Who wouldn't love a black worm that smells like a toilet, is longer than Danny Devito is tall, looks like a player in a tentacle horror venue, and doesn't eat?

Perhaps calling Kuphus polythalamia a worm is a bit pejorative. The animal, encountered alive for the first time just now (though scientists have known of its existence for centuries), is a shipworm.

Shipworms are not real worms. They are bivalves – in other words, they're elongated clams.

As for the diet, normal shipworms eat wood. They are pests. Before ships were made of metal, shipworms ate them too, as well as piers, boring into water-saturated wood with their specially evolved shells. Shipworms, Teredinidae, can be impressively large too, reaching a couple of feet in length.

Pretty much nothing was known about their cousin Kuphus. Its tube-shaped shells had been spotted since the 1700s, but the animal had never been encountered alive.

Then, analyzing video footage, scientists noticed them planted like carrots in a sulfurous swamp in the Philippines. They set up an expedition and found live specimens, which have now been formally studied for the first time.

First off, they're huge: Kuphus is typically three to five feet in length. Oddly for a mollusk, its body (inside the shell) is black. Like any clam, it lives inside its calcium shell, which is mostly buried – the creature grows downward, into the mud. And it doesn't eat, at least in any way we think of as eating.

The animal lives in a muddy swamp rich in organic material, which emits hydrogen sulfide, H2S, a gas based on sulfur that smells like rotten eggs. To Kuphus, that's dinner. Extraordinarily for a large animal, it is chemoautotrophic – which means it lives off inorganic mineral sources.

Most chemoautotrophs are bacteria, best known from deep-sea vents. Kuphus is among the mollusks that can live off inorganic material, thanks to its symbiotic relationship with sulfur-eating bacteria.

Open gallery view Life clusters around a deep-sea vent: Crabs and barnacles, for instance. Credit: A. D. Rogers et al. in PLoS Biology, Wikimedia Commons

Normal shipworms cannot actually digest wood. They evolved special valves that bore into water-soaked wood but digestion depends on gut flora. Kuphus' bacterial symbionts live in its gills.

Plants use solar energy to convert CO2 and water into sugars that the rest of the food chain eats: that is photosynthesis. The worm's guest bacteria perform chemosynthesis, ingesting hydrogen sulfide for energy and produce organic carbon, which in turn feeds the worm.

One striking corollary, say the stunned scientists in the Proceedings of the National Academy of Sciences, is that many of Kuphus's internal digestive organs atrophied.

Dr. Daniel Distel of the Ocean Genome Legacy Center at Northeastern University suspects the animal's evolution from a wood-eating organism to one that eats mud gas was driven by the acquisition of a different type of beneficial bacteria. In other words, it seems that Kuphus' original cellulolytic symbionts were supplanted by sulfur-oxidizing bacterial invaders.

Apparently, "wood served as an evolutionary stepping stone for a dramatic transition from heterotrophy to chemoautotrophy," write the scientists in PNAS.

"We suspected the giant shipworm was radically different from other wood-eating shipworms," says senior author Prof. Margo Haygood of the University of Utah. "Finding the animal confirmed that."