2. Test animals collected in the field 

 were measured for length. After 

 the measurement, a size range for 

 each species was selected around 

 the mean to represent the sizes of 

 drills and bivalves most abundant 

 in the area of collection. 



3. Two experiments, each of 70 days 

 duration, were conducted in which 

 individually marked Oc ine bra 

 japonica were presented with a 

 choice of four different food or- 

 ganisms: bay mnssels. My tilus 

 edulis; Manila clams, Venerupis 

 japonica; Pacific oysters, Crasso- 

 strea gigas; and Olympia oysters, 



Ostrea lurida. 



4. Drills generally preferred Manila 

 clams, Olympia oysters, or bay 

 mussels to Pacific oysters. 



5. Tanks, which differed in the num- 

 ber of various species drilled 

 and eaten, were also found dif- 

 ferent in the distribution of first 

 attacks. 



6. Results showed that a drill usually 

 continues to attack the same spe- 

 cies of food organism that it had 

 attacked previously and does not 

 tend to move to another organism 

 of a different species. 



7. The duration of drill attacks on 

 an individual species of food ani- 

 nnal was the same for the tanks 

 that were compared. The duration 

 of drill attacks between species 

 were significantly different. 



8. The results indicated that, on the 

 average, the drills took 7 to 8 

 days to drill and finish feeding 

 on Manila clams, 6 to 7 days for 

 Olympia oysters, 5 to 6 days for 

 Pacific oysters, and 4 to 5 days 

 for bay mussels. 



9. Variations in duration of attacks 

 were probably the result of the 

 differences in thickness of bivalve 

 shells rather than in the time 

 required to consume the edible 

 parts. 



10. An Ocinebra frequently drilled 

 halfway through a prey's shell, and 

 then moved to another prey. 

 Another drill sometimes moved 

 onto the first prey and usually 

 continued drilling in the same hole. 



11. It was not unconamon to observe 

 two or three Japanese drills at- 

 tacking a single bivalve. 



LITERATURE CITED 



CAHN, A. R. 



1950. Oyster culture in Japan. U.S. 

 Fish and Wildlife Service, Fish- 

 ery Leaflet No. 383, 80 pp. 



CARRIKER, M. R. 



1954. A review of those aspects of 

 the biology of the oyster drill 

 Urosalpinx Cinerea (Say) funda- 

 mental to its control. 1953 Con- 

 vention Papers, National Shell- 

 fisheries Association, pp. 51-66. 



1955. Critical review of biology and 

 control of oyster drills Urosal- 

 pinx and Eupleura. U. S. Fish 

 and Wildlife Service, Special 

 Scientific Report- -Fisheries No. 

 148, 150 pp. 



CHAPMAN, C. R. 



1956. Feeding habits of the southern 



oyster drill, T^ais haemastoma. 



1955 Proceedings, National 

 Shellfisheries Association, vol. 

 46, pp. 169-176. 



CHAPMAN W. M., and A. H. BANNER. 

 1949. Contributions to the life his- 

 tory of the Japanese oyster drill, 

 Tritonalia japonica with notes on 

 other enemies of the Olympia 

 oyster, Ostrea lurida. Washing- 

 ton State Department of Fish- 

 eries, BiologicalReportNo. 49A, 

 pp. 170-200. 



CHEW, K. K. and R. EISLER. 



1958. A preliminary study of the 

 feeding habits of the Japanese 

 oyster drill, Ocinebra japonica. 

 Journal Fisheries Research 

 Board of Canada, vol. 15, No. 

 4, pp. 529-535. 



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