Rocks would not be the first choice for a human or animal’s breakfast, but that’s exactly what a newly discovered clam enjoys munching on. It’s a type of shipworm which is a group of clams that eat wood mostly from ships and have “small rows of small, sharp teeth on the shell and a special organ for wood storage and digestion, called the caecum,” explained Reuben Shipway, who is the lead researcher of the study (which can be read here), as well as a postdoctoral researcher at the Marine Science Center at Northeastern University in Massachusetts.
Since every shipworm that’s currently known to researchers eats wood, it was surprising when, in 2018, residents from Bohol province in the Philippines reported a freshwater shipworm that fed on rocks. The rock-eating shipworm is known locally as “antingaw” and it is often eaten by women who believe it will help them lactate for their newborns.
This newly discovered shipworm has been named Lithoredo abatanica which translates to “rock shipworm from the Abatan River”. It has lost all of its previous adaptations for digesting wood, such as the caecum. Instead, its “shell has these really large, shovel-like projections for digging into rock,” stated Shipway.
While the clam eats limestone, it’s still unclear whether it gets any real food from the rocks or if it just feasts on the rocks alone. Shipway explained, “We want to look at the symbionts, the bacteria that live inside these animals, to see if they are providing any nutrition, and this is an area of research we are currently focusing on.”
What’s even more incredible than eating rocks is that it expels it as a fine sand. Shipway went on to say, “There are a small number of animals that do ingest rock – for example, birds use gizzard stones to aid digestion,” adding, “But Lithoredo abatanica is the only known animal that eats rock through burrowing.”
And they are not a typical-looking clam, as they are translucent, plump, and worm-like. While the majority of the specimens gathered by researchers were 4 inches long, some were quite a bit bigger. “When I was diving in the river, I saw burrows that were over 2 feet in length!” Shipway said, adding, “So, there may be some absolute monsters living deep in the rock.”
Other species of fish and crabs can live in the burrows created by the Lithoredo abatanica so this is a pretty important discovery in regards to the freshwater living environments.
You can see a picture of the newly discovered Lithoredo abatanica here as well as some of the burrows it created.