During a zooplankton survey carried out off the coasts of the bay of Toulon, France, several monstrilloid copepods were collected. The systematic analysis of this group allowed the identification of males and females of Monstrilla grandis GIESBRECHT, a male of Cymbasoma tenue (ISAAC), and a male of a new species of Monstrilla. Monstrilla grandis is a cosmopolitan species, which has been recorded previously in the Mediterranean but has not been adequately described, this is particularly true for the male, which is fully described herein. The specimen of C. tenue, a species redescribed recently, has some interesting morphological variations and its description is amended. The new species of Monstrilla, M. pygmaea n.sp., is very closely related to M. helgolandica CLAUS and to M. serricornis SARS. The new species can be distinguished mainly by its extremely small size, by details of the ornamentation of the terminal antennular segment, the structure of the genital lappets, and by its body proportions. Inglés