Who would like to carry a parasite? I bet not many people would like to have one or more. They are nevertheless very common in humans and in other organisms, and can affect entire food webs including keystone species. They tend to be small compared to the host and the vast majority of them are soft-bodied. Despite their small size and soft appearance, they can affect the host substantially, for example, leading to a reduced growth rate and less offspring.
Much of the same holds true for crustaceans – they are affected by parasites and can act as parasites themselves. For example, parasitic crustaceans are found among the isopods and copepods. Given the widespread occurrence of parasitism in and by crustaceans today, a fossil record of such parasitism may be expected.
Swellings in fossil crabs and squat lobsters
So what does the fossil record look like? I have been fortunate to have worked on this under-studied field of research. During my PhD research, I found various swellings in fossil crabs and squat lobsters (decapods from the superfamily Galatheoidea) during and after field work in northern Spain in reef carbonates from the mid-Cretaceous (upper Albian). They appeared to occur regularly in the back part of the carapaces of these crustaceans.