Pliocene hermit crabs (Decapoda, Anomura, Paguroidea) preserved in situ in host gastropod shells from the San Diego Formation near San Diego (southern California, USA)

One three- dimensionally preserved, near- complete specimen and five in-situ preserved partial specimens of hermit crabs are recorded from the San Diego Formation (middle Pliocene, Piacenzian) of San Diego and Chula Vista, California, USA, respectively. On the basis of features of their near- complete shields, two of these are assigned to members of the family Calcinidae FRAAUE, VAN BAKEL & JAGT, 2017, namely Dardanus sp. and Sandiegocalcinus calvanoi n. gen., n. sp. Three other individuals with fewer carapace remains preserved, or none at all, are left in open nomenclature as indeterminate paguroids (Paguroidea LATREILLE, 1802 s.l.). For the first time, preserved calcareous plates of the posterior membraneous part of a paguroid carapace and a gonopod on the coxa of P3 in Dardanus sp. are reported from the fossil record. The San Diego Formation material enlarges our limited knowledge of extinct hermit crab communities of Pliocene age in southern California.