Shipworms are not worms at all, but bivalve mollusks and closely related to clams. Their shells have been modified into hard plates located near the head of the animal. They feed digging their burrows into driftwood, using their reduced shell as a sort of drill. Before modern iron-hulled ships, they were the nightmare of every sailor, as the appropriately named “shipworms” burrowed also into the wooden planks of sailing ships.
However, in June 2019, a research team described a new species digging its burrows in limestone. Lithoredo abatanica was first spotted in 2006, hiding in thumb-size burrows in the limestone banks of the Abatan River on the Philippine Island of Bohol. But it wasn’t until 2018 that scientists were able to study the organism in detail. The species has a soft, worm-like body, typical for shipworms, and can grow almost three feet in length. The rock-eating shipworm scrapes away the limestone using its modified shell and a series of tiny teeth, ingesting the pulverized rock. Symbiotic bacteria residing in the gills digest the organic material contained in the limestone. The shipworm then absorbs the bacteria’s waste products for nourishment.
Lithoredo abatanica may also play an important role in river systems of the Philippines. The empty burrows provide shelter for crabs, snails and fish. The network of burrows and crevasses caused by the animals digging activity may also influence river dynamics. The cavities in the limestone weaken the rock, making it for the river more easy to erode a new course.