Abstract
Mediterranean underwater marine caves harbour abundant populations of several species of mysids that are increasingly used as biological models in ecological and evolutionary studies. One exception is the species H armelinella mariannae , described in 1989 and then hardly ever again reported in the literature. We here provide the first data on the distribution of this poorly known taxon that, contrary to expectations for a rare brooding cave dweller, we now report from M adeira I sland in the nearby A tlantic, to the easternmost parts of the M editerranean. Brief behavioural observations are added, particularly its atypical solitary habits and its feeding behaviour as a high trophic level carnivore. Molecular characterization of the different specimens captured provided three sorts of information. Mitochondrial COI and 16 S haplotypes suggest different colonization waves in the M editerranean, with one group in the E astern B asin, two in the M arseille region in the NW part of this sea, and another group with a very wide extension from M adeira to L iguria and M alta. Mitochondrial data also support that one of the groups in M arseille might have diverged as a cryptic species of H armelinella . 18 S r RNA gene displays a single common sequence to all specimens from the four groups, and seems to confirm the original proposed placement of this taxon within the subfamily H eteromysinae, not L eptomysinae.