Littorina saxatilis (Olivi, 1792)
Circumboreal to Massachusets, to Puget Sound, to Iberian Peninsula; Azores to Mediterranean; also found in San Francisco Bay. Grazer on diatoms and algae from the supralittoral and the high intertidal, in crevices and other shelters such as underside of stones and dead barnacles in areas exposed to sea spray, down to shallow subtidal grounds in lagunar systems and salt marshes. Also detritus feeder. This is a rather young species that originated in the NE. Atlantic about 0.65Myr ago.

Under stone at Malamocco, Venice lagoon, NE. Italy. 8-8,5mm.
Top: saxatilis s.s.
Botttom: variant “rudis”.
 
This is a highly polymorphic species, which can vary in shape, size, thickness, sculpture colour and pattern; hence the huge number of variants and synonyms, such as var. “aurantia”, “conoidea”, “fasciata”, “laevis”, “sulcata”… or albocinctus, intermedia, marmorata, patula, rudis… – Above: the species in Dautzenberg & Fischer: Mollusques provenant des campagnes de l’Hirondelle et de la Princesse-Alice dans les mers du Nord, Monaco 1912, plate X.
Top: variant “lugubris”. Botttom: variant “tenebrosa”.
Op. cit. plate IX.
For more informations about the variability of saxatilis, see Galindo & Grahame: “Ecological Speciation and the Intertidal Snail Littorina saxatilis”, Advances in Ecology vol. 2014, article ID 239251.
A “tenebrosa” Montagu from Barents Sea. Intertidal algae, in a cove facing Teriberka, Kolsky District, Murmansk Oblast, NW. Russia. Original picture provided by D. Ivanov for iNaturalist – (CC BY-NC).
A rounded “tenebrosa” Montagu. On rocks, Kilitbahir, northern coast of Dardanelles Channel, across from Çanakkale, Western Marmara Province, NW. Turkey. 12,5mm.
A specimen from the Gulf of Saint-Lawrence.
Original picture provided by C. Nozères for WoRMS.
– (CC BY-NC-SA) –
Variations on a single rock south of Duncan’s Cove, Halifax, eastern coast of Nova Scotia.
Original picture provided by J. A. Ellrich for WoRMS.
– (CC BY-NC-SA) –
Different variants from the sheltered shallow muddy cove of Run Traou, located at the eastern root of the Sillon de Talbert, north of Lézardrieux, NW. Brittany, NW. France. 9-16mm.
Intertidal, Mer Mélen, east of the Sillon.
On rocks at low tide, Storang Creek, southern coast of Groix Island, S. Brittany, NW. France. According to johncrothers from the iNaturalist community, this is a variant of saxatilis. This group, often met in rough water, is characterized by a strong spiral sculpture. The variation affects also the animal’s colours.
Other variant from 5m deep, Savudrija, Umag, Istria Comitat, NW. Croatia. 7mm. Original pictures provided by N. Lete (HR).
(CC BY-NC-SA)
Forti San Luċjan, Marsaxlokk, SE. coast of Malta. 14mm. Original pictures provided by A. Nappo (IT).
(CC BY-NC-SA)

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