of magnitude dose level employed. Mean total hydrocarbon concentrations (± 
s.d.) measured during each experiment are given with the results; between 
treatment, mean hydrocarbon values were significantly different for all 
experiments (P < 0.05). 
All three gastropod species studied produce egg capsules. While C. fornicata 
broods its capsules, U. cinerea and N. obsoletus attach capsules to solid 
substrates and then abandon them, making these capsules easy to collect and 
count. Descriptions of larval development have been published for N. obsoletus 
(29), C. fornicata (34) and C. irroratus (28). 
Adult Mud-Snail Survivarship and Egg Capsule Deposition 
Experiments with adult mud-snails were conducted in the flow-through 
dosing system described above. Adults of N. obsoletus were collected from 
Bissell Cove, Rhode Island, and groups of 35-100 individuals placed in circular 
plastic containers (26 cm diameter, 6 cm high) and completely submerged in 
the dosing tanks. The top and sides were perforated to permit water 
circulation. Surface area of the top and side of each container was 
approximately equal. Snails were fed shredded Mercenaria mercenaria tissue 
weekly, and the number and position of deposited egg capsules were recorded 
before capsules were removed each week. All container surfaces were wiped 
clean after each examination. Dead snails were counted and removed 
periodically. The mean number of eggs per capsule was determined for N. 
obsoletus in all treatments. Since N. obosoletus is primarily a deposit feeder 
(30), and sediments are known to accumulate petroleum hydrocarbons from 
seawater (15, 17), one experiment was run with mud added to evaluate its 
influence on toxicity. 
Reproduction of Urosalpinx cinerea 
Specimens of U. cinera were collected at Jamestown, R.I., in May, 1976, 
and groups of ten individuals were placed in perforated plastic freezer 
containers. Three boxes were submerged in the flow-through system at each of 
the following nominal oil levels: control (0.0 ppm), 0.01 ppm, 0.1 ppm. 
Freshly collected barnacles were provided weekly as food. Once each week, 
deposited egg capsules were counted and then removed. In July, a sample of 
egg capsules was taken from each treatment level to determine the mean 
number of eggs encapsulated. The number of females present in each container 
was determined in the middle of the experiment using the live-sexing technique 
of Hargis (13). 
137 
