damage to oyster stocks (Cahn, 1950; 

 McKernan, Tartar, and Tollefson, 

 1949), little has been done to establish 

 the drill's order of preference for the 

 organisms it is known to attack. Chap- 

 man and Banner (1949) reported that 

 Ocinebra attacks Olympia oysters in 

 preference to bay mussels (Mytilus 

 edulis) and barnacles. A preliminary 

 study of Chew and Eisler (1958) indi- 

 cated that the Japanese drill preferred 

 bay mussels and Manila clams 



(Venerupis japonica) to Pacific or 



Olympia oysters. In addition, this study 

 suggested that these drills miight de- 

 velop a preference for a particular 

 species of food. 



The present study was made between 

 July 4 and November Zl, 1957, in the 

 salt-water aquarium of the College of 

 Fisheries, University of Washington. 

 The purpose of the experiment was 

 two-fold: 



1. To ascertain if Ocinebra japonica 

 exhibited discrimination in its choice 

 of food when given an equal opportunity 

 of attacking any of four species of 

 bivalves (bay mussel, Manila clam, 

 Olympia oyster, and Pacific oyster). 



2, To determine if a relationship 

 existed between the thickness of shell 

 of the food organism and the time 

 required for Ocinebra japonica to per- 

 forate the shell and finish feeding. 



EQUIPMENT AND MATERIALS 

 Aquaria 



Four cement aquaria were used in 

 this study. Inside dimensions of each 

 aquarium measured 61 cm. wide, 140 

 cm. long, and 66 cm. high. The smooth 

 bottoms and sides of the four aquaria 

 were painted dull black. The two longer 

 sides of each aquarium were of plate 

 glass, covered with dark paper to pre- 

 vent light from entering through the 

 sides. 



Water 



Water level in the four aquaria was 

 maintained at 30 cm. Sea water from 



Puget Sound was recirculated through 

 the aquaria at the rate of 1 liter per 

 ZO seconds. Inflow and outflow of water 

 were at opposite ends of the aquaria, 

 approximately 13Z cm. apart. 



Water was directed into each aquar- 

 ium striking against the wall. A piece 

 of wood lath was placed across the 

 inflow side of the aquarium to prevent 

 foam from floating across the surface. 

 Water then flowed out through a tilted 

 drain pipe. 



Throughout the study, water tem- 

 perature was maintained at 11.9° C. 

 (+0.30° C.) by refrigeration units of the 

 salt-water system. It is unknown 

 whether this was or was not the opti- 

 mum temperature for active drilling 

 and feeding of Ocinebra japonica, since 

 virtually nothing is known about the 

 feeding of this species of drill in re- 

 lation to temperature. It is generally 

 understood that the water temperature 

 is an important factor governing the 

 feeding rate of Urosalpiux cinerea 

 (Carriker, 1955; Cole, 1942; Hancock, 

 1959). In the United States, the tem- 

 perature at which Urosalpinx com- 

 mences drilling varies in different 

 localities (Carriker, 1955), from 

 6.5 C. in Virginia (Carriker, 1955, 

 cited by Hancock, 1959) and 7.5° C. in 

 Long Island Sound (Hanks, 1957) to 

 15.0° C. in North Carolina and Virginia 

 (Federighi, 1931). Cole (1942) found that 

 Urosalpinx in England commenced 

 drilling as soon as the water tempera- 

 ture exceeded 11.0-12.0 C. Hancock 

 (1959) found that Urosalpinx kept in the 

 Fisheries Laboratory at Burnham-on- 

 Crouch, Essex, in 1953 continued feed- 

 ing until the average water temperature 

 dropped to 9.0-10.0° C. 



When test animals were collected in 

 the field water samples were taken to 

 measure changes in hydrogen-ion con- 

 centration (pH) and salinities to which 

 the drills were subjected in being 

 transferred from the field to the aquar- 

 ium. Results of the sampling are as 

 follow s : 



Exp. I, 6/27/57 in field, pH 7.85 and 

 salinity 28.12 %o 

 6/28/57 in aquarium, pH 7.15 

 and salinity 29.40 %o 



