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Crustaceans as hosts of parasites

A fossil squat lobster carapace from Italy with a swelling caused by an isopod parasite in the left gill region.
A fossil squat lobster carapace from Italy with a swelling caused by an isopod parasite in the left gill region.

Over the last decade, parasites in the marine fossil record have been increasingly studied. The scientific community has shown that part of the lack of knowledge about marine parasites in deep time is simply due to a lack of research. As far as crustaceans as hosts go, three study systems have been confirmed: isopod-induced swellings preserved in the gill region of decapod crustaceans, feminized crabs probably caused by parasitic barnacles, and an enigmatic arthropod attached to an ostracod.

The first-mentioned study system is – by far – the one with the most research potential because such swellings were already known from the Jurassic to the present-day. The trace fossil name for such swellings is Kanthyloma crusta. Targeted research since 2014 has increased the number of fossil decapod species known to have been infected by these isopod parasites to 128 species, a remarkable 45% increase. Nearly half of them are known from the Late Jurassic epoch, when particularly true crabs (Brachyura) and squat lobsters (Galatheoidea) were infested. We also carried out research on the largest fossil decapod assemblage from the Late Jurassic, the Ernstbrunn assemblage from Austria consisting of nearly 7000 specimens. Interestingly, some taxa are more heavily infested than others, showing that host preference was already established in the Jurassic. Moreover, infested individuals of two commonly infested species are on average larger than non-parasitized individuals of those species. Perhaps continued infestation throughout ontogeny and/or the selection of larger individuals by the parasites can explain this result. Such analyses had not been done previously on this study system. The isopod-decapod study system holds great promise for future studies.

Klompmaker A.A., Robins C.M., Portell R.W., De Angeli A. 2022. Crustaceans as hosts of parasites throughout the Phanerozoic. In: De Baets K., Huntley J.W. (eds) The Evolution and Fossil Record of Parasitism. Topics in Geobiology 50: 121–172. Springer, Cham.