When did the first species of the genera Tonicella Carpenter, 1873 and Boreochiton G.O. Sars, 1878 (Mollusca, Polyplacophora) appear in the Atlantic Ocean?

Abstract

It is assumed that the species of the genera Boreochiton G.O. Sars, 1878 and Tonicella Carpenter, 1873 originated in the North Pacific Ocean. The first representatives of these genera apparently penetrated into the northern part of the Atlantic Ocean not earlier than the Pliocene. Fossil representatives from the Late Cenozoic deposits of Europe, belonging to the genus Tonicella, have a sculpture of a tegmentum closer to the species of the genus Lepidochitona Gray, 1821, which suggests their transfer to this genus.