Spond^/'lus pictorum was the aost conspicuoios molluslc in the shallov; v;ater. The 

 shells of this lanellihraiich are so fimly cemented to rocks that it in verj^ difficult to 

 ohtain hoth valves of an adult specimen. The majority of shells brou^^ht hj'- the diver v;ere 

 ahout 20 021. long, one valve v/eighing as nuch as U pounds (l.S kilos). The thiclcness of 

 shell varied from 3 to 5*5 era. The shells of yovxig Spondylus pictorimi have long c-'jj.'ved 

 spines. In old specimens, they are usually lostj "but in the speciciens measuring ahout 

 12 en. , some of the Spines are still noticeable. It is difficult to understand why 

 Spbnd.;.^lus secretes such a heavy shell. In Pansxia, this nollusk lives attached to rocks 

 heyond low v;-ater, v/here it is not affected hy the pounding of the surf. The outside surface 

 of the shell is heavily overgrovm by nanj,^ fouling organisms, among v/hich the most conspic- 

 uous are the shells of Chama huddiana C. B. Adams, and the calcareous tubes of annelids. 

 Many small hydroids, sea anemones, sponges, and other invertebrates are attached to the 

 shell. The valves axe heavily infested by a boring sponge, Cl iona sp. , which penetrates to 

 about 1/3 of the thickness of the shell, and by a boring mollusk Lithophaga aristata 

 Dillwyn. The high intensity of infestation by this species becomes apparent only after the 

 removal of the outside lajrer of shell (Fig. 19). One specimen, with surface ai-ea of shell 

 of 75 square Inches, was infested by 383 Lithophagae; or, on the average, each sauare inch 

 of shell surface contained 5 holes made by this borer. The majority of holes v/ere small, 

 about 2-3 mm. in diameter, but there v;ere 23 large oblong cavities about h cm. long v;hich 

 penetrated almost the entire thickness of the shell. Only a thin layer of apparently 

 rapidly laid mother-of-pearl separated these cavities from the soft parts of the mollusk. 

 It apxieaxs that rapid deposition of shell substance is the only meajis at the disposal of 

 Spondylus in protecting itself against the borers. Thus, the ability to produce verj"- thick 

 shell and to continue the deposition of shell substance as the latter is penetrated by 

 borers is probably a method of defense which has great survival value to the species. 



Among other lamellibranchs, mention should be made of the rock oyster, Ostrea 

 megodon Hanley, v/hich is generally distributed and is used for food. The oyster averaged 

 15-16 cm. in length. Its meat is rather tougli but palatable. 



/^ ♦. 











I--. 



Figure I9 Spond^^lus pictorum v;ith outer layer of shell removed to show 



infestation bj'' boring sponge (small holes), and boring Eiollusk, 

 Lithophaga aristata (large holes). 



30 



