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 A', 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 Survivorship and Egg Capsule Deposition 



Experiments with adult mud snails were conducted in the flow-through 

 dosing system described above. Adults of A^. 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 sliredded 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 vdth mud added to evaluate its 

 influence on toxicity. 



Reproduction of Urosaipinx 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-througli 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 



