The literature reported ectocommensals associated to Parastacus pugnax (Poeppig, 1835), but there are not ecological studies about abundance of these onP. pugnax. The aim of the present study was to analyze the abundances of ectocommensal Temnocephala chilensis (Moquin-Tandom, 1846), on P.pugnax. It had not correlation between T chilensis number with total length and total weight of F. pugnax. T chilensis has an associated spatial distribution and negative binomial distribution. Ecological and evolutive topics were discussed.