Gibbula magus (Linnaeus, 1767)
Shetland & Irish Sea, English Channel to Mauritania, Canarias, Mediterranean. Grazer and deposit feeder from the upper subtidal down to 200m deep, on various rocky or sedimentary bottoms: maerl, detritic sands, silty grounds etc.

Original taxon: Trochus magus. Synonyms: bicarinatus, forskadauri, major, protumida, tuberculatus, vulcanica…
On soft bottom, Bay of La Spezia, Liguria, NW. Italy. 25mm.
Variants alba, dilatata, elata, obsoleta, producta, turbinosa…
25m deep, on gravel bottom, Cabo Noli, Spotorno, Savona, Liguria. 27mm.
A delicate specimen from near Atlantic, found in 2-3 feet of water, on rock, El Argoub, Ad Dakhla, Western Sahara. 18mm.
Variations in sculpture and colours.
Dredged in sand bottom at 2-5m deep, Deltebre, mouth of Ebre, Tarragona, Catalunya, NE. Spain. 16-25mm.
Variation set, collected on sand, mud and gravel, in the channel between Berder island and the town, Larmor-Baden, Morbihan, S. Brittany, NW. France. 21-24mm.
Same spot, in stone and gravel. 22-27mm.
You can notice the presence of two albida in this lot, especially the one at top right. A distinctive feature is given by the umbilicus: wide open in magus, almost always closed by a callus in albida.
The animal in Forbes & Hanley: A history of British Mollusca and their shells vol. I, London 1853, plate DD.
 
« This fine shell is found all round our coasts, though not everywhere in equal abundance. It is most vividly coloured in southern localities. A white variety was noticed by Mr. Jeffreys in the Hebrides and Zetland. It lives in from 3 to 25 fathoms water, and is most abundant in from 10 to 15 fathoms. » – F. & H.: op. cit. vol. II, London 1853, p.525.
By night in a few meters deep, Anse de la Touesse, east of Rothéneuf, Saint-Malo area. Original picture provided by P. Corbrion for iNaturalist – (CC BY-NC-SA).
Young specimens can be confused with G. albida Gmelin.
Pointe du Chevet, Saint-Jacut de la mer, N. Brittany. 14-18mm.
Same spot, near Les Ébihens islet.

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