Shipworm used to be something that all sailors fear although it doesn’t attack them. Well, these chubby clams just can’t get enough of wood. And back then, these poor sailors are always on alert because their ships could break down any minute.
Technologies advanced and ships have been built of stronger, more robust materials such as iron and steel. The fear of shipworm has faded. In 2006 scientists discovered a new type of shipworm in freshwater bodies in the Philippines. But this one won’t accept your wood, this one eats rocks.
Although discovered a decade ago, this shipworm has eluded detailed study until last year when U.S. researchers cracked open a few rocks and took their strange occupants back to the lab. Their findings, published this week in Proceedings of the Royal Society B said that this shipworm loves limestone or sandstone.
The locals, who actually eat the worms, suggested researchers to search the bottom of Abatan River on Bohol Island in the Philippines. While diving, the researchers noticed large chunks of sandstone dotted with holes. Upon closer look, researchers noticed the telltale twin siphons of the six-inch, sausagey shipworms protruded out of some of the holes.
“That was when we knew we’d struck shipworm gold,” said Reuben Shipway of Northeastern University, lead researcher and a marine biologist at Northeastern University in Boston. “It’s almost mythical. All the other species, for at least some part of their lives, actually require wood.”
The species, called Lithoredo abatanica, as essentially a 6-inch worm living in a toothy clam shell. Their teeth are big and flat, which are great for grinding into stone and contrasting sharply with the saw-toothed smile of its wood chewing cousin.
While the wood-eating variety has a sac-like organ for storing and digesting wood, the rock eater doesn’t have that sac in favor of a much more straightforward approach. They eat rocks and they poop it out in a form of sand.
So after collecting and dissecting some specimens, researchers found that the worms were missing the cecum, an organ in other shipworms that digests wood. Instead, their gut was full of stone fragments, the same type of stone they lived in, and they excreted sandy particles of stone as well. The researchers were able to observe the process by watching some of the creatures in an aquarium.
“There are a small number of animals that do ingest rock — for example, birds use gizzard stones to aid digestion. But Lithoredo abatanica is the only known animal that eats rock through burrowing,” said Shipway.
The differences between abatanica and other shipworms means it likely split off from an ancestor of traditional shipworms long ago, and this species is apparently not closely related to its wood-eating brethren.
So why eat rocks and poop sand?
Scientists believe that these creatures do have an impact on the course that rivers take. They’re able to turn rocks into sand, so researchers theorized they could redirect rivers with potentially disastrous results.
Some of that stone is eventually transformed into a protective burrow for the animal. And when the shipworm abandons its home, crabs and shrimp are happy to move in.
Now, since they only eat rocks, how do they get nutrition? a rock is about the least useful thing you could put in your mouth. And it’s true, the nutritional value of a rock remains zero. That also applies, researchers suggest, to the rock-eating shipworm. Other than that, they’re also confused about the chonky size of these worms.
Wood-eating shipworms keep a little symbiotic bacteria around their gills to help them digest wood. But scientists have yet to determine what kind of bacteria a rock eater needs to get its dinner down. It may be something completely new that’s derived from bedrock at the bottom of rivers, a compound that could someday propel advances in human medicine such as antibiotics.
The team said that they hope to soon sequence the strange worm’s DNA to understand how its metabolism works, and they especially hope to learn more about the symbiotic bacteria in their gills.
Shipway said, “We know from previous shipworms that the symbiosis is really important for the nutrition of the animal. We’re going to be examining the symbiosis really closely for further clues about how they get their food.”
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Head or tail?
Everything is still relatively new about this rock eating worm that if we’re to stumble upon one, we’ll wonder which side is the head and which one is the tail. Well, nothing is ever simple with worms. One—a marine worm that lives off the coast of Scotland—has a pair of eyes on its butt.
Brandon Specktor at LiveScience reports that the Scottish worm was spotted during a survey of an unexplored area of the West Shetland Shelf Marine Protected Area to the north of Scotland. In sand pulled from the seafloor just 400 feet below the surface, researchers found 80 of the new quarter-inch-long worms. Most of the marine worm’s body wasn’t particularly unusual.
There was something peculiar about its rear end. They discovered it has a pair of little tentacles sprouting from its rump, with beady little black eye at the end of each stalk.
So why does this species, called Ampharete oculicirrata have eyes on its bum? Specktor reports that’s not unusual for marine worms to have eyes both on their head and other places on their bodies to keep tabs on predators while they search for dinner on the seafloor. Finding eyes on their butt, however, is unusual.
The worm is an excellent case study in showing just how little we know about the seafloor. “The fact that it was found in relatively shallow depths, relatively close to the Scottish coastline, shows just how much more there is to understand about the creatures that live in our waters,” said Jessica Taylor, marine evidence advisor for the United Kingdom’s Joint Nature Conservation Committee.