This study focuses on aquatic mites from the Portuguese Exclusive Economic Zone, including the mainland area, and Madeira and Azores archipelagos, aiming at compiling all existing information and generating a list of species and all their data on collecting sites. For the present work, we consider aquatic species, those that inhabit the marine, deep sea, intertidal, freshwater, transition water or brackish environments, with life-cycle occurring entirely at water habitats or their vicinity. Furthermore, breeding should take place in water aquatic lifestyles. The dataset search for this checklist started with the first descriptions of water acarids from the Azores Archipelago performed by Théodore Barrois. Primary sources for occurrence confirmation were Süßwasserfauna von Mitteleuropa book collection, The Global Biodiversity Information Facility (GBIF), complemented with an extensive Portuguese literature review and data biodiversity websites, e.g., European Water Mite Research (Watermite.org). In total, 102 valid species were found belonging to 41 genera, and 19 families, nested in the orders Mesostigmata, Sarcoptiformes and Trombidiformes. This is the first work compiling all the species of aquatic mites found in Portuguese territory, as well as data of collection, serving as the basis for future studies.

The macrophyte Egeria densa Planchon, 1849 is a freshwater plant native to the subtropical regions of South America. Fast vegetative reproduction and efficient dispersal allow this species to form extensive beds that produce high levels of oxygen in freshwater ecosystems, generating microhabitats that act as refuge and nursery for an array of organisms, increasing sedimentation and light availability. Despite its undisputable ecological role, it is considered invasive and is present on all continents except Antarctica with the first records in Europe occurring at the 20th century. At the international Minho River (NW Iberian Peninsula), the observation of its presence was noted in the 1990s and is now an established population in this ecosystem. This study is the first descriptive-taxonomical assessment of the associated fauna with the exotic macrophyte E. densa, using both morphological and molecular approaches, three decades after its establishment in the international Minho River. Results indicate the presence of a faunal assemblage, composed a total of 20 identified species, including platyhelminths, hydrozoans, bryozoans, molluscs (Gastropoda), annelids (Oligochaeta and Hirudinea), crustaceans (Ostracoda, Copepoda, Branchiopoda and Amphipoda), aquatic mites and insects. Paludicella aff. articulata (Ehrenberg, 1831), Girardia sinensis Chen & Wang, 2015, Lebertia insignis Neuman, 1880 and Ceriodaphnia rigaudi Richard 1894 are recorded for the first time in Portugal.