8 . Soft muddy bottoms and to a lesser degree sandy bottoms, devoid of 

 haid objects; aie probably unfavorable for the growth, multiplication, and loco- 

 motion of the drill. 



9 At summer temperatures drill mortality rates increase rapidly as 

 salinities falL but this rate is markedly reduced as temperatures drop, so that 

 at low winter temperatures drills can withstand unusually low salinities for pro- 

 tracted periods. Minimum survival salinities at summer temperatures appear 

 to vary from 12 to 17 o/oo in different regions 



10. Activities of Urosalpinx are noticeably influenced by temperature, and 

 the initiation and cessation of these activities varies in different geographic regions 

 Locomotory movement takes place it different regions in a thermal range approx- 

 imately 2 to 10°C; feeding and drilling, 7 to 15°C; and oviposition 11 to 20°C, 



11. At current velocities above 1.25 cm. /sec, Urosalpinx turns into and 

 moves against the current; at velocities below this no rheotaxis is displayed. A 

 pronounced negative geotaxis is exhibited at temperatures approximately above 

 10"C, In strong light drills move away from the source of light; in dim light, 

 toward it; and at weaker intensities the phototactic response is lost completely. 

 Chemical attraction plays an important role in food selection by the drill. 



12. A number of physiological races and at least two morphological sub 

 species of Urosalpinx cinerea o ccur . 



13 . The oyster drill is preyed upon by its own kind, by Polinces , 

 Astenas, and possibly other animals, but the degree of predation is probably 

 slight It is host to at least three parasites . 



14. The bulk of the drill population probably migrates only to a limited 

 degree, particularly over oyster bottoms; occasional exceptions may be explained 

 on the basis of phoresis. The majority of drills or. firm bottom devoid of oysters 

 tend to move at an average rate of 15 to 24 feet per day in the direction of food. 

 An unknown proportion of drills in populations near shores migrate lntertidally 



to spawn. The "sudden appearance" of high concentrations of drills on oyster 

 bottoms may be explained on the basis of incomplete removal of young drills and 

 the subsequent growth of these, rather than on the basis of mass migration alore. 



15. Eupleura caudata, close relative of U cinerea, generally constitutes 

 only a small percentage of the drill population within the range of these two species, 

 but may be increasing In certain favorable areas . It is more active in oviposition 

 than Urosalpirx, ovipositing an average of about 22 eggs per case . 



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