Lutraria lutraria is a species of large marine bivalve mollusc in the family Mactridae. Its common names include the otter shell and the common otter shell. It occurs in coastal regions of the north east Atlantic Ocean where it lives buried in the sand. Taxonomy Lutraria lutraria is the type species of the genus Lutraria, the name Mya lutraria being the basionym used by Carl Linnaeus when he described the species in 1758. It was later determined that there were sufficient differences between it and other Mya species for the otter shell to be placed in its own genus. The similarity between Mya and Lutraria is due to convergence due to exploitation of the same habitat rather than a close phylogenetic relationship.<ref name=CM>[http://sabella.mba.ac.uk/1293/01/Cleansing_mechanisms_and_the_function_of_the_fourth_pallial_aperture_in_Spisula_subtruncata_%28A_Costa%29_and_Lutraria_lutraria_%28L%29..pdf Cleansing mechanisms and the function of the fourth pallial aperture in Spirula subtruncata and Lutraria lutraria]</ref> DescriptionL. lutraria has a pair of large, elongated oval valves up to long. They are smooth, glossy and fairly thin. They are a creamy colour and the periostracum is olive brown. This layer gets worn away over time and is often completely missing in shells found on the beach. There are concentric sculptured lines showing periods of growth and a few faint radial lines near the hinge. The left valve has two cardinal teeth with a third small one behind. The right valve has two small cardinal teeth and a small lateral one. The flesh of the animal is white. The foot is thick and protrudes through the pedal gape at the posterior end. The mantle edges are fringed with white and are fused together. The massive siphons can be extended to two or three times the length of the shell and are joined together for their entire length. They are streaked with brown and purple and are housed in a transparent, gelatinous sheath composed of protein and chitin. The siphons are outgrowths of the mantle while the sheath is a continuation of the periostracum. There are two rings of tiny tentacles round the orifice of the inhalant siphon and a single ring and a membrane round the exhalant one.The British species of Lutraria (Lamellibranchia), with a description of L. angustior The mantle has a fourth pallial opening near the base of the siphon. <div align=center> Right and left valve of the same specimen: </div align=center> DistributionL. lutraria is found off the coasts of north west Europe from Norway south to