information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Common flat periwinkle (Littorina obtusata)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.
Only coastal and marine records shown



A small periwinkle (up to 1.5 cm in height), it has a flattened spire and large tear-drop shaped aperture. The last whorl makes up about 90% of the height of the shell and the outer lip joins the body a little below the apex. The shell appears smooth but upon closer inspection is found to be finely reticulate. It is highly variable in colour (from olive green to yellow to banded and chequered patterns) depending on its habitat, with lighter shells being found in more sheltered shores. It may be confused with Littorina fabalis (syn mariae) in which the aperture is larger than the body whorl and the spire is even flatter.

Recorded distribution in Britain and Ireland

Common to all shores where brown seaweeds occur on all British and Irish coasts.

Global distribution



The flat periwinkle is almost always associated with fucoid algae, in particular Ascophyllum nodosum, Fucus serratus and Fucus vesiculosus from mid to lower tidal levels on rocky shores and occasionally into the sub-littoral. It is tolerant of low salinities and a wide range of exposure.

Depth range


Identifying features

  • Up to 1.5 cm in height.
  • Body whorl slightly larger than aperture.
  • Flat topped with minimal spire.
  • Variable colour, can be olive green, yellow, brown or patterned.

Additional information

Littorina obtusata lays whitish oval or kidney shaped egg masses on Ascophyllum nodosum, Fucus serratus and Fucus vesiculosus, and sometimes on rock surfaces. It takes up to four weeks for crawling young to emerge.

Listed by

- none -

Further information sources

Search on:


  1. Fish, J.D. & Fish, S., 1996. A student's guide to the seashore. Cambridge: Cambridge University Press.

  2. Hayward, P., Nelson-Smith, T. & Shields, C. 1996. Collins pocket guide. Sea shore of Britain and northern Europe. London: HarperCollins.

  3. Hayward, P.J. & Ryland, J.S. (ed.) 1995b. Handbook of the marine fauna of North-West Europe. Oxford: Oxford University Press.

  4. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

  5. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line]

  6. National Biodiversity Network (NBN) Atlas website. Available from:  Accessed 01 April 2017

  7. Picton, B.E. & Costello, M.J., 1998. BioMar biotope viewer: a guide to marine habitats, fauna and flora of Britain and Ireland. [CD-ROM] Environmental Sciences Unit, Trinity College, Dublin.


This review can be cited as:

Pizzolla, P.F 2008. Littorina obtusata Common flat periwinkle. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 15-08-2018]. Available from:

Last Updated: 17/04/2008