intertidal animals are common on rocky shores with patches of soft material into which they burrow, leaving the tip of the siphon exposed. They prefer well-oxygenated areas to dense black muds but like places with animal detritus, and are common in sandy patches in runnels of water at low tide. They also occur under stones. They can withstand a reduction of salinity to about 16 promille.