ABSTRACT. – The first record of the invasive clam Mya arenaria in the Iberian Peninsula was reported by Guimarães & Galhano in the “Mya zone”, Lima estuary. However, we hypothesize that these authors taxonomically confused Mya arenaria with the native clam Scrobicularia plana. Our results point in this direction from a species and a bionomical approach. Population parameters such as density or asymptotic shell length and the analysis of the expected composition of the macrobenthic assemblages support our findings. Nonetheless, Mya arenaria is actually present in the Lima estuary: apart from empty shells of the invasive clam lying on the sediment surface, at least a low density population was observed in a lower intertidal level off the “Mya zone”. Shell length comparisons strongly suggest that the invasion happened earlier in northern Portugal than in the Tagus estuary, where the invasive clam was recently reported to be established.