The discovery of a hermit crab (superfamily Paguroidea) preserved in the likely immature shell of an ammonite, Craspedites nekrassovi is reported from the Upper Jurassic of Moscow, Russia. This is the oldest undoubtable symmetrical hermit crab to date which is known from non-reefal environments. This new occurrence combined with the documentation of numerous sublethal and lethal injuries on ammonite shells in the same beds (probably produced by such paguroids), all suggest that the hermit crabs not only lived in ammonite shells but also hunted these animals. The proportion of damaged shells (including healed ones) varies in different Upper Jurassic ammonite genera from 1.2% in Kachpurites up to 9.3% in Craspedites. Among damaged Kachpurites only 6.25% survived attacks whereas among Craspedites the percentage of survivors was 87.5%. These data imply that Craspedites likely lived near the sea bottom and often encountered hermit crabs, whereas Kachpurites likely lived in the water column.
For more than a century from all Jurassic localities of Central Russia only large lobster-like decapods of the genera Eryma and Glypheopsis have been reported. The finding which is described in this article is the first Jurassic hermit crab known from Russia. What is especially interesting is that it is found not in a large quarry, but in a small outcrop which is located in a forest ravine in Moscow, 10 km from the Kremlin. This finding made it possible to explain the strange injuries occurring on ammonite shells in this and other localities of the same age.
There is no doubt that this Jurassic hermit crab that lived more than 1000 km east of its previously known relatives belongs to a new, unknown species or even a genus. The author, being a specialist in ammonites rather than hermit crabs, did not describe the new species in this article. This remains an interesting challenge for the future.
Paguroidea, Diogenidae, Craspeditidae, Upper jurassic, Ammonite shell morphotypes, Ammonite sublethal injuries