MOLLUSCS. 



285 



! 



U 



lil.'4 

 I 



^ i 

 i 



i 



V * 



M 



I'. A 



an accident sank a coasting boat near St. Sebastian in Spain. Four montlis later some 

 iishermen raised the vessel, hoping to turn the materials to advantage, if not to repair 

 the vessel itself, but in the short space of time that had 

 elapsed, the planks and timbers vi^ere so completely riddled 

 by the Teredos that they were valueless. Tliere is a curious 

 fact noticed in connection with their burrowing. No 

 matter how many of these molluscs gain entrance to the 

 'same piece of wood, their tubes never interfere with one 

 another, but there is always left at least a thin partition 

 between two adjacent burrows. 



Since their appearance in Holland so long ago, these ship-worms 

 have done an incredible amount of damage to wharves, shijss, etc., 

 and many devices have been suggested for checking their ravages. 

 The use of chemicals, creosote, etc., has but comparatively slight 

 effect, for since these animals do not eat the wood, the chemicals do 

 not poison them. While kyanising (soaking the wood with creosote) 

 is an effectual check against that injurious crustacean, the gribble 

 (Ziimnoria liffnorum), it is but a slight defence against the Teredo. 

 In N^orway, timbers which were saturated with creosote under a 

 pressure of ten pounds to the square foot were found two years 

 later to be filled with the molluscs. To iron rust they have a de- 

 cided aversion, and piles and other timbers which are driven full of 

 broad-headed nails escape their ravages. Our modern vessels also 



escape their injurious action, thanks to 

 the copper sheathing with which their 

 hulls are covered. On our coasts south 

 of Cape Cod, it is customary to coat all 

 spars and buoys with verdigris paint, 

 and to take them up every six months 

 for cleaning and a new coat of this 

 poisonous paint. Notwithstanding this, 

 the average life of a buoy is only about 

 twelve years, but half of which is spent 

 in the water. 



On our coast, Teredo navalis is the 

 most common and most injurious spe- 

 cies, but three other species of Teredo 

 and one of JCylotrya, an allied genus, 

 occur in larger or smaller numbers. ' In 

 tropical waters many other forms occur, 

 of which we need only mention T. 

 corniformis, which burrows in the 

 husks of cocoa-nuts and other woody 

 fruits floating on the sea, and the gigantic Septaria 

 arenaria, of the Philijiipine Islands, which burrows in 

 the sand, sometimes attaining a diameter of two inches 

 and a length of nearly six feet. 



Pholas and its allies are also burrowing forms, but, unlike those just mentioned. 







Fig. 313.— Teredo/Or 

 taliSy ship-worm. 



Fig. 314. — Teredo navalis. 



