THE SHIP WORM FAMILY TEREDIDAE. Genus TEREDO, Linn.
The Ship Worm (T. navalis, Linn.) has long been known and dreaded as the treacherous destroyer of ships and wharves, which damages shipping in European and American ports contin uously. Modern scientific researches have uncovered the methods of this mollusk, and devised a preventive of depredations from it.
The life history is most interesting. There is a brief, free swimming period, during which the infant borer has eyes, which disappear in later life. When the size of a pin head, the young settle on the surface of submerged timbers. They begin to bur row inside, cutting off fine chips with the foot, possibly also by scraping with the valves. The burrow gradually grows in diameter and length, the siphon tips always at the small exit, the shells at the extreme end of the excavation. The burrow follows the grain where convenient, avoiding knots by changing direction, and turning aside usually for the burrows of others, though any bur rowed wood specimen shows numerous exceptions to this rule.
The fine chips are swallowed and thrown out of the excurrent siphon, but this does not prove that they yield any sustenance to the mollusk. The large incurrent siphon, ciliated at the mouth, admits a steady stream of water charged with fresh air to bathe the gills; the lashing cilia drive in also minute organisms like infusorians which are passed into the stomach. This supply of food is quite sufficient. Moreover, the wood particles ejected seem only compressed, in no sense changed in composition or structure by digestive processes.
The Teredo breeds in spring. Millions of eggs are said to 312 The Ship Worm be expelled by one female. The young are free-swimming for a week or two. When the size of a pinhead they settle on a floating tree or timber, tree roots, a ship's bottom, piles of bridges, or wharfing — any wood surface soaked in sea water is suitable to harbour them, provided it is not especially "medicated" to discourage their colonising it.
The tiny hole the Teredo makes to enter is never enlarged, though the burrow widens as it lengthens behind it. Only the slender tips of the siphons are extruded, imbibing and excreting organs. These are also sensitive tentacles. Back from their tips they are bound together, and two shelly valves, called pal lets, or claustra, are hinged to the muscular wall. Pick up a bit of floating wood in New York harbour or elsewhere, and you are likely to cause a sparse fringe of colourless siphons to be suddenly retracted. The surface shows only inconspicuous pinholes. Cut
into the wood, and it is honeycombed with tubes. Long, worm like bodies inhabit shell-lined burrows. The pallets have sprung forward to cover the tips of the retracted siphons, and form a door barring the entrance effectually.
The pallets, by compressing and relaxing the walls of the siphons, help to pump water through the long canal. Perhaps they help to excavate the sides of the burrow after the foot had done the first hard digging. Possibly the valves of the shell assist. The problem is unsolved as yet. The shelly lining of the burrow is deposited by the mantle.
The shipping of the world has been at the mercy of this hardy little devastator, until metal sheathing and creosote oil were applied to submerged surfaces of wood. Uncounted methods were tried before success was reached. Ships' bottoms crumbled before a sign showed the timbers to be infested with the worm. Piles of bridges and wharves snapped below the water line for like reasons.
The ship worm does not like the taste of creosote, so painting with this, or better, soaking timbers in the oil or forcing it into the fibre by pressure, insures the preservation and defence of the wood against decay and ship worms. 1 t is a double advantage to use it. Unprotected wood is rarely used in wharf and ship building. Driving copper nails into timbers discourages the Teredo, but it is not a thorough method. There are still unguarded areas where rot and the borer may enter, and work at the heart.
313 The Ship Worm In temperate waters T. navalis is about six inches long, when full grown. In the tropics it is often two feet long. Ordinarily the shell itself is never larger than a small hazel nut; the pallets grow to two inches in length. There is a related mollusk, Kuphus arenarius, Linn., living in sands in the Philippines, which has a tube two yards long, somewhat like the watering-pot's trum pet-like spout.
A boring isopod, Limnoria lignorum, shares with the Teredo the blame for destroying wood exposed to sea water. This crea ture actually swallows its chips. It subsists upon wood. Teredo feeds upon microscopic organisms taken through the incurrent siphon from the water. It asks lodging, but not board, too; so it asks less than Limnoria does.
A good word for Teredo navalis. It clears harbours of wooden debris; the hulks of derelicts, floating and sunken timbers, up rooted and drifting trees, all of them hidden dangers to naviga tion, until they crumble as the result of the perforation of their fibres by the ship worm. It is a scavenger of sea coasts.