Eats Rocks, Poops out Sand: Meet the New Species of Shipworms

They are called “shipworms” due to the age-long nuisance they’ve constituted to fishermen and sailors, feeding on moist and rotting wood, causing wooden ships and boats to sink, destroying piers and docks, and literally eating their way through any piece of wood that happens to be in their habitat water. There are over 65 species of these bivalve mollusks in existence, each with its own share of destructive tendencies and capabilities [1].

However, there’s a newly discovered species that has a completely different taste in elements. First discovered in 2006 in the French National Museum of Natural History, the Lithoredo abatanica is a species of shipworms that burrows through hard substances such as stones, rocks, and solid ground, feeding on the rocky particles and excreting gritty sand [2]. They are like the Hercules species of shipworms, so unique that the group of international scientists who discovered them had to create a whole new genus to classify these organisms. 

Exploring the rock-borers

Following the first exposition in 2006, they were studied extensively in 2016 at the Abatan River in Easter Bohol, The Philippines. “Litho” stands for rock, and “Teredo” is the family to which shipworms belong. “abatanica”, in honor of the river where they made their first known natural habitat, currently the only place in the world where the Lithoredo have been found. They were found burrowed deeply in carbonate limestone bedrocks in the freshwater river, tearing through the natural ecosystem in perfect tunnels.

A study published in the Proceedings of the Royal Society B. last month explained that these mollusks may be the next major agents of natural weathering, chipping away at river banks and borders, possibly aiding the effects of rushing water and distorting nature’s laid-out plans.  They may also be able to survive on damp land and carry out a measure of destruction on the natural landscape and terrains.

However, they may not be as destructive as the other shipworm species. According to Reuben Shipway, a marine biologist at the University of Amherst and lead author of the review, the Lithoredo may actually be helpful to other organisms in the natural aquatic ecosystem. “These animals are among the most important in the river and in this ecosystem. As they bore elaborate tunnels in the limestone bedrock, these animals change the course of the river and provide a really rich environment for other aquatic species to live in. So far, this is the only place on earth that we know these animals exist.”

Unique to the Shipworm family

Shipworms are distant relatives of clams and they aren’t exactly worms. They are called worms because they have a similar outer appearance, but they are actually bivalve mollusks that prefer to ingest wood to underwater sediment (xylotrophs) [4]. 

Bivalves are a class of mollusks that are divided from front to back into right and left valves, the class to which oysters, clams, mussels, and scallops belong. Found mostly in salty and brackish waters, most shipworms chip off wood using abrasive bumps that cover their outer shells, another difference in features that makes the Lithoredo so unique. 

The Lithoredo has brought a whole new world of outstanding research to marine biologists all over the globe. Coming up to about 4 inches in height, although the scientists believe they may be able to stretch up to a meter, these freshwater mollusks are as good a drill-bit as any electrical device you could get your hands on. They may take a longer amount of time, but they’ll definitely get the job done. They don’t merely dig through the rocks on the surface. They live inside these rocks – feeding, excreting, and reproducing. 

How do they process rocky particles into energy?

They feed on rocks and stone by digging through with their shells covered in dozens of tiny teeth rather than abrasives, eating through rocks as hard as limestone in a matter of days. Presently, not very much is known about these shipworms, but the scientists believe that the rocks may not really feed the new species as well as wood feeds their relatives. Symbiotic gill bacteria act upon the wood which most other shipworms ingest, breaking them down into absorbable carbon for energy [5]. 

The Lithoredo, however, would ingest solid rocks and excrete gritty sand from the other end, and there has been no solid evidence that any biochemical actions are performed on these rock molecules as energy conversion. The only difference in forms of the ingested and egested rocks that they are broken down into smaller bits, which leaves one to wonder what exactly these creatures are feeding on.

“Most other shipworms are as skinny as your finger,” Shipway says. “These animals are quite chubby, robust. They look really different. Where they get their nutrition we don’t know.” The researchers used X-ray diffraction analysis to compare the structure of the parent rocks and the excreted sand, and they were basically still the same material with no chemical alterations. 

A newly discovered genus would mean years of research and analysis to better understand the ecological habits and adaptation mechanisms of these organisms. The researchers are eager to figure out exactly how these mollusks can eat rocks and egest excreta of the exact same chemical structure. Perhaps, the bulk of the rocks in their guts may be a sufficient source of chemical energy. 

Anyway, there’s more to be discovered and explored. There is a possibility that medical benefits may arise from studying the unique strains of bacteria in the Lithoredo gills. They may provide a new basis for research on drug-resistant bacteria and antibiotic medications.