462 



MARINE INVERTEBRATES 



curious; it may be observed also in several deep-sea genera and in cer- 

 tain extinct fossil forms. The length of this shell is about two inches. 

 This species also occurs in California, 

 where its favorite station is in hard tena- 

 cious clay. Length two to four inches. 



FAMILY TEREDINIDJE 



GENUS Teredo 



T. navalis. 



Zirphcea crispata. 



Teredo navalis, in a piece of tim 

 ber: P, pallets; S.S, siphons 

 T, tube ; V, valve of shell. 



This species is worm- 

 like in form, but 

 it has a small bi- 

 valve shell at the 

 larger end, and 

 near the anterior 

 extremity two 

 calcareous ap- 

 pendages called 

 pallets, beyond 

 which extend two 

 siphons. Along 

 the surface of the 

 mantle is secret- 

 ed a continuous 

 shelly tube which 



lines the burrow. This mollusk, commonly called 

 the " ship- worm," is exceedingly destructive, per- 

 forating with its burrows submerged timber 

 and soon rendering it useless. Various means 

 are taken to protect ships, the piles of wharves, 

 buoys, and the like, against its ravages j copper 

 sheathing, large-headed nails driven close to- 

 gether into the wood, verdigris paint, and so 

 on, being used with more or less effect. Vast 

 numbers of these animals enter the wood and 

 burrow in various directions, but they never 

 interfere with one another, a thin partition of 

 wood always being left between adjacent bur- 

 rows. How they effect the burrowing is not 

 determined, but it is supposed to be by means 

 of the pallets. Teredo does not, like the boring 

 isopod Limnoria lignarum, feed upon the wood. 

 Its food consists of microscopic organisms which 

 are taken in through the incurrent siphon. In 

 temperate waters T. navalis grows sometimes to 

 the length of six inches ; in tropical waters it 

 attains the length of two feet. 



There are three other species of Teredo and one 

 of the genus Xylotrya on our Northern shores ; 

 T. navalis is, however, the most common and 

 most destructive. In Southern waters there are 

 many other forms of these boring mollusks. 



