A new approach allows morphological recognition of cryptic diversity of the krill genus Hansarsia (formerly Nematoscelis)

Abstract Cryptic and pseudocryptic species are found on all major branches of the tree of life and probably represent a significant portion of undiscovered biodiversity, yet their identification is currently possible solely on the basis of molecular analyses. Here, we tested an alternative approach and hypothesized that all genetic clades might be identified on a morphological basis, and we analysed the morphology of nine previously detected genetic clades of Hansarsia. We made 169 sets of measurements (12 quantitative characters for each), ran multinomial logistic regression models, and showed a high ability of these models to generalize (i.e. to be able to classify correctly new specimens not included in our data matrix). The five to seven most ‘powerful’ characters provided a significant detection rate; these characters were shown to represent distinct evolutionary traits. Our findings cast some doubt on the presence of the ‘merely’ cryptic species; instead, we suggest that any genetic divergence found via traditional genetic markers is also mirrored in morphological divergence and can be detected using a combination of quantitative characters and appropriate mathematical tools. We provide a script key to genetic clades of the Atlantic Hansarsia based solely on morphological measurements and encourage other researchers to use quantitative morphological characters for detection of cryptic clades in other taxa.