Mesolithic populations from coastal areas are known as hunter-gatherer-fishers. This way of life is visible in the landscape owing to the presence of large accumulations of shells named shell middens. These anthropogenic refuse heaps are composed of high proportions of marine resources, yet studies dedicated to marine components are relatively recent. Efforts have been made to record marine molluscs, but other minorities are still invisible as a result of the small sizes of archaeological remains. Crustaceans are one of these minorities and this article will focus on one of them: crabs. Why are these decapods persistently ignored by most of archaeologists? Is this due to the scant presence of their remains in Mesolithic shell middens? An overview of published data on crabs is presented here for the Mesolithic period on the European Atlantic facade. The proportions of shell middens comprising these crustaceans is evaluated, as well as quantities and identified species. We endeavour to identify the potential impact of excavation methods and sampling on our knowledge of this marine resource. We present the methods developed to extract data from small archaeological crab remains and show how, from a fragment of a crab finger extremity, we can identify the species and estimate the original size of crabs. This methodological challenge has a major impact on our knowledge of past maritime populations.