Littorina littorea - common periwinkle

	DISSEMINATION

Geographic Range	it is commonly found on the rocky coasts of Europe and of North America.
Physical Characteristics	the shell may be up to 50 millimeters long, it is conical with a pointed apex. The spiral ridges are clearly marked in young individuals, while they tend to become more obscured in the adults, giving the shell a smoother appearance. The shell colours are usually grey-black-brown-red but they are generally black or dark grey-brown, often lighter towards the apex and usually patterned with spiral lines. The columella of the central axis of the shell is white. The cephalic tentacles are rather flat and broad with a lot of transverse black barring.
Notes	this species tends to join in order to form clusters in the most suitable zones (such as puddles rather than dry zones). They are more active when they are under water, because moving on mucus they employ less energy. The sexes of this species are separate, the female may produce up to 100.000 eggs, which are laid after insemination.
Habitat	it is distributed on rocky coasts. If the environmental conditions are good it may also settle in sandy or muddy habitats such as estuaries and mud-flats. It is rather tolerant of brackish water. It lives on the substrate surface.
Food habits	it is herbivorous, it feeds mainly on green, brown and red alga.

Sources
References	MarLIN: The Marine Life Information Network for Britain & Ireland Invertebrate Zoology - Laboratory Exercises - Littorina littorea, by Richard Fox - Lander University, South Carolina
Web References	http://www.marlin.ac.uk/ http://www.lander.edu/rsfox/310littorinaLab.html
Source of the photo	http://privat.egersund.com/erling/Blotdyr/page4.htm