Rissoa membranacea (J. Adams, 1797)
Norway to Ireland, Baltic Sea to Black Sea.
Grazer and detritus feeder in the upper infralittoral.
Original taxon: Turbo membranaceus.
Synonyms: grossa, labiosa, oblonga, plicatula
Shallow water, Grado, Friuli-Venezia Giulia, NE. Italy. 6mm.
« Colour yellowish brown, thin, pellucid, with oblique yellow-brown stripes, imperforated; readily distinguished by its membranaceous appearance. » – J. Adams: “Descriptions of some minute British Shells”, Transactions of the Linnean Society of London vol. V, London 1800, p.2.

Specimens from near Atlantic.
Subtidal, on Zostera nolti, in muddy bottom, Ria Formosa, Faro, Algarve, S. Portugal. 6-6,4mm.
Lanvéoc, Finistère, NW. Brittany, NW. France. 5mm.
Cap d’Agde, Hérault, S. France. 5-7,5mm.
The shell can be slender or stout, smooth to radially ribbed, with or without thin spiral striae. The pattern varies also, from absent to, as pictured above, densely marked of radial flamules that resemble a little those of Pusillina lineolata (Michaud, 1830). – Shallow water, southern shore of Salses-Leucate lagoon, Occitania, S. France. 6,1-6,5mm. A. Bertrand legit (FR).
Same spot. 7mm.
The brown and slender variant “cornea” Lovén, from sheltered brackish areas. Gore Cove, Moonfleet, West Fleet Lagoon, Weymouth, Dorset, S. United Kingdom. 8,3mm. Some specimens from this spot measure up to 9mm.
Subfossil collected in brackish ponds, Le Grau-du-Roi, Gard, S. France, 5,5mm.
Cale de Jouvente, Pleurtuit, western shore of the Bassin de la Rance, NE. Brittany, NW. France. Original pictures provided by P. Corbrion for iNaturalist – (CC BY-NC-SA).
Slender specimen from 5m deep, Split area, dalmatia, S. Croatia. Original picture provided by P. Ugarković (HR).
(CC BY-NC-SA)

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