Two female snapper-choking isopods Cymothoa excisa (body length 11 and 14 mm) were in the buccal cavity of two invasive lionfish Pterois volitans (total length 294 and 301 mm) collected in Alacranes Reef, southern Gulf of Mexico. This is the first record of C. excisa parasitizing invasive lionfish P. volitans in coral reefs of the Western Atlantic, where these isopods appear to have infected the host through adult prey-predator transfer.