In Europe there are about nine species in this genus, one of which is the rough periwinkle, Littorina saxatilis (Olivi, 1792). Another closely related (supposed) species Littorina tenebrosa (Montagu 1802) was thought to be distinct because of its different ecological requirements, but current studies have shown that it is not at all clear whether the two are indeed separate species or whether L. tenebrosa is perhaps merely an ecotype (an ecological form) of L. saxatilis.[3]
Littorina has given its name to the Littorina Sea, the geologic precursor of the Baltic Sea.
Distribution
The periwinkles are found on the seashore in the littoral zone and sublittoral zone in all parts of the world. In the Baltic they live within the influence of freshwater, and frequently become distorted in consequence.
Description
The thick, pointed shell is turbinated and has few whorls. The aperture is rounded. The outer lip is acute. The columella is rather flattened and imperforate. The operculum is paucispiral. The lingual teeth are hooked and trilobed. The uncini (small teeth on the radula) are hooked and dentated.[4]
Species
The type species:Turbo littoreusLinnaeus, 1758 restricts the species in this genus to the northern hemisphere, moderate and cold zones. The tropical species belong in other genera of the same family [5]
^Gosling, E.M. (2002). The periwinkle as a model in biodiversity studies: a geneticist's view. in Marine Biodiversity in Ireland and Adjacent Waters. Ulster Museum. publication no. 8
^Bandel, K. & D. Kadolsky (1982). Western Atlantic Species of Nodolittorina (Gastropda: Prosobranchia): comparative morphology and its functional, ecological, phylogenetic and taxonomic implications. Veliger 25 (1): 1-42.
