Shipworms, termites of the sea

March 13, 2023
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This dried specimen of Teredo navalis, and the calcareous tunnel that originally surrounded it and curled into a circle during preservation, were extracted from the wood of a ship. The two valves of the shell are the white structures at the anterior end; they are used to dig the tunnel in the wood.

The shipworms are marine bivalve molluscs in the family Teredinidae: a group of saltwater clams with long, soft, naked bodies. They are notorious for boring into (and commonly eventually destroying) wood that is immersed in sea water, including such structures as wooden piers, docks and ships; they drill passages by means of a pair of very small shells (“valves”) borne at one end, with which they rasp their way through. Sometimes called “termites of the sea”, they also are known as “Teredo worms” or simply Teredo (from Ancient Greek: τερηδών, romanized: terēdṓn, lit. ‘wood-worm’ via Latin: terēdō). Carl Linnaeus assigned the common name Teredo to the best-known genus of shipworms in the 10th edition of his taxonomic magnum opus, Systema Naturæ (1758).

The tunneling habit of species in the genus inspired the name of the Teredo network tunneling protocol. The submarine HMS Teredo may also have been named after this genus, which works invisibly, below the surface, and can be very damaging to marine installations made of wood.

Description

Teredo navalis from Popular Science Monthly, September 1878

Removed from its burrow, the fully grown teredo ranges from several centimetres to about a metre in length, depending on the species. The body is cylindrical, slender, naked and superficially vermiform, meaning “worm-shaped”. In spite of their slender, worm-like forms, shipworms possess the characteristic morphology of bivalves. The ctinidia lie mainly within the branchial siphon, through which the animal pumps the water that passes over the gills.

The two siphons are very long and protrude from the posterior end of the animal. Where they leave the end of the main part of the body, the siphons pass between a pair of calcareous plates called pallets. If the animal is alarmed, it withdraws the siphons and the pallets protectively block the opening of the tunnel.

The pallets are not to be confused with the two valves of the main shell, which are at the anterior end of the animal. Because they are the organs that the animal applies to boring its tunnel, they generally are located at the tunnel’s end. They are borne on the slightly thickened, muscular anterior end of the cylindrical body and they are roughly triangular in shape and markedly concave on their interior surfaces. The outer surfaces are convex and in most species are deeply sculpted into sharp grinding surfaces with which the animals bore their way through the wood or similar medium in which they live and feed. The valves of shipworms are separated and the aperture of the mantle lies between them. The small “foot” (corresponding to the foot of a clam) can protrude through the aperture.

The shipworm lives in waters with oceanic salinity. Accordingly, it is rare in the brackish Baltic Sea, where wooden shipwrecks are preserved for much longer than in the oceans.

The range of various species has changed over time based on human activity. Many waters in developed countries that had been plagued by shipworms were cleared of them by pollution from the Industrial Revolution and the modern era; as environmental regulation led to cleaner waters, shipworms have returned. Climate change has also changed the range of species; some once found only in warmer and more salty waters like the Caribbean have established habitats in the Mediterranean.

Kuphus polythalamia

Kuphus is a genus of shipworms, marine bivalve molluscs in the family Teredinidae. While there are four extinct species in the genus, the only extant species is Kuphus polythalamius (also incorrectly spelled as Kuphus polythalamia). It is the longest bivalve mollusc in the world, where the only known permanent natural habitat is Kalamansig, Sultan Kudarat in the Philippines.

Members of this genus secrete calcareous tubes. Based only on the calcareous tube, this species was originally thought by Linnaeus to be a tube worm, so he placed it in the genus Serpula. Despite the fact that Kuphus polythalamius is now known to be a mollusc, its common name is the giant tube worm. Since 1981 however, the name “giant tube worm” has also been applied to the hydrothermal vent species Riftia pachyptila, which is indeed a worm, an annelid.

Misidentification as dinosaur remains

Fossils found near Warsaw by paleontologist, Friedrich von Huene in 1941 were misidentified as being the teeth and parts of the jaw of a new species of dinosaur, which he named Succinodon putzeri. It was later determined that these were in fact the fossil remains of a marine boring bivalve, a previously undescribed species of Kuphus.

The longest marine bivalve, Kuphus polythalamia, was found from a lagoon near Mindanao island in the southeastern part of the Philippines, which belongs to the same group of mussels and clams. The existence of huge mollusks was established for centuries and studied by the scientists, based on the shells they left behind that were the size of baseball bats (length 1.5 meters (5 ft.), diameter 6 cm (2.3 in.) ). The bivalve is a rare creature that spends its life inside an elephant tusk-like hard shell made of calcium carbonate. It has a protective cap over its head which it reabsorbs to burrow into the mud for food. The case of the shipworm is not just the home of the black slimy worm. Instead, it acts as the primary source of nourishment in a non-traditional way.

K. polythalamia sifts mud and sediment with its gills. Most shipworms are relatively smaller and feed on rotten wood. This shipworm instead relies on a beneficial symbiotic bacteria living in its gills. The bacteria use the hydrogen sulfide for energy to produce organic compounds that in turn feed the shipworms, similar to the process of photosynthesis used by green plants to convert the carbon dioxide in the air into simple carbon compounds.

Scientists found that K. polythalamia cooperates with different bacteria than other shipworms, which could be the reason why it evolved from consuming rotten wood to living on hydrogen sulfide in the mud. The internal organs of the shipworm have shrunk from lack of use over the course of its evolution[citation needed] The scientists are planning to study the microbes found in the single gill of K. polythalamia to find a new possible antimicrobial substance.

A Wikipedia page about submerged forests says: Submerged forests host a whole variety of flora and fauna. The submerged forest located off of the coast of Alabama near Dauphin Island has the bald cypress tree (Taxodium distichum). Mantis shrimp, crabs, anemones, grouper, and red snappers are commonly found at this submerged forest, and of particular interest, due to their practical use in drug discovery, are shipworms.

Lithoredo 

Lithoredo is a genus of shipworm native to the Abatan River in the Philippines. It contains a single species, Lithoredo abatanica, described in June 2019. The species is unusual because, unlike other shipworms which mainly bore into wood, it tunnels into and excretes limestone. It lacks the cecum which in other shipworms holds symbiotic bacteria which digest wood. Compared to other shipworms, lithoredo have differently shaped teeth which can finely grind stone. The worms use the tunnels to live in but their method of eating is not yet known. They may get nutrition from bacteria in their gills.

Biology

When shipworms bore into submerged wood, bacteria (Teredinibacter turnerae), in a special organ called the gland of Deshayes, digest the cellulose exposed in the fine particles created by the excavation. The excavated burrow is usually lined with a calcareous tube. The valves of the shell of shipworms are small separate parts located at the anterior end of the worm, used for excavating the burrow.

Diet

Teredo worms primarily live by filter feeding. They do not need wood to survive. In this photo we see damage to a non-wooden vessel that appears to have been caused by teredo worms living in casings attached to the outside of the hull. The remnants of a casing appears to be in the bottom right. The vessel was in Langkawi Malaysia. The holes do not appear to be very deep and the worms did not penetrate past the layers of epoxy and epoxy soaked fiberglass. It is thought that an organic filler material may have been used within the epoxy to make it easier to sand. Had the teredo worms made it past the layers of epoxy and fiberglass they would have made it into a wooden core and damage would have been extensive. (Philip Maise)

Like most marine based bivalves, teredo worms are primarily filter feeders and consume mostly seston, and not wood. Wood supplements their primary diet and is consumed with the assistance of bacteria inside their [gill] cells. However, wood is not a necessary part of their diet and they can live on the surface both of wooden and non-wooden structures.

Taxonomy

Shipworms are marine animals in the phylum Mollusca, order Bivalvia, family Teredinidae. They were included in the now obsolete order Eulamellibranchiata, in which many documents still place them.

  • Ponder, Winston F.; Lindberg, David R., eds. (2008). Phylogeny and Evolution of the Mollusca. University of California Press. ISBN 978-0-520-25092-5.

Ruth Turner of Harvard University was the leading 20th century expert on the Teredinidae; she published a detailed monograph on the family, the 1966 volume “A Survey and Illustrated Catalogue of the Teredinidae” published by the Museum of Comparative Zoology. More recently, the endosymbionts that are found in the gills have been subject to study the bioconversion of cellulose for fuel energy research.

Genera

Shipworm species comprise several genera, of which Teredo is the most commonly mentioned. The best known species is Teredo navalis. Historically, Teredo concentrations in the Caribbean Sea have been substantially higher than in most other salt water bodies.

Genera within the family Teridinidae include:

Engineering concerns

Shipworms greatly damage wooden hulls and marine piling, and have been the subject of much study to find methods to avoid their attacks. Copper sheathing was used on wooden ships in the latter 18th century and afterwards, as a method of preventing damage by “teredo worms”. The first historically documented use of copper sheathing was experiments held by the British Royal Navy with HMS Alarm, which was coppered in 1761 and thoroughly inspected after a two-year cruise. In a letter from the Navy Board to the Admiralty dated 31 August 1763 it was written “that so long as copper plates can be kept upon the bottom, the planks will be thereby entirely secured from the effects of the worm.”

In the Netherlands the shipworm caused a crisis in the 18th century by attacking the timber that faced the sea dikes. After that the dikes had to be faced with stones. In 2009, Teredo have caused several minor collapses along the Hudson River waterfront in Hoboken, New Jersey, due to damage to underwater pilings.

Engineering

Teredolites borings in a modern wharf piling. The US one cent coin in the lower left of this image is 19 mm across.

In the early 19th century, engineer Marc Brunel observed that the shipworm’s valves simultaneously enabled it to tunnel through wood and protected it from being crushed by the swelling timber. With that idea, he designed the first tunnelling shield, a modular iron tunnelling framework which enabled workers to tunnel through the unstable riverbed beneath the Thames. The Thames Tunnel was the first successful large tunnel built under a navigable river.

Literature

Henry David Thoreau‘s poem “Though All the Fates” pays homage to “New England’s worm” which, in the poem, infests the hull of “[t]he vessel, though her masts be firm”. In time, no matter what the ship carries or where she sails, the shipworm “her hulk shall bore,/[a]nd sink her in the Indian seas”.

The hull of the ship wrecked by a whale, inspiring Moby Dick, had been weakened by shipworms.

In the Norse Saga of Erik the Red, Bjarni Herjólfsson, said to be the first European to discover the Americas, had his ship drift into the Irish Sea where it was eaten up by shipworms. He allowed half the crew to escape in a smaller boat covered in seal tar, while he stayed behind to drown with his men.

Cuisine

Shipworm as tamilok

In Palawan and Aklan in the Philippines, the shipworm is called tamilok and is eaten as a delicacy. It is prepared as kinilaw—that is, raw (cleaned) but marinated with vinegar or lime juice, chopped chili peppers and onions, a process very similar to ceviche. The taste of the flesh has been compared to a wide variety of foods, from milk to oysters. Similarly, the delicacy is harvested, sold, and eaten from those taken by local natives in the mangrove forests of West Papua, Indonesia and the central coastal peninsular regions of Thailand near Ko Phra Thong.

See also

References

  1. Garcia, Sierra (2021-12-24). “How “Termites of the Sea” Have Shaped Maritime Technology”. JSTOR Daily. Retrieved 2022-05-01.
  2. “Historic shipwrecks could be preserved in the Antarctic”. sciencenordic.com. Retrieved 2017-02-28.
  3. Gilman, Sarah (December 5, 2016). “How a Ship-Sinking Clam Conquered the Ocean”. Smithsonian.
  4. “This Is a Giant Shipworm. You May Wish It Had Stayed In Its Tube. – T…”. The New York Times. 2020-11-15. Archived from the original on 2020-11-15.
  5. Live example seen on 19 April 2017 on the BBC’s website.
  6. Distel, D. L.; Morrill, W.; MacLaren-Toussaint, N.; Franks, D.; Waterbury, J. (2002). “Teredinibacter turnerae gen. nov., sp. nov., a dinitrogen-fixing, cellulolytic, endosymbiotic gamma-proteobacterium isolated from the gills of wood-boring molluscs (Bivalvia: Teredinidae)”. International Journal of Systematic and Evolutionary Microbiology. 52 (6): 2261–2269. doi:10.1099/ijs.0.02184-0. hdl:1912/110. ISSN 1466-5026.
  7. Ponder, Winston F.; Lindberg, David R., eds. (2008). Phylogeny and Evolution of the Mollusca. University of California Press. ISBN 978-0-520-25092-5.
  8. Yang, JC; Madupu, R; Durkin, AS; Ekborg, NA; Pedamallu, CS; Hostetler, JB; Radune, D; Toms, BS; Henrissat, B; Coutinho, PM; Schwarz, S; Field, L; Trindade-Silva, AE; Soares, CA; Elshahawi, S; Hanora, A; Schmidt, EW; Haygood, MG; Posfai, J; Benner, J; Madinger, C; Nove, J; Anton, B; Chaudhary, K; Foster, J; Holman, A; Kumar, S; Lessard, PA; Luyten, YA; Slatko, B; Wood, N; Wu, B; Teplitski, M; Mougous, JD; Ward, N; Eisen, JA; Badger, JH; Distel, DL (Jul 1, 2009). “The complete genome of Teredinibacter turnerae T7901: an intracellular endosymbiont of marine wood-boring bivalves (shipworms)”. PLOS ONE. 4 (7): e6085. Bibcode:2009PLoSO…4.6085Y. doi:10.1371/journal.pone.0006085. PMC 2699552. PMID 19568419.
  9. Bouchet, P. (2015). “Teredinidae Rafinesque, 1815”. WoRMS. World Register of Marine Species. Retrieved 2015-02-14.
  10. “Pier-eating monsters: Termites of the sea causing piers to collapse”. Hudson Reporter. Retrieved 2009-09-29.
  11. “Thames Tunnel Construction”. Brunel Museum. Archived from the original on 2008-06-14. Retrieved 2008-08-31.
  12. Henry D. Thoreau, “Though All the Fates“.
  13. “The Saga of Erik the Red – Icelandic Saga Database”. Icelandic Saga Database. Retrieved 2017-07-04.
  14. Jodelen O. Ortiz (May 2, 2007). “Tamilok A Palawan: Delicacy”. Archived from the original on April 17, 2009. Retrieved 2009-04-30.

Further reading

External links

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