Allometric ontogenetic changes in two Late Jurassic gastrodorid hermit crabs (Crustacea, Decapoda, Anomura) from central Europe

Extinct anomurans are known mostly by their carapaces. Regions in the fossil carapace are well delimited by grooves and, by comparison with extant hermit crabs, they can be referred to the underlying internal organs. In this paper we examine the allometric effects in ontogeny of two Jurassic hermit crabs of an extinct genus Gastrodorus: G. neuhausensis von Meyer, 1864 and G. bzowiensis sp. nov. described herein. Both species occur in Oxfordian and Kimmeridgian strata in southern Poland, but the former species only in southern Germany. Samples of carapaces of both species consisted of carapaces of a wide size range, illustrative of the various ontogenetic stages. A reduced major axis was applied for assessment of allometry. The most pronounced positive allometric effect in both species concerned the posteriormost region of the cephalothoracic shield, which became disproportionally more elongated than the overall carapace length (positive allometry) as overall size increased. Statistically significant differences between the two species concern the cardiac region, which gained in length with size in G. neuhausensis (positive allometry) and became proportionally narrower in the new species (negative allometry). Thus it may be assumed that overall growth rate of the heart region was less in the latter species. Additionally, new terminology of carapace regions previously introduced to pagurids and based on morphology of recent representatives is applied to the gastrodorids.http://zoobank.org/urn:lsid:zoobank.org:pub:E64D2515-BD0D-4A78-83A7-D35C5F9FA3E5