The amphipod HyalellaSmith, 1874 is exclusive to the Americas, and the South region of Brazil presents the greatest diversity of the genus. This paper presents two species of Hyalella from Santa Catarina state, Brazil. A new species from the municipality of Palmeira is characterized by oval eyes, absence of flanges, epimeral plates not accuminated, presence of three lateral pappose setae on article 4 in antenna 2, absence of plumose setae in the maxilliped, presence of comb-scales and absence of serrate setae in the gnathopods, presence of curved seta on the inner ramus of the uropod 1 and absence of lateral setae on the telson. A new species from Rio das Antas municipality main characteristics are absence of flanges, epimeral plates accuminated, absence of plumose setae and distal nail in the maxilliped, presence of comb-scales and absence of serrate setae in gnathopods, presence of curved seta on the inner ramus of the uropod 1 and absence of lateral setae on the telson. Here we expand the distribution and increase the morphological and taxonomic knowledge of the genus.

The genus Hyalella Smith, 1874 occurs exclusively in the Americas. In Brazil, the states of Santa Catarina and Rio Grande do Sul have the largest number of records with 20 species. This paper presents two new species for the state of Santa Catarina, Brazil. The serrate setae with accessory seta, a new type of seta, is registered for the genus and observed on gnathopods 1 and 2. Additionally, microtrichs are reported on articles, a detail that has not been mentioned in previous studies. Hyalella carsone sp. nov. is characterized by gnathopod 1 with comb-scales from the basis to the carpus, gnathopod 2 dactylus with proximal margin strongly serrated and the presence of serrate setae on the articles of gnathopods 1 and 2. Hyalella wangarie sp. nov. is characterized by gnathopod 2 palm not sinuous with margin inconspicuously serrated, peduncle and inner ramus of the pleopod with simple setae, presence of curved seta on uropod 1 of male and gnathopod 1 palm on female slightly serrated. In this work we expand the number of species from Brazil and increase the morphological knowledge of the genus Hyalella.

Accurate knowledge of the global distribution of non-indigenous species (NIS) is essential for understanding their invasion dynamics and for implementing timely management measures. This study reports the first records of the marine amphipod Aoroides longimerus, putatively native to the East Asian coast, in Italy (2018), Spain (2019) and Tunisia (2022) and provides the earliest documented record of the species in its introduced European range (Portugal, 2011). Furthermore, it expands the species’ known distribution in mainland Portugal (including the northernmost record), Macaronesia (with first records in the Canary Islands and Madeira), and confirms its presence along the Atlantic coasts of France and the Netherlands. Aquaculture facilities, particularly those associated with oyster farming, are probably the primary vector of introduction, while recreational boating may have contributed significantly to secondary dispersal. In comparison to other exotic amphipods, A. longimerus remains absent from many marinas, ports and/or aquaculture facilities in the Mediterranean Sea and adjacent regions, such as the Red Sea. This suggests that the species may still be in the early stages of expansion, or that its dispersal ability across marinas and ports is more limited than that of other amphipods. The present study, however, highlights several key ecological traits of A. longimerus: (i) it can survive year-round despite seasonal fluctuations, and reach high local densities, (ii) it exhibits strong colonisation capacity, as shown by its rapid establishment on settlement plates, and (iii) it displays opportunistic feeding behaviour, primarily consuming detritus. These characteristics underscore the importance of continuous surveillance and effective communication with stakeholders to prevent further expansion of this species.

The genus Bathyporeiapus Schellenberg, 1931, includes three intertidal amphipod species present in the southern region of South America: Bathyporeiapus bisetosus Escofet, 1970, and B. ruffoi Escofet, 1971, in the Atlantic waters and B. magellanicus Schellenberg, 1931, in the Pacific. Bathyporeiapus taxonomy is understudied, with records mainly from general intertidal fauna inventories. In this context, the present study provides a redescription of B. magellanicus and B. ruffoi , with comments on morphology of B. bisetosus . The type material of B. magellanicus , B. bisetosus , and B. ruffoi was analyzed, and new specimens of B. bisetosus and B. ruffoi were collected in the intertidal zone of the São Paulo and Rio Grande do Sul state, southern Brazil. Species differ in the number of T-setae on peduncle article 3 of antenna 2: B. magellanicus (3), B. bisetosus (2), and B. ruffoi (4), and in the number of articles on pereopod 7 dactylus: B. bisetosus (5–8), B. magellanicus (8–10), and B. ruffoi (14); also, B. magellanicus presents maxilla 1 with setae on the inner plate. Furthermore, the males of Bathyporeiapus species are not known, and in the present study, more than a thousand female and juvenile individuals were collected, but not males, reinforcing the need for studies on life history. An identification key for the three known species of Bathyporeiapus is given.

Hyalella Smith, 1874, is a diverse and ecologically important genus of freshwater amphipods widely distributed throughout the Americas, occurring from temperate North America to southern South America. Here, we provide a comprehensive overview of the current state of knowledge of Hyalella, integrating historical developments in its study with advances in taxonomy, systematics, biogeography, ecology, reproductive and population biology, and molecular research. Despite substantial progress in recent decades and an accelerating rate of species descriptions, several regions of the Americas remain poorly sampled, while cryptic diversity, unresolved species complexes, and limited molecular information continue to challenge estimates of the actual diversity and evolutionary history of the genus. Future research should prioritize integrative taxonomy combining morphological and molecular evidence, expanded geographic and habitat-based sampling, phylogenomic approaches, standardized genetic reference libraries, ecological and physiological studies, and the application of emerging tools such as environmental DNA and species distribution modelling. By integrating more than a century of research, this review identifies major advances and persistent knowledge gaps and provides a framework for future studies aimed at understanding the diversity, evolution, ecology, and conservation of one of the most distinctive freshwater amphipod radiations in the Americas.