This study contributes to the understanding of the population dynamics of the clam Megapitaria squalida, a species for which information on growth and age structure remains limited. To describe its growth, 1,116 intertidal clams were collected between November 2012 and November 2013 from Navachiste Bay, a coastal lagoon located in the Gulf of California. Age was estimated by counting growth rings on the shell surface. Ring periodicity was validated through edge analysis, considering the annual alternation of opaque and hyaline bands. Individual growth was evaluated using a multimodel approach that included six versions of the Schnute growth model, parameterized assuming normal, log-normal, and logistic error distributions. Model selection was based on the Bayesian Information Criterion (BIC). The results indicated annual deposition of growth rings. The hyaline edge was observed from June to October, reaching a frequency of 100% in clams collected in October. Six age classes were identified, with age classes 1 and 2 being the most abundant. A sigmoidal growth curve corresponding to Schnute model version 1 provided the best fit to the data. Models parameterized with a logistic error distribution yielded the lowest BIC values compared with those assuming normal and log-normal error distributions, indicating better relative performance among the models evaluated. External rings were readily distinguishable and may provide a practical and cost-effective method for age estimation. This study represents the first validation of growth-ring periodicity through edge analysis in M. squalida and provides evidence of the potential usefulness of the logistic probability density function for parameterizing individual growth models.
