Monhystera denticulata Timm, a free-living nematode present in the aufwuchs assemblages of several marine macrophytes located in North Sea Harbor, Southampton, New York, was isolated from Zostera marina and established in laboratory culture in order to study the influences of temperature and salinity on its life history. Under experimental conditions, M. denticulata has a generation time (Measured as the time elapsing between the first egg depositions of consecutive generations) of 10-12 days at 25Β° C and 26β° S, which represent optimal growth conditions in the laboratory. The organism has a generation time of 20 days at 25Β° C and 13β°, 17 days at 25Β° C and 39β°, 18 days at 15Β° C and 26β°, 36 days at 15Β° C and 13β° and 34 days at 15Β° C and 39β°. As conditions vary from the optimum of 25Β° C and 26β° S, a decrease in temperature of 10Β° C and an increase or decrease in salinity of 13β° results in a doubling of the generation time. At 5Β° C the generation time is about 180-197 days.Assuming optimum conditions and average generation time, about 15 generations of M. denticulata could occur in North Sea Harbor during the year. The number of generations occurring in reality is probably less, however, due to the fact that the females deposit their eggs over a period of several days.