The European Pileworm, a Dangerous Marine Borer .5 



part of the animal is naked, and since it cannot pull its entire body 

 within its shell as does the ordinary clam, it finds protection in its 

 burrow from the attacks of fish and other enemies. Just imagine a 

 soft clam (long-necked clam), in which the neck, or siphons and the 

 soft part of the body were from ten to twenty times as long as the 

 shell, and you will have an animal which closely resembles the pile- 

 worm. 



As it bores its way into the wood, the pileworm excavates for itself 

 a burrow, which opens to the outside through a small pore not larger 

 than a pinhole (fig. 3). Through this small opening it projects two 

 small tubes, or siphons, the lower (ventral) one being the longer, the 

 upper (dorsal) one much shorter. By means of millions of microscopic 

 hair-like structures, known as cilia, which are beating in one direction, 

 a current of water is drawn in through the lower, or incurrent, siphon, 

 and expelled through the upper, or excurrent, siphon. The water in 

 its course through the body passes through the gills, as it does in other 

 bivalve molluscs. Here it gives up oxygen to the blood, while all food 

 materials are filtered out and carried to the mouth. For like its rela- 

 tives, the clam and the oyster, the marine borer lives mainly upon the 

 very small microscopic animals and plants in the water. It is still an 

 open question whether the borers may derive some nutriment from 

 the wood which is shaved off in making the burrow, but it should be 

 emphasized that the marine boring molluscs enter the bottom of your 

 boat, or the piling of your wharf, not primarily because the wood is 

 food for them, as it is for the wood-boring insects on land, but because 

 the wood furnishes them with a safe retreat where the soft parts of 

 the body are protected. 2 



Pileworm Repels Invaders 



The common soft clam buries itself in the sand, leaving only a small 

 hole above it through which its siohons are pushed up to the water. In 

 much the same way the marine boring molluscs depend upon the very 

 small opening through which they entered the wood for keeping in 

 touch with the outside world. But just here the marine borer goes the 

 clam one better. Those of us who have dug soft clams have seen the 

 long red sand worms or clam worms, which crawl down the hole made 

 by the siphons of the clam, and devour the luckless bivalve at the bot- 

 tom. No such thing can happen to the pileworm, however, for like 

 many troublesome pests it has developed means of repelling invaders. 

 On either side of the siphons is a spade-like structure, made of lime, 

 which bears two sharp points on its outer ed^e (fig. 2) J These struc- 

 tures, known as pallets, are attached to muscles by which they may be 

 forced together into the hole at the end of the burrow (fig. 3) or 



2 Harington (2) finds that the larvae of Teredo norvegica are strongly at- 

 tracted to an alcoholic or an ethereal extract of sawdust, and also to a 1 per 

 cent solution of malic acid. He finds a slight hydrolysis of cellulose by 

 enzymes extracted from the digestive gland of Teredo, indicating that at least 

 during the period of growth and burrow enlargement the pileworm may derive 

 some nutriment from the wood. ,. - h ,,•.- . -, , T .^,.,,j , ; . 



