Custom Search
|
|
|
||
 4.4.1 Mollusca.
4.4.1.1 Teredo. Teredo, also called shipworms or Teredinids, have a worm-like
appearance. They are notorious for causing extensive damage to wooden ships and other wooden
waterfront structures. Surface damage is minimal, but once inside a wood member, it can be com-
pletely honeycombed (Figure 4-32) in a short time period.
Teredo reproduce from eggs which are fertilized within the female. The eggs develop into micro-
scopic free-swimming larvae which are able to move about in the water or over the surface of sub-
merged wood in search of suitable new locations to begin boring.
Boring is done by the mechanical rasping action of a pair of shell-hardened valves equipped with
fine teeth on the head of the animal. The wood is partially digested to supplement the food fur-
nished by other organisms. The posterior of the body has two siphons which extend into the water.
The incurrent siphon draws in water containing microscopic organisms for food and dissolved
oxygen for respiration. The excurrent siphon expels waste products.
An entrance hole about 1/16 inch in diameter is bored into the surface of the wood by the young lar-
vae. Thus, it is difficult to detect their presence or extent of damage from the surface of the wood.
Attack is frequently concentrated at the mud line. The larvae enter the wood at right angles to the
grain and then burrow with the wood grain in the longitudinal direction, following a very irregular
course, turning to avoid unfavorable sections such as knots. Once inside the wood, the larvae
develop wormlike bodies rapidly and remain imprisoned in the wood for life. Adults may be one to
two feet in length and one-half inch in diameter. The wall of the hole is lined with a shell-like (cal-
careous) deposit. When the animal's siphons are withdrawn from the water into the hole, the open-
ing is plugged with small calcareous pallets. These borers may completely honeycomb a piece of
wood, yet the surface will show only slight damage due to the small entrance holes.
Shipworms are found in all coastal waters of the United States. Teredo are capable of withstanding
broad changes in salinity, thus they can also be found in the upper reaches of many estuaries.
Shipworms are deterred by preservative treatments of 20 to 25 pounds of marine-grade creosote
meeting AWPA Standard P13-85 or creosote-coal tar meeting AWPA Standard P12-85 per cubic
foot of wood, or 2.5 pounds of ACA or CCA per cubic foot of wood.
4.4.1.2 Bankia. Bankia are very similar to Teredo with a few exceptions. First,
in their life cycle, the egg is ejected into the water and fertilized there. Larvae capable of swimming
develop within a few hours, but they do not attack the wood for approximately one month. The
adults may be up to five or six feet long and 7/8 inch in diameter.
4-53
|
 
|
|
|
||
