Trilobites within nautiloid cephalopods

'Sheltered preservation' of the remains of trilobites within the shells of nautiloid cephalopods is not especially uncommon. In most cases, of course, both the trilobites and the nautiloids were dead, and the association, mer ely due to post-mortem happenstance. However, on the basis of state of pres ervation and occurrence, a number of live individuals of the trilobite gene ra Acidaspis, Flexicalymene, and Isotelus from the Ordovician of the United States and of Alcymene and Encrinuraspis from the Silurian of Wales and th e Czech Republic seem to have entered conchs of dead cephalopods, presumabl y for refuge.