Rough Periwinkle (Littorina saxatilis complex)
The shells of this group of species have spiral ridges which give it a rough feel ( a common
name is the rough periwinkle). It tens towards the upper part of the shore and favours
crevices in the rocks. The shells are very variable in colour, as shown here. Some scientists
have split this group into a number of seprate species because of this variability