Littorina obtusata, common name the flat periwinkle, is a species of sea snail, a marine gastropod mollusk in the family Littorinidae, the winkles or periwinkles. Distribution This marine species occurs wherever brown seaweeds grow. It is widely distributed : the Baltic Sea, in European waters from Norway down to Southern Spain, in the Mediterranean Sea, in the Northeast Atlantic Ocean along the Gulf of Maine. Description The maximum recorded shell length is 13.5 mm. Habitat This species can be found in the littoral and sublittoral zone on rocky shores and piers, usually on brown algae of the genus Fucus. Minimum recorded depth is 0 m. Maximum recorded depth is 110 m. The habitat may define its color. On sheltered shores it has a lighter and uniform color (yellow, brown, orange or olive green). On exposed shores its color is darker and chequered. References Notes Bibliography Backeljau, T. (1986). Lijst van de recente mariene mollusken van België [List of the recent marine molluscs of Belgium]. Koninklijk Belgisch Instituut voor Natuurwetenschappen: Brussels, Belgium. 106 pp Reid, D.G. (1989a) The comparative morphology, phylogeny and evolution of the gastropod family Littorinidae. Philosophical Transactions of the Royal Society of London, Series B 324: 1–110 Reid D.G. (1996). Systematics and evolution of Littorina. The Ray Society 463p BODC (2009). Species list from the British Oceanographic Data Centre External links Littorinidae Gastropods described in 1758 Taxa named by Carl Linnaeus