Periwinkles are a large family of gastropod molluscs found on the shore. The edible periwinkle is perhaps the best known species of this family, as it has been collected and eaten for centuries. After boiling, the soft body is ‘winkled out’ from the shell with a pin or a special ‘winkle-picker’ (3). This species is the largest periwinkle found in Britain. It has a dark grey or black conical shell that develops a smooth surface with age. The flattened tentacles bear obvious black bands, a feature which allows young specimens to be identified easily. Males can be distinguished during the breeding season by the presence of a penis on the right side of the body (4).
The flat periwinkle grazes on detritus and microorganisms. It also feeds on green seaweeds such as sea lettuce (Ulva lactua) and species of Enteromorpha(2).
Breeding may take place throughout the year, but tends to vary depending on temperature (4). The sexes are separate (individuals are either male or female), and fertilisation occurs internally after copulation (2). Egg laying is timed to coincide with the spring tide; the eggs are laid in the sea in gelatinous capsules that usually contain around three eggs (although up to 9 eggs per capsule has been known) (4). The egg capsules float in the sea and free-swimming ‘veliger’ larvae hatch after a few days. After 6 weeks spent in the ocean, the larvae settle on the shore. The young periwinkles attain sexual maturity at two or three years of age and may live for up to five years (2).
Jackson, A. (2002) Littorina littorea. Common 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: http://www.marlin.ac.uk/species/Littorinalittorea.htm
Fish, J.D. and Fish, S. (1989) A student’s guide to the seashore. Unwin Hyman Ltd., London.
Buczaki, S. (2002) Fauna Britannica. Hamlyn, London.
Jackson, A. (2002) Littorina littorea. Common periwinkle. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme. [On-line]. Plymouth: Marine Biological Association of the United Kingdom. (November, 2003) http://www.marlin.ac.uk/species/Littorinalittorea.htm
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