Wooden vessels may support an additional sort 

 of marine organisms — animals that actually burrow 

 into the hull. Shipworms (or teredos), which are 

 the principal type of this class, are true Mol- 

 lusks. At the far end of their shell— lined tun- 

 nels, the typical forms have a clamlike shell 

 "which is far too small to contain the long worm- 

 like body, and is used as a cutting instrument to 

 lengthen the curved and twisted burrow. As the 

 entrance to each tunnel at the surface of the 

 hull is relatively small, the extensive damage 

 caused by shipworms is often overlooked. 



A second type of animals that burrow in wooden 

 hulls is represented by the Gribble ( Limnor ia 

 I ignoruui) . This is a small crustacean, 1/8 to 

 1/4 of an inch long, that looks like a tiny sow- 

 bug or woodlouse. It gnaws interlacing burrows 

 in the surface of the wood. As it is often very 

 abundctnt, the outer layers of an unprotected hull 

 may be speedily destroyed. 



