Is This The Planet's Most Peculiar Parasite?

Don’t read this if you are in any way squeamish or have nightmares after watching TV movies!

There are many parasites the world over. This example is known only by its scientific name - Cymothoa exigua but it is generally considered one of the weirdest out there! Parasites often mean the demise of their host after a close and prolonged association with it. In general they tend to be a great deal smaller than their host – think about us and the lovely tapeworm! This one goes one better. If you think about a tapeworm replacing your liver, for example, you are along the right lines!

Like most parasites, Cymothoa exigua is small and only usually grows to about three or four centimeters in length. It is also classified as a crustacean and lives off the coast of California. Its host is the Spotted Rose Snapper, a harmless fish that no doubt would not have asked for a close friend such as this if it could!

Cymothoa exigua enters the snapper though the gills and then proceeds to its mouth. It then attaches itself to the tongue of the snapper. On the pictures, you can see the front three pairs of legs. It uses this to extract blood from the snapper using these legs. It takes so much blood that the tongue eventually atrophies and withers away.

So far, so gruesome. Could it get much worse than that? Well, the answer is of course, yes! With only a few muscle stubs left for a tongue, the snapper is left without a fairly important organ. So, what Cymothoa exigua does is attach itself to the muscle stubs and replaces the fish’s tongue with itself.

The fish then uses the parasitic crustacean as a normal tongue. The fish gets the use of a ‘tongue’ and Cymothoa exigua gets a constant stream of blood from its host via the muscle stubs of the tongue. Apart from replacing its host’s tongue, Cymothoa exigua does not seem to do any extra harm to the fish at all.

This is the only reported case in the whole of the animal kingdom of a parasite functionally replacing an organ belonging to its host. As such Cymothoa exigua is unique and, despite its obviously gross appearance, celebrated as such!

A few years ago, one of these little beauties was found in a fish in the UK that had been purchased in a supermarket. It led to speculation that the parasite had somehow moved to the European waters but this speculation was unfounded: the fish had been caught off the western seaboard of the United States and so was from its own area.

Written by RJ Evans