The shell shape and sculpture are very variable in this species (de Aranzamendi et al., 2009; Gonzalez-Wevar et al., 2011a). The species exhibits a conical morphology, dorsally raised with a very thick and non-translucent shell. The anterior part of the animal is laterally compressed. The shell is large (maximum length 140 mm), with a high profile. The apex is situated at the anterior 40-50% of the shell's length. All the slopes of the shell are convex. The aperture of the shell is oval. The surface of the shell is sculptured with raised angular primary radial ribs, weaker secondary ones and concentric growth lines across the interspaces. The margin of the shell is highly crenulated. The external coloration of the shell is very variable in the species across its distribution (pale reddish brown, white with dark lines, grey, green and brown). The primary and secondary ribs are brown ash-coloured to dark brown, with clearer interspaces. The internal part of the shell has soft metallic brown coloration with dark lines corresponding to external colour patterns, bordered by a white/brown halo. External anatomy: The ventral area of the foot is light grey and the epipodial fringe is recognizable. The mantle fold is thick and dun-brown coloured. The mantle tentacles are in alternate series of three white shorter and a white longer one and are absent of pigmentation. The cephalic tentacles are dorsally pigmented with a black line.

The species is highly abundant, with a continuous distribution along Pacific Patagonia from Chiloe Island to Cape Horn, including fjords and channels, the Strait of Magellan and Tierra del Fuego, Cape Horn, Hornos Islands and Diego Ramirez Islands. In the Atlantic, N. magellanica is also highly abundant up north to the Rio Negro Province. However, along the Atlantic coast the distribution and abundance of N. magellanica depends on the availability of suitable rocky habitats. Similarly, N. magellanica is highly abundant in the Falkland/Malvinas Islands. Nacella magellanica comprises a single genetic unit throughout Pacific and Atlantic Patagonia, with Falkland/Malvinas Islands populations detectably different Molecular and geometric morphometric comparisons showed that N. chiloensis and N. venosa are synonyms of N. magellanica (Gonzalez-Wevar et al., 2011a).

Magellanic province. Pacific Patagonia from Chiloe Island to Cape Horn. Atlantic Patagonia from Tierra del Fuego to the Rio Negro Province. Falkland/Malvinas Islands.
Habitat: High and medium intertidal rocky ecosystem between 0 and 25 m depths.