At the bottom of the Serripes zone, the fauna changes with the arrival of species previously unknown in the area. These include common whelk, Neptunea despecta, Serripes, Macoma calcarea and the wrinkled rock-borer (Hiatella arctica), but these species are now among the most common species of shellfish in Iceland. Around 80 species of molluscs, mainly snail and bivalve species, have been found at the Serripes zone. In Breiðuvík in Tjörnes, about 125 meters wide sedimentary layers are formed in part by a marine sediment containing the remains of marine animals, especially forams, crustaceans and molluscs.