Body shape variations help to diminish taxonomy uncertainty in juvenile swimming crab Callinectes Stimpson, 1860

Abstract The American continent harbors thirteen species of the genus Callinectes, eight of which are distributed in Atlantic South America. This genus has three identification keys for adult individuals only, proposed by Williams and Melo. The first one uses sexual characters to distinguish the species, which prevents the identification of juveniles due to the presence of a sealed abdomen. The other two are similar, both use the form and arrangement of the carapace teeth and have never been systematically tested on juveniles. Therefore, no formal identification keys have been proved to be useful for identify juvenile Callinectes based on any characters. Consequently, there is a lack of baseline studies in taxonomic variation regarding the differences between individuals of this genus. In this study, we investigated the suitability of identification keys, developed for adult individuals of the genus Callinectes, for juvenile individuals. Therefore, we evaluated the degree of dissimilarity of the body shape using the 2D landmark geometric morphometric technique. We compared the results of intra- and interspecific body shape with the key descriptions proposed by Williams and Melo for adults. This study included 537 individuals (juveniles and adults) and is the first effort to propose diagnosis for juvenile Callinectes, demonstrating that the carapace shape is a variable structure with potential to identify juveniles of these species. The results of mean body shape showed the possibility of extending the identification keys developed for adults to earlier ontogenetic classes (juveniles) when analyzed in conjunction with more distinguishable morphological characters tested in this study.