Scientists find giant, fugitive clam famous as ‘the unicorn of mollusks’

For hundreds of years, biologists knew of a hulk shipworm usually from bombard fragments and a handful of passed specimens. Those specimens, notwithstanding being recorded in museum jars, had left to mush. Still, a shipworm’s sparse stays done an outsize sense on biologists. Its three-foot-long tubular shells — a shipworm isn’t technically a worm yet a bivalve — were so distinguished that Swedish taxonomist Carl Linnaeus enclosed a animal in his book that introduced a systematic fixing complement “Systema Naturae.”


And nonetheless no one could get their hands on a vital instance of a hulk shipworm, or Kuphus polythalamia. Unlike with other shipworms, named given they ate their approach into a sides of wooden boats, no one knew where a hulk shipworm lived.

“It’s arrange of a unicorn of mollusks,” Margo Haygood, a sea microbiologist during a University of Utah, told The Washington Post.

The medium of a world’s longest clam is a poser no longer. As Haygood and her colleagues reported Monday in a Proceedings of a National Academy of Sciences, a hunt for a hulk shipworm has come to an end.

Television news in a Philippines dealt a mortal blow to a shipworm’s near-mythical status. A TV hire aired a short documentary shred about bizarre shellfish vital in a lagoon. The uncover filmed a mollusks flourishing in a muck, as yet someone had planted rows of elephant tusks. As fitness would have it, a co-worker of Haygood’s in a Philippines held breeze of a segment. Researchers investigated the lagoon, where they plucked a live shipworm from a mud, slipped it along with some seawater into a PVC siren and shipped the animal to a laboratory.

“I’ve been investigate shipworms given 1989 and in all that time we had never seen a vital citation of Kuphus polythalamia,” Daniel Distel, a co-author of a new investigate and a executive of Northeastern University’s Ocean Genome Legacy Center, wrote in an email. “It was flattering fantastic to lift that tube out of a enclosure for a initial time.”

Distel carefully chipped divided during a hulk shipworm’s large shell. Smaller shipworms are obese pink, beige or white, as are many clams. Not a hulk shipworm. Its physique is black.

“To see this hulk gunmetal black citation was amazing,” Distel said. “On a one palm we was flattering vehement to see what it looked like inside. On a other palm it was a tiny intimidating to disintegrate this impossibly singular specimen.”

A mature hulk shipworm reaches up to 3 feet long, that means that when draped opposite a breadth of a twin bed, a clam would usually hardly fit. “It’s utterly heavy. It’s like picking adult a tree bend or something even heavier,” Haygood said. “The vital animal is usually magnificent.”


(University of Utah)

What’s more, a hulk shipworm hardly has a digestive system. “It’s not feeding in any normal way,” Haygood said.

The clam has a mouth and a tiny stomach, yet a gills are supersize. Living within those gills are bacteria. That’s not surprising for shipworms: The clams, as a rule, have symbiotic relations with microbes. Usually, though, a microbes assistance shipworms digest wood.

In a box of a hulk shipworm, a scientists found grains of sulfur packaged into a bacteria. The sea biologists think that, during some indicate in a shipworm’s evolution, a animal traded a wood-digesting germ for germ that feed off sulfur compounds.

The investigate “provides a fascinating instance of symbiont displacement, a phenomena we are usually usually commencement to observe some-more frequently in nature, interjection to advances in sequencing that have supposing us with a collection to uncover a evolutionary story of microbes,” said Nicole Dubilier, executive of a Max Planck Institute for Marine Microbiology, who was not concerned in a study. “What we are now saying is unexpected: symbioses are not as fast as we formerly assumed.”

The symbiotic arrangement between bacillus and hulk shipworm was identical to one found in deep-sea hydrothermal vents. Thousands of feet next a surface, over a reaches of sunlight, tube worms also get their nutrients from germ that devour sulfides. Despite their identical names, though, tube worms and shipworms aren’t tighten relatives. Tube worms are annelids — they’re tangible worms, like earthworms, not clams.

But a symbiotic germ in both deep-sea worms and a lagoon-living clams are associated to any other. “So this is a box of meeting evolution,” Distel said. That is, both the worms and clams independently arrived during a same conclusion: Housing bacteria inside their bodies was a excellent approach to stay nourished.

Haygood pronounced a participation of the sulfide-consuming germ suggested that a lagoon, perhaps filled with rotting timber or other organic matter, produced hydrogen sulfide.

The find lends support to a hypothesis proposed by Distel in 2000 about a origins of animals that live in deep-sea vents. In Distel’s theory, mussels that lived in wood and harbored a sulfide-eating germ competence have sunk to a vents. Far below, they flourished on sulfide expelled from a vents.

“Wood supposing an ecological bridge, assisting them to invade a vents,” he said. The find of a new shipworm indicated that shallow lagoons could have served as the location for a switch in germ types: First a timber served directly as food for clams. But once the clams began to take in a sulfur-loving bacteria, a timber supposing a source of a hydrogen sulfide for a microbes.

“This is an intensely singular instance where we were indeed means to find sincerely approach justification about how this sold symbiosis evolved,” in that a clams traded one form of germ for a other, Distel said.

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