National Geographic : 1956 Oct
560 Robert F. Sisson, National Geographic Staff Pearl-like Head Identifies Shipworm as a Mollusk Voracious cousin of oyster and clam, the teredo can eat its way with ease through most woods. Twin valves armed with microscopic teeth spell ruin for unprotected ships' bottoms and marine timbers. The average adult measures four to six inches. This teredo, magnified four times, is drawn from a test block at the Marine Laboratory of the University of Miami. Dark wedge on the left of the spherical head outlines the mouth. As the invader rasps its way into the wood, it grows rapidly and soon makes a burrow about the width of a pencil or wider, accord ing to the species. But in each case the entrance remains no larger than is necessary for the siphons to project. Thus a boat's planks may seem sound on the outside, even though riddled with worms. When this happens, only one breakthrough at a weak point is necessary to open up an extensive leak and perhaps sink the craft. To combat the shipworm, it is necessary to know how it operates; so scientists at Miami have been watching the way in which the little creature enters the wood. holes in wood for phrase Ogden Nasi Biologist Don Menker, for instance, may dip some of the larvae from a breeding tank and ob serve them under the mi croscope as they swim in sea water. At this stage the shipworm is roughly spherical and has two deli cate transparent shells, which cover most of the body. Baby Stops Swimming, Attacks Wood Gradually giving up its free-swimming career, the baby begins to glide or crawl on wooden surfaces by means of its foot, a long projection like that of a snail. The tip of the waving fingerlike foot seems to seek out a good spot on the wood. Before long the infant shipworm begins to burrow straight down into the wood, the foot becomes smaller, and, as the burrow progresses, the body lengthens into the adult form. From now on the burrow parallels the surface of the wood. Looking at the larva, one can envisage the evo lution of shipworms from a clamlike ancestor, which, from simply bur rowing in mud or sand, began to make shallow its protection. To para h: Some primal shipworm found some wood, And tasted it and found it good. That is why your cousin May Fell with the dock in the sea today!* There are many different species of ship worms throughout the world. Most of them can survive only in sea water. This accounted for a second period of wharf collapse near San Francisco. * See Good Intentions, by Ogden Nash, Little, Brown and Company, © 1942 by Ogden Nash.