The introduction of non-native species is a constant concern around the world since it represents one of the main threats to biodiversity, impacting negatively on native populations, some of them with commercial importance. Hence, monitoring these introductions is fundamental to the management and conservation of the biodiversity of a region. Herein, we report the presence of Moerisia cf. inkermanica in the ballast water of oil tankers loaded at the Cayo Arcas oil terminal. The taxonomy of Moerisia members is uncertain due to the lack of comprehensive morphological descriptions and the few molecular data available. So, we provide a detailed morphological comparison among its congeners. The taxonomic identity of the specimens was determined based on the length of the perradial lobes of the manubrium, the number of tentacles, and the features of their nematocyst rings. Some Moerisids are considered invasive in different localities of the world. However, this genus had not been reported in coastal ecosystems of the Gulf of Mexico over the years until now. Sampled tankers came from different ports of the region, mainly from the northern Gulf of Mexico. Therefore, we encourage systematic monitoring of these ecosystems to recognize the establishment of this species as invasive in the region, know its population dynamics over time, and evaluate the possible ecological impacts that could exert on native populations.