Shipworm

Shipworm
Teredo sp.
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Bivalvia (or Pelecypoda)
Order:	Myoida
Family:	Teredinidae Rafinesque, 1815
Genera
See text

Shipworms are not worms at all, but rather a group of unusual saltwater clams with very small shells, notorious for boring into (and eventually destroying) wooden structures that are immersed in sea water, such as piers, docks and wooden ships. Sometimes called "termites of the sea", they are marine bivalve molluscs (Eulamellibranchiata) in the family Teredinidae, also often known as Teredo worms.

Description

When shipworms bore into submerged wood, bacteria (Teredinibacter turnerae strain ATCC 39867 / T7901) in a special organ called the gland of Deshayes allow them to digest cellulose. The excavated burrow is usually lined with a calcareous tube. Shipworms have slender worm-like forms, but nonetheless possess the characteristic structures of bivalves. The valves of the shell of shipworms are small separate parts located at the anterior end of the worm, used for excavating the burrow.

The shipworms belong to 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.

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 were 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 dykes had to be faced with stones. Teredo has recently caused several minor collapses along the Hudson River waterfront in Hoboken, New Jersey, due to damage of underwater pilings.

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.

Engineering inspiration

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, the behaviour and anatomy of the shipworm inspired the French engineer Marc Brunel, the father of the famous British engineer Isambard Brunel. Based on his observations of how the shipworm's valves simultaneously enable it to tunnel through wood and protect it from being crushed by the swelling timber, Brunel designed an ingenious modular iron tunnelling framework—a tunnelling shield—which enabled workers to tunnel successfully through the highly unstable river bed beneath the Thames. The Thames Tunnel was the first successful large tunnel ever 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".

Culinary delicacy

In Palawan and Aklan in the Philippines, the shipworm is called tamilok and is eaten as a delicacy there. It is prepared as kinilaw—that is, raw (cleaned) but marinaded 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.

Genera

Genera within the family Teridinidae include:

• Bactronophorus Tapparone-Canefri, 1877
• Bankia Gray, 1842
• Dicyathifer Iredale, 1932
• Kuphus Guettard, 1770
• Lyrodus Binney, 1870
• Nausitoria Wright, 1884
• Neoteredo Bartsch, 1920
• Nototeredo Bartsch, 1923
• Psiloteredo Bartsch, 1922
• Spathoteredo Moll, 1928
• Teredo Linnaeus, 1758
• Teredora Bartsch, 1921
• Teredothyra Bartsch, 1921
• Uperotus Guettard, 1770

See also

• Gribble
• Bug shoe

Further reading

• "Teredinidae". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=81832. 
• Powell A. W. B., New Zealand Mollusca, William Collins Publishers Ltd, Auckland, New Zealand 1979 ISBN 0-00-216906-1