Flat periwinkle (Littorina obtusata)
|Size||Shell height: 15 mm (2)|
Not threatened (2).
Periwinkles are a large family of gastropod molluscs found on the shore. The flat periwinkle is so-called because the spire of the shell is flattened (2). The tear-drop shaped aperture is large (3), and the colour is variable depending on the habitat. It is usually olive-green but may be brown, yellow, banded or have a criss-cross pattern (2). Lighter colours are associated with sheltered shores (3).
This species is common on all British shores where brown seaweeds are found (3). It has a wide distribution in north-west Europe (2) and is found from Northern Norway to the south of Spain and is absent from the Mediterranean (4) (3).
This periwinkle is closely associated with brown seaweeds, especially Ascophyllum nodosum, Fucus vesiculosus and Fucus serratus on which it feeds. It occurs on the mid-shore to lower tidal levels and may occasionally occur in the sublittoral (2).
Breeding may take place throughout the year, but tends to reach a peak in spring and early summer (2). The sexes are separate (individuals are either male or female), and fertilisation occurs internally after copulation (2). The white egg masses are typically kidney-shaped or oval (3), and contain up to 280 eggs (2). They are usually laid on the fronds of the brown seaweeds on which the species feeds but may also occur on the rock surface (2). The crawling young hatch four weeks after the eggs are laid. The young periwinkles become sexually mature at around 2 years of age, and they typically live for a total of three years (2).
This species is not threatened.
For more on this species see:
Pizzolla, P.F. (2002) Littorina obtusata. Flat periwinkle. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme. [On-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 27/11/2003]. Available on-line at:
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- Sublittoral: a marine zone between the littoral zone (the shallow zone where light reaches the bed, subject to submersion and exposure by tides) and depths of around 200m.
National Biodiversity Network Species Dictionary (September, 2003)
- Fish, J.D. and Fish, S. (1989) A student’s guide to the seashore. Unwin Hyman Ltd., London.
Pizzolla, P.F. (2002) Littorina obtusata. Flat periwinkle. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme. [On-line]. Plymouth: Marine Biological Association of the United Kingdom. (November, 2003)
- Gibson, R., Hextall, B. and Rogers, A. (2001) Photographic Guide to the Sea & Shore Life of Britain and North-west Europe. Oxford University Press, Oxford.