The last instar larva is described and illustrated for the first time, and compared with the known congeneric larvae from the Caribbean. Its peculiarities are: size reduction of dorsal hooks, the presence of a dorsal hook on segment 2, and the absence of dorsal hooks on segments 6-9. M. meurgeyi has a triangular ligula with 10 premental setae and 6 palpal setae. Notes on the ecology of this lotic sp. are provided.