As Chrysodomus nuceus Dall, 1919:
Shell small for the genus, solid, yellowish, rather acute, with six whorls exclusive of the (lost) nucleus, suture distinct, narrow, deep; spiral whorls flattish behind the periphery at which there is an obscure angle; in front of this are a few obscure spirals, indicated by color rather than elevation in the type-specimen; incremental lines inconspicuous rather rude; aperture white, outer lip sharp, slightly expanded; body and pillar with a thick white enamel; canal short, recurved, with a strong fasciole. Height of shell, 62; of last whorl, 50; diameter, 35 mm. (Dall.)
TYPE in United States National Museum, No. 151429. Type locality, Cook's Inlet, Alaska.
RANGE. Arctic Ocean to Cook's Inlet, Alaska.

Shell large (usually between 100 and 175 mm, occasionally up to 200 mm, dwarfs from 55 mm are known), rather thick, solid, occasionally heavy. Colour variable, ranging from white or yellowish over pale brown to dark reddish brown, usually uniform, occasionally with a darker or paler spiral band. Whorls convex, subsutural slope slightly concave. Upper spire whorls smooth or with weak, obscure spiral cords. Interspaces narrow. Penultimate whorl with numerous fine spiral cords of different strength, of which 2 or 3 occasionally stronger. Axial sculpture consisting of fine incremental lines. Occasionally with a labral varix.

Shell. At a superficial glance this shell looks like a ribless Buccinutn undatum: there are, however, numerous other differences. It is solid and opaque, not glossy, and has usually lost the periostracum. The spire is slightly coeloconoid, with a blunt tip, the apical angle 50-60°. There are 7-8 tumid whorls meeting at shallow sutures placed well below the periphery of the upper whorl. The subsutural area of each whorl, more particularly those of the spire, shows a tendency to become flat, imparting a slight angulation to the profile. The last whorl is large. The ornament consists of spiral and growth lines. The former are fine, numerous, and reduced or absent on the subsutural area. They are usually of different size, repeated in a pattern, so as to give a slightly striped appearance to the surface, but they may be all alike. Growth lines are still more numerous; they are prosocline near the suture but become flexuous away from it. A thick spiral keel, the siphonal fasciole, runs from the base of the canal to the umbilical region, sometimes separated from the columellar lip by a groove; there is no umbilicus.
The protoconch is rather bulbous, consists of about 1.5 whorls, and is smooth, with incipient spiral lines; it measures about 1 mm across.
Aperture. A large oval or pyriform opening, angulated adapically, and tapering to a broad siphonal canal at the base. It lies in a slightly prosocline plane and is surrounded by a peristome. The outer lip arises a little below the periphery of the last whorl perpendicular to the surface there, and so t. 140-150° to the shell axis. It follows a nearly semicircular course to the canal; its edge may be thin and a little reflected in juveniles but often thickens in old specimens. It is rather straight near its origin and shows a shallow sinus below this straighter part. The canal is short, wide, and open. The columella is long, not quite straight, its lip everted. Over the last whorl, especially in old animals, the inner lip may thicken and join the outer.
Colour. Yellowish, sometimes with a reddish tinge. The throat usually of a deeper tint, bur the peristome remains pale.
Size. Commonly about 100 x 5 mm, but occasionally half to twice as big again. Last whorl = 70-80% of total shell height; aperture = 55-65% of total height.
Animal. The head consists of a transverse fold bearing the tentacles and, on its underside, the mouth (= opening of a proboscis sac). The tentacles are rather long, each carrying an eye about half way along its length, the basal pan twice as thick as the distal. The mantle edge is plain, with a siphon on the left which docs not project far as the snail creeps. Males have a large penis.
The foot is large, with the anterior end double-edged, nearly straight, a little extended at each lateral point. The posterior end is rounded, and carries an oval operculum, pointed at one end, where the nucleus lies, females show the opening of a ventral pedal gland in the anterior half of the sole.
Colour. Yellowish, sometimes slightly reddish, sometimes with many small black speckles, which are most conspicuous on the siphon. The sole of the foot is yellow, the operculum dark.
Geographical distribution. A north Atlantic species occurring from the Bay of Biscay to the Arctic. It is found all round the British Isles, though rarer in the south and off western Irish coasts. It occurs throughout the North Sea and extends into the Baltic Sea as far as the Lübecker bucht, though there often stunted. Common in many sites.
Habitat. Never intertidal, but on all kinds of bottom, mainly soft, from about 15 to 1200 m. It lives in water whose temperature lies between 3° and 17°C and whose salinitv is 29-35%c (Golikov, 1963).

Neptunea antiqua exhibits remarkable variation and is known to consist of a large number of populations, most of them well distinguishable. A number of populations are found to be contiguous to each other and geographically isolated from the next. Further study may produce their recognition as subspecies, at present we still regard them as variants (form);

* Neptunea antiqua "Norway form"
Specimens from along the northern boundary of the range have a characteristically glossy shell with fine spiral sculpture. The shape is broad, the spire high. The whorls arc convex with a rather broad, slightly concave subsutural slope and a distinct suture. The aperture is wide, usually with a flaring outer lip. The colour is white or pale brown; the columella is occasionally silver in colour. Remarkable difference in size is recorded, individuals from the same population grow to an adult size of between 90 mm and 177 mm. Specimens are collected off Bergen, the southwestern coast of Norway and off the Shetlands. Further study may involve its recognition as a subspecies. The Doggersbank form is similar in shape and sculpture but differs in having a slightly coarser sculpture and a yellowish colour. The Celtic form may have a similar smooth surface but differs in having a heavier shell, a smaller aperture (shells from the northern Celtic Sea) and a simple outer lip.

* Neptunea antiqua "Doggerbank form" Specimens from the northern part of the North Sea have a characteristically large shell with convex whorls, distinct suture and large aperture, smooth surface and uniformly pale colour. Some shells have a yellow or orange aperture. This phenotype was named form ventricosa by Jeffreys.

* Neptunea antiqua "Scotland form"
Specimens from along the coast of north and north-east Scotland show a mixture of characteristics imposed by the surounding populations. The shells are quite large (usually larger than the Northsea form but smaller than the Doggersbank form), heavy (like the Celtic form) with rather convex whorls, white in colour (like the Celtic form) but occasionally with an orange aperture (like the North Sea form) and a variable sculpture of fine spiral cords of different strength. Some specimens are smooth. The boundary of these populations is not clear yet, and we may assume that they form a continuum in between the surrounding populations. It may be hard to distinguish these Scottish shells, nevertheless we have decided to keep them separated as a distinct form.
The heavy white shell with yellow aperture described by Da Costa as Buccinum magnum is probably this form.

* Neptunea antiqua "North Sea form"
Specimens from the central and southern North Sea are somewhat similar to the Doggersbank form, but differ in having a smaller shell with shallower suture, rather colourful pattern (shading from pale yellowish over reddish to brown, often with darker axial streaks). When freshly caught these shells may have bright pastel colours, which will fade over time. Some specimens are ornamented with a broad spiral band, slightly darker or paler.
Specimens closer to the coast of The Netherlands have a more orange-reddish colour, a slightly stronger but still fine and regular
spiral sculpture and a smaller size. Although these shells are easy to recognize, they fit well within the variability of the North Sea form.
Several populations off the western coast of Denmark arc characterized by having a smaller size and an often bright yellow or orange aperture. Although these shells arc easy to recognize, they also fit well within the variability of the North Sea form.

* Neptunea antiqua "Channel form"
This dwarf form, mainly from south eastern England and occasionally caught by fishermen off north France, has a characteristically small, rather heavy, brownish shell, occasionally with slightly anguiated whorls and a dense sculpture of numerous fine spiral cords of equal strength. The aperture is usually broad with a slightly flaring outer lip. The colour and axial pattern is similar to the North Sea form but usually darker. The angular shoulder reminds us of the Red Crag specimens (fossil Neptunea antiqua and sinistral Neptunea angulata (Wood, 1848) from the late Pliocene to early Pleistocene of south eastern England).
Shells arc frequently collected on the beaches of Walton on the Naze (Essex) to Sandwich. These populations are bathymetrically separated from typical Neptunea antiqua and further study may involve their recognition as a subspecies.

* Neptunea antiqua "Celtic form"
Specimens from off the Cheshire Coast (south west England) and Liverpool Bay have a characteristically thick and heavy, snow white shell, usually with a broad shape, a short spire and a large aperture. The spiral sculpture consists of fine, occasionally obscure, spiral threads. This phenotype was named form alba by Jeffreys. Shells from off northern Ireland and north west Scotland usually have a smoother surface and a slenderer shell, and arc often marked by growth-defects. The shells from Liverpool Bay arc often recorded as a subspecies. If further study confirms a subspecies status, the name alba Jeffreys, 1867 is preoccupied fourfold by Fusus albus.

* Neptunea antiqua "ocean form"
Specimens from of the Atlantic coast of Ireland (forexample Nymphe Bank and off Galby Head, County Cork) have a characteristically large shell with strong spiral sculpture. This phenotype was named form striata, and the slenderer shells were named form gracilis by Jeffreys. The colour ranges from white to brown. Specimens with an orange aperture are named form browni by Dautzenberg and Fisher. These shells with their prominent spiral sculpture have a very similar appearance to Neptunea despecta, even more similar than some smoother forms of Neptunea despecta itself. A combination of polymorphism (variability within the population) and acline (gradually stronger sculptured specimens towards the west), together with a sufficient number of intermediates, links the Atlantic form with the more eastern forms. Here again we have a good example of a wide phenotypical overlap.

* Neptunea antiqua "southern form" Shells are recorded from deep water in the Gulf of Biscay. Further study will confirm whether these belong to one of the known forms or to a distinct population.

* Neptunea antiqua "Baltic form" This brackish water form has a characteristically small, thin shell. They may be the end of a clinc, from the saline North Sea through Kattegat and Skagerrak into the brackish water of the Baltic, or geographically and ecologically different. Further study may involve its recognition as a subspecies.

* Neptunea antiqua "Porcupine form"
This form lives several hundred meters deep on Porcupine Bank. This is the westernmost locality known to us. The shell is small and brown. Further study may involve its recognition as a subspecies.

* Many form names have been used for aberrant specimens. Much sought after are lefthanded shell. Very rare at present, such specimens with sinistral chirality were more frequently found in old English collections. This curiosity was named "monstr. contrarium" by Jeffreys. Shells with an compressed base in combination with a deformed, strongly twisted siphonal canal, are known from off The Netherlands and from the Celtic Sea. This monstrosity was named "monstr. uncinata" by Henrard. Tabulated shells are rare. This monstrosity was named "babylonicus" by Brown.

Uncertain to the north and west. It is common in S Scandinavia and around the British Isles. 15-1000 m (Seaward, 1982; Pearce & Thorson, 1967).

Range and habitat: Neptunea antiqua is restricted to the European Atlantic coast. It is known from the Gulf of Biscay in the south, along the British Islands and the European mainland, to Bergen (southern Norway) and the Faroe Islands in the North. The southern boundary of the range is limited by the warm Atlantic. The northern boundary of the range is limited by the cold water of the north Atlantic, in particular by the strong seasonal fluctuations in temperature north of the Shetland and Faroe Islands. The northern boundary of the range is eventually extended towards the Faroe Islands and the south Norwegian coast under the influence of warm water from the North Atlantic Current (Gulf Stream). Some shells offered to collectors and labelled as trawled off Vigo (northwest Spain) are proved as belonging to the form from the southern Celtic Sea. Neptunea antiqua was, together with Neptunea despecta, erroneously recorded from Japanese waters. Already in 1895 however, Pilsbry carefully worded his doubts about these: "Both antiquus and despectus have been credited to northern Japan. We have not seen Japanese specimens" (1895: 28).