An analysis and a comparison of abundance, prevalence and distribution patterns for three temnocephalid species are presented. Three temnocephalid populations from Río de la Plata river, República Argentina, were studied: Temnocephala digitata Monticelli, 1902 associated with Palaemonetes argentinus Nobilli, 1901 (Crustacea Caridea), T. axenos Monticelli, 1899 associated with Aegla uruguayana Schmitt, 1942, and A. platensis Schmitt, 1942 (Crustacea Anomura) and T. iheringi Haswell, 1893 associated with Pomacea canaliculata (Lamarck, 1822) (Mollusca Gastropoda). These host species provide different environments and consequently different opportunities for the development of their symbionts. Increasing gradients of abundance and prevalence, and a decrease in the aggregation index (k) were observed. The distribution pattern of the three symbiotic species is aggregated. The original distributions were compared with the parameters of the negative binomial. The observed overdispersion may be due to heterogeneity of the host population and reproduction of the commensal within the host.