A worm-like creature that grows to almost two metres long, lives in stinking mud and doesn’t eat a thing is shedding new light on evolution and the nature of co-dependence.
Described in Proceedings of the National Academy of Sciences, the giant shipworm (Kuphus polythalamia) has been found alive for the first time, after a scientist saw it in a wildlife documentary aired on Philippines television and realised it was a species unknown to science.
In one sense, Kuphus polythalamia has been known for centuries, because the characteristic long empty shells it leaves behind have often been collected by fisherfolk and travellers.
However, no one had ever seen a live specimen, much less discovered where it lived or what it ate.
The answer to the first question, it turns out, is remote lagoons filled with rotting wood and deep, sucking mud that emits large amounts of hydrogen sulfide – often called, for good reason, rotten-egg gas.
And the answer to the second question seems to be nothing at all – and it is at this point that a mollusc almost as tall as a basketball player gets even more interesting.
A team of researchers led by Daniel Distel of Northeastern University in Massachusetts, US, discovered that the shipworms harbor in their gills colonies of bacteria that survive by digesting the hydrogen sulfide – a type of consumption known as chemosynthesis.
Chemosynthetic bacteria are not uncommon. They colonise many environments where sunlight is absent, ranging from deep-sea hydrothermal vents to animal corpses and rotting plant matter. While some derive energy from rotteneegg gas, others process ammonia, molecular hydrogen, ferrous iron or sulfur.
In processing the hydrogen sulfide, the bacteria in Kuphus polythalamia gills produce organic carbon that provides its nourishment. That this has been a very long-term symbiosis is evidenced by the fact that many of the shipworm’s internal digestive organs have atrophied.
The discovery of the living giants provides welcome support for Distel, who has been studying the shipworm family, Teredinidae, for decades.
All other types of shipworm are comparatively small, and live exclusively in rotting wood. Some 20 years ago Distel suggested that other species would need to strike up intimate relationships with chemosynths in order to colonise less narrow environments.
In Kuphus polythalamia he appears to have found proof, and perhaps the first of many examples.
“We are also interested to see if similar transitions can be found for other animals that live in unique habitats around the world,” he says.