A deep water patellogastropod from oligocene water-logged wood of Washington State, USA (Acmaeoidea: Pectinodonta).

Late Oligocene concretions from the shores of the Strait of Juan de Fuca, Washington State, USA contain limpets that represent the earliest record of the taxon Pectinodonta. Assignment of these specimens to this taxon is based on scanning electron microscopy of shell microstructure and their intimate association with fossil wood. Shell microstructures in the Pectinodonta consist of an outer calcitic homogeneous/simple prismatic layer followed by a calcitic foliated layer, an aragonitic comarginal crossed lamellar layer, myostracum, and an aragonitic cone complex crossed lamellar layer. A size class analysis of pectinodontids from different pieces of fossil and Recent wood suggests that few cohorts are found on any single piece of wood, and we speculate about possible factors that may produce this pattern. Lastly, we describe Pectinodonta palaeoxylodia Lindberg & Hedegaard new species and associated taxa from this water-logged wood community.