from Scientific American

Has a New 10-Legged Species Evolved beneath Rome?

By Rob Dunn

Crabs are alien. Their eyes stand up on stalks, waving without apology. Their ten legs each grasp the world, but mostly they keep to their realms of tidelands and sea bottoms. The river crab, Potamon fluviatile, sneaks along streams throughout much of Italy, Greece and nearby Malta, Albania, Croatia and Macedonia. It is, as crabs go, both interesting and ordinary. It is one of the crabs Aristotle would have seen, Homer too. It is a crab millions of children have grown up running from and toward—screaming regardless of the direction. It is not a crab about which one hopes to make new discoveries; then someone did.

People have been keeping an eye on the river crab because like many species of crustaceans and nearly everything else in rivers and streams, its populations have been declining. We do terrible things to rivers and the species living in them. You have seen some of those things, and unfortunately,  we do them nearly everywhere. Drop something into a river and it seems to disappear, and so we have dropped, dumped, poured and otherwise contaminated nearly every river in the world. In the Mediterranean we have been doing these things for thousands of years, especially in cities. As a consequence, crabs have gone locally extinct from most of the urban areas where they once lived.

Personally, I like crabs. You could not invent them if you did not know they existed. They are just a little too odd. Insects make do with six legs but crabs seem to need two extra sets. And then there are their eyes, which might as well be legs the way they can look up and around corners. They gather what falls toward them. Those humans interested in rebirth seem to like the idea of being reborn as tigers or eagles but by my accounting, a great many bodies are reborn as crabs.

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