Type locality: "O. Septentrionali" (Linn. 1758); "O. Septentrionali" (Linn. 1767); prob. Holocene post- glacial deposits of Uddevalla, Sweden (Nelson & Pain, 1986: 299). Description: Shell medium to large (usually between 80 and 140 mm, occasionally up to 200 mm, adult specimens as small as 51 mm are known from the White Sea), variable, from thin to heavy and solid. Shape variable, whorls from convex (deep water) to angulated (usually shallow water). Subsutural slope straight or slightly convex, penultimate or body whorl occasionally concave. First spire whorl with 2 (occasionally 1) fine spiral cords and some fine axial ribs, occasionally reticulate. Upper spire whorls with 3 primary spiral cords. Interspaces usually with some fine secondary spiral cords. Axial sculpture consisting of fine incremental lines, occasionally axial folds. Range and habitat: Neptunea despecta is a boreal to Arctic amfi-Atlantic species. In the west Atlantic from Newfoundland and Nova Scotia (W Atlantic form) in the south to the entrance of Davis Strait in the north. From Tukingassoq Kigataq (a little north of Disko, western Greenland) (form fornicata), east Greenland (typical form), Iceland (fornicata and typical form) towards the east. From the Faeroe Islands in the south, along the coast of northern Norway and the Kola Peninsula (Russia) (typical form).Found far inside the White Sea (a dwarf form). Known from the continental shelf in the whole southern Barentz Sea (deep water form). The eastern boundary of the range is situated off western Waigats Island and at western Nova Zembla and is limited by colder water from the Polar Ocean and the influence of fresh water from the Kara Sea and fluctuations in salinity. Recorded as far north as above 82° N, between Svalbard and Franz Jozef Land by Warén (1989: 128-129). Bathymetric range from sublittoral (White Sea), 8 m (northwestern Norway), 20 m (form fornicata at western Greenland) to 800 m in the Barentz Sea (Golikov, 1963: 155). Earlier authors occasionally recorded Neptunea despecta, eventually together with Neptunea antiqua, from Japanese and Far East Russian waters. For example Zaks (1933: 21) recorded a specimen of Neptunea tuberculata and of Neptunea nodositella n. sp.

Comparison: Neptunea despecta exhibits remarkable variation in shape and sculpture and it is hard to produce a description which will fit all specimens. We recognize four main groups, here regarded as forms:
* Neptunea despecta "typical form". Typical specimens of Neptunea despecta (off Norway and southern Barentz Sea) have a somewhat angulate shape and many spiral cords (primary and secondary) of different strength.
* Neptunea despecta "West Atlantic form". Specimens from eastern Canada are rare. The shape is slender, usually with a peculiar high spire. Anyone who believes the form needs a name may use "form clenchi". Similar specimens are found off western Greenland (the area of "form fornicata").
* Neptunea despecta "form fornicata". Specimens from off southern and western Iceland, Greenland and Newfoundland usually have an angulate shape with shouldered whorls and strong axial sculpture. A single specimen is known from off northern Norway (pers. comm. and coll. Dmitry Alexeyev). This phenotype was named fornicata by Fabricius. It is often recorded as a subspecies by previous authors. We consider fornicata as an ecophenotype for the following two reasons. The first is that typical Neptunea despecta are collected in southern Iceland sympatrically with form fornicata and intermediates. This suggests that, if further study proves fornicata as distinct, a specific status (instead of a subspecific) is required. Secondly, the fact that the presence or absence of axial folds is not a valuable indication for differentiating Neptunea, and except in this matter we found no structural differences. "Differs from the nominotypical subspecies in the presence of characteristic narrow and convex regularly spaced axial folds on the upper part of the whorls.... The spiral keels are comparatively narrower than in the nominotypical subspecies and often slightly wavy due to the presence of the folds. The subspecies fornicata does not differ from the nominotypical one in any other conchological and anatomical features." (Golikov, 1963: 157, translated from Russian). Another fact is that specimens of this form are found throughout the range from Newfoundland in the west to southern Barentz Sea in the east. However, mainly in two places (west Iceland and west Greenland) separated from each other (southeast Greenland) by populations with typical shells. We consider this form diverged under the influence of warm water currents. Off west Iceland the Irminger Current (which branches from the North Atlantic Current) flows, bringing warm and saline water. Off west Greenland we find the West Greenland Current bringing saline and rather warm water. It is known that water from west Iceland, and for example larvae from cod and other fish, are transported from west Iceland by the Irminger Current, around southern Greenland by the East Greenland Current and towards west Greenland by the West Greenland Current (Hovgard & Buch, 1990). Both ecosystems (west Iceland and west Greenland) are linked and have more in common than warm water alone. The populations of fornicata are quite recent, as the west coasts of Iceland and Greenland were uninhabitable, beyond reach for the species, during the cold Pleistocene. Until now no fossil records have been found, "All mentioned species, which exist today in the Atlantic, are also found as fossil (except N. despecta fornicata)." (Strauch, 1972: 21, translated from German). If fossil material is collected, and study proves a different phenotypical branch, for example by a pre-Pleistocene migration and stock along the west coast of Greenland, then fornicata may be proved to be a distinct species.
* Neptunea despecta "deep water form”. The populations from deep water off Svaldbard, Nova Zembla and central Barentz Sea, have a thin, whitish shell with convex whorls and a rather smooth sculpture also on the upper teleoconch whorls. These populations are bathymetrically separated from typical Neptunea despecta and further study may involve their recognition as a subspecies or distinct species.

Neptunea antiqua differs in having quite convex and rather smooth upper teleoconch whorls, bearing only some low spiral cords (in the northern and eastern populations). Sculptured forms (Ocean form) of Neptunea antiqua are hard to distinguish from Neptunea despecta. Smooth forms of Neptunea despecta are quite hard to distinguish from Neptunea antiqua. Both species are syntopic off the Faeroe Islands (pers. comm. and coll. Christiane Delongueville and Roland Scaillet). Neptunea lyratodespecta lyratodespecta Strauch, 1972, a fossil from the N. E. Atlantic Pliocene, and ancestor of Neptunea despecta, differs in having stronger spiral cords. Neptunea denselirata is similar in shape and some specimens are easy to confuse with Neptunea despecta, but are distinguishable by the smaller adult size, the high spire and the dense spiral sculpture (if the secondary spiral cords are present), as well as the finer secondary spiral cords separated by narrow but planar interspaces.