Recent Discovery of Giant Shipworm Kuphus polythalamia's Unique Feeding Strategy

Kuphus polythalamia is a type of bivalve called a "shipworm" (although K. polythalamia is not a worm, nor does it live on a ship).  It is a member of the family Teredinidae. Shipworms are elongate, and have rasp-like shells for burrowing into wood. Kuphus polythalamia is unusual because of its large size.  It can reach up to five feet long and grow to almost two and a half inches in diameter.

Kuphus polythalamia  has been known of for a long time, due to the frequent discovery of their elephant tusk-like shells since the 1700s. However, the animal itself was usually long since dead and decomposed and had never been studied. Since its shells were usually dragged up in nets by fishermen, it was hard for scientists to pinpoint the exact habitat where it lived. By chance, a documentary filmed in the Phillipines showed it burrowed into the sediment of a lagoon. A team of scientists launched an expedition to that location, and brought back specimens.

They found that, unlike other shipworms, which feed on wood, which they are able to digest because of symbiotic bacteria that produce digestive enzymes to break down the wood (allowing the bacteria, in return, to obtain organic carbon from their shipworm host), Kuphus polythalamia does not eat wood.  Its digestive organs have shrunk, and it spends most of its time encased in its closed up shell, without taking in any wood.  Instead, it relies on a chemotrophic feeding strategy, meaning that it metabolises chemicals instead of sunlight (autotrophs) or organic matter (heterotrophs). Most shipworms are heterotrophic.

The way this works for Kuphus polythalamia is that it has bacteria, which live in its gills, and  metabolize sulfur. In doing this, the bacteria create organic carbon, which Kuphus polythalamia feeds on.  This is the different from the usual shipworm mutualistic symbiotic relationship.  Kuphus polythalamia's symbiotic partner bacteria do not rely on it for food.  Instead, they provide it with food by breaking down sulfur based environmental compounds that come from rotting wood in the area.  (The lagoon where Kuphus polythalamia was found had been used as a log storage pond.)

It has been hypothesized that the way this trait evolved was that Kuphus polythalamia's ancestors fed on wood, specifically wet, rotting wood, which released sulfur. They shared the enviroment with chemotrophic bacteria, and somehow, the chemotrophic bacteria got stuck in their gills. Instead of dying, the bacteria thrived, and as a byproduct of their chemosynthesis, they manufactured organic carbon, which is benificial for shipworms. This feature allowed these individuals to survive better than those without the bacteria, and for them to exploit new habitats, such as the muddy bottom of a lagoon. Eventually, they evolved into a seperate species, Kuphus polythalamia.

SOURCES:

Kuphus polythalamia: Marine Biologists Study Giant Mud-Dwelling Shipworm for First Time, Science News (April 18 2017.) Published online at    http://www.sci-news.com/biology/kuphus-polythalamia-giant-mud-dwelling-shipworm-04789.html?fbclid=IwAR3fxZweBBuujpO6eO3emt3xxHqrLv3UtBP_nfTLPibCF04NhBn_oTDmis8

Kish, Stacy W., Science Fiction Horror Wriggles Into Reality with Discovery of Giant Sulfur-Powered Shipworm (April 17 2017.)  Published online at https://healthcare.utah.edu/publicaffairs/news/2017/04/shipworm.php?fbclid=IwAR2ZHz1Ugxpz05o5Kxv0SwF_HRYYoCe0USWL3t_FvB66SbEGGN7MV1HsSH4

Daniel L. Distel, Marvin A. Altamia, et al, Discovery of Chemoautotrophic Symbiosis in the Giant Shipworm Kuphus polythalamia (Bivalvia: Teredinidae) Extends Wooden-Steps Theory, Proceedings of the National Academy of Sciences Apr 2017, 201620470.  Published online at https://www.pnas.org/content/early/2017/04/13/1620470114.full