Tide pool at East Point Sanctuary near Biddeford Pool, Maine. Tentative identifications of organisms in this tide pool: Common Periwinkle (Littorina littorea), a snail that is an invasive exotic species introduced in North America in the nineteenth century; limpets (mollusc spp. in family Lottiidae); Blue Mussel (Mytilus edulis); barnacles (crustacean spp. in subclass Cirripedia); Knotted Wrack, a seaweed (Ascophyllum nodosum).