A Bizarre New Species of Mollusk Eats Rocks, Poops Sand, and Shapes Rivers

What eats rock, poops sand, and bores holes in riverbeds? It’s Lithoredo abatanica, a newly discovered species of shipworm that is radically different from its closest relatives.

The bizarre animal demonstrates the diversity of shipworms, an important family of mollusks, and its unique biology may inform the development of new drug treatments, according to a study published on Wednesday in Proceedings of the Royal Society B.

Most shipworms burrow into submerged wood, making them a well-known pest to sailors and dockworkers for thousands of years. But last year, the rock-eating variety was found in the Abatan River of the Philippines by scientists working with the Philippine Mollusk Symbiont International Collaborative Biodiversity Group.

The new study represents the first time that L. abatanica has been formally described and named, but the animal is part of the local culture, where it is known as an “antingaw.”

“It turns out [locals] have known about these animals for ages and they feed them to young mothers to induce lactation,” said lead author Reuben Shipway, a marine biologist at Northeastern University, in a phone call with Motherboard.

Shipworms are considered a delicacy throughout the Philippines, and the special bacteria in their gills could be adapted into antibiotics and other treatments.

“One of the reasons we do this research is to discover novel drug compounds from these animals that could be used for humans,” Shipway said.

After finding and extracting a few specimens from their rocky burrows on the riverbed, about two meters below the surface, Shipway and his colleagues studied them using scanning electron microscopy, micro-computed tomography, and DNA analysis.

The results showed that the organs responsible for wood digestion in all other shipworms were completely absent from L. abatanica. This missing adaptation makes the species the only known shipworm that does not rely on wood, either as food or shelter, for any part of its lifecycle.

The translucent creature, which measures a few inches long, instead uses its shell-like mouth to burrow through limestone. That rock eventually exits its anal canal as sand. The nature of the digestive process that happens in between remains an open question, the study said.

The animal may rely on the bacteria in its gills to feed it, as other shipworms do. It could also be using the rocks to grind down plankton or other microbes for easier digestion, or perhaps it somehow derives sustenance from the rock itself. It will take more research to untangle the mystery of its diet.

Shipway and his colleagues observed crabs, shrimp, limpets, snails, mussels, and bristle worms squatting in the abandoned tunnels created by L. abatanica, suggesting that many other species rely on its rock-munching skills.

The fact that it turns rock into sand is also transforming the bedrock of the river. “Over time, this process will eventually cause the river to change direction,” Shipway said.

The small shipworm exerts such a big influence over its habitat that it is considered a “dominant ecosystem engineer,” the authors concluded.