MOLLUSCA 



151 



great damage to the piles in Pacific and Eastern harbors/ At- 

 tempts by the United States Navy to protect wharves and piles 



IS 



Fig. 67. Teredo navalis. Age five weeks from metamorphosis. 6", shell ;F, foot; /j, 

 incurrent siphon; es, excurrent siphon;/), pallet. (B. H. Grave, Biol. Bull., Oct. 1928.) 



A 



have resulted in the sheathing of some docks with concrete 



pregnation of the piles with creosote has also 



given a large measure of protection (Figure 



67). The borer {Pholas) is able to penetrate 



rocks and cement. It has extremely long 



united siphons and a shell with a file-Hke 



surface. 



Class 2. Amphineura. (Figure 68.) — The 

 chitons are bilaterally symmetrical molluscs 

 with eight calcareous plates or shields which 

 protect the dorsal surface of their boat-shaped 

 body. Like the wood louse and armadillo 

 they are able to roll themselves into a ball for 

 protection. In some species the shell plates 

 have between eleven thousand and twelve 

 thousand primitive visual organs. Chitons 



Im- 



Fig. 6 8. Chiton. 

 (From Hertwig-Kingsley, 

 Manual of Zoology. 

 Courtesy of Henry Holt 

 &Co.) 



^ Grave, B. H. 1928. Natural history of shipworm. Teredo navalis, at Woods 

 Hole, Mass. Biol. Bull., vol. 55, no. 4, pp. 260-282. 



Hill, C. L., and Kofoid, C. A. Marine Borers and Their Relation to Marine 

 Construction on the Pacific Coast. Final Report of the San Francisco Bay Marine 

 Piling Committee. 1924. 



Sigerfoos, C. P. 1908. Natural History, Organization and Late Development 

 of the Teridinidae or Shipworms. Bull. U, S. Bur. Fish., vol. 27, p. 191. 



