The population model described here is a stochastic, density-independent matrix model for integrating the effects of toxicants on survival and reproduction of the marine invertebrate, Americamysis bahia. The model was constructed using Microsoft Excel 2003. The focus of the model is on laboratory populations because neither biological variability of field populations nor variability associated with time-varying toxicant concentrations, as might be expected in field situations, are considered. The model employs several aspects of traditional population viability analysis (PVA), establishing a dose-response relationship between exposure concentrations and estimates of expected minimum population size. This documentation describes the model, and also provides the justification for various default parameters for use when the ideal toxicity data set may not be available.