UP’s discovery of the rare giant shipworm and the mystery it solved

For centuries, the giant shipworm remained an enigmatic bivalve species–until scientists, including those from the University of the Philippines Marine Science Institute, recently found a group of it burrowed in the black marine sediments of Sultan Kudarat, southern Philippines.

Named Kuphus polythalamia, the rare animal belongs to the common wood-boring, wood-feeding bivalve family Teredinidae. The family is composed of clams with long, soft bodies such as the tamiloks of Palawan and Aklan.

But the giant shipworm stands out from the rest of its kind.

First of all, it has an unusual body that may grow up to 155 cm in length and 6 cm in diameter, the greatest length of any existing bivalve.

Second, its adult specimens bore into marine sediments instead of wood.

The discovery was first reported in the Proceedings of the Natural Academy of Sciences by the researchers from the University of the Philippines and their collaborators from Northeastern University, University of Utah, Second Genome, École Normale Supérieure, Sultan Kudarat State University and Drexel University.

Comparative anatomy and life position of Kuphus polythalamia and Lyrodus pedicellatus (Source: Distel et al. in PNAS)

According to their paper, chemosynthetic symbioses give certain marine invertebrates the unusual ability to consume inorganic chemicals such as hydrogen sulfide rather than organic matter as food.

Animals of this type are found near geochemical sources of hydrogen sulfide on the seafloor such as hydrothermal vents or near biological sources like decaying wood or large animal carcasses.

However, while many such symbioses have been known to scientists, there is very little information as to how or where they began. This is because of the absence of live specimens that can be studied.

With the discovery of the giant shipworm, scientists were then able to look at a new chemosynthetic symbiosis and show how it originated in a wood-eating ancestor where “wood served as an evolutionary stepping stone for a dramatic transition from heterotrophy to chemoautotrophy.” In other words, from depending on organic substances for nutrition, the organism changed into one that derived energy from inorganic chemical compounds.

“Clearly, an organism’s biology is influenced not only by its bioecology (that is, other organisms that live in a habitat) but also by its geophysicochemical ecology,” said Dr. Gisela P. Concepcion, head of the Marine Natural Products Lab (MNPL) which was part of the breakthrough research.

“The site where the giants were found had thick, muddy, anoxic water with lots of degrading wood, rich in hydrogen sulfide. We were told by the local folk that there used to be a lumber mill and a thick wooded area near the site. Then sometime back, a lot of the trees fell on the site because of a typhoon and a runoff,” Concepcion added.

MNLP has been studying small tamiloks and their wood-digesting symbiont bacteria since 2009. It has been working with foreign collaborators under the Philippine Mollusk Symbiont International Cooperative Biodiversity Group funded by the Fogarty International Center-National Institutes of Health.

Concepcion described the discovery as “a scientifically exhilarating and rewarding journey,” to unravel “one of the deep secrets of marine evolutionary biology.”

Last edited: 27 April 2017