Читать книгу Extreme Nature - Mark Carwardine - Страница 19

NAME	isopod Cymothoa exigua
SIZE	up to 4 cm long
ABILITY	eating and then mimicking the tongue of the spotted rose snapper fish

© Matthew Gilligan

This is probably the world’s most specialised and gruesome isopod – one of a group of crustaceans including woodlice, marine gribbles and slaters. Most isopods lead perfectly normal lives as herbivores, scavengers or carnivores, but some are parasites. Cymothoa exigua has a tendancy to select the mouth of the spotted rose snapper fish for its hangout.

Latching on to the fish’s tongue with its hooked legs (pereopods), it feeds on mucus, blood and tissue, gradually eating away the tongue. Gripping onto the tongue stub, the isopod then effectively becomes the fish’s tongue, growing as its host grows and feeding on particles of meat that float free as the fish eats. The biggest individual isopod recorded was 39mm (1.5in), but presumably it can grow to be as big as the fish needs its tongue to be.

Perhaps the practice is not as gruesome as it looks, as the rose snapper can continue to feed, but no one knows whether a time comes when Cymothoa decides to let go and get a taste of blood in someone else’s mouth. Strangely, the relationship between the fish and its parasite has been observed only in the Gulf of California, or Sea of Cortez, though the fish is found in the eastern Pacific, from Mexico to Peru. It is the only known example of a parasite replacing not just a host’s organ but also its function (to hold prey) – a hard act to swallow.