Unveiling cryptic aeglids: new species of the Aegla longirostri complex (Decapoda: Anomura) from southern Brazil

The genus Aegla Leach, 1821, currently comprising more than one hundred described species, represents a unique lineage within the infraorder Anomura MacLeay, 1838. The family Aeglidae Dana, 1852 is the only anomuran family of marine origin that is now entirely restricted to freshwater habitats. Aeglids are among the world’s most endangered crustaceans, with their conservation challenged by the existence of cryptic species. To date, eight aeglid species complexes have been identified, including the Aegla longirostri complex, which contains at least 14 putative species distributed across northern, central, and eastern Rio Grande do Sul state, Brazil. In this study, we describe and delimit the extent of occurrence of two sympatric species of the Aegla longirostri complex from the Alto Jacuí River Basin. We conducted regional sampling and used mitochondrial COI gene sequences for phylogenetic reconstruction and molecular species delimitation. The two new taxa, Aegla espraiada sp. nov. and Aegla jacuiensis sp. nov. , exhibit restricted distributions. Aegla espraiada sp. nov. was recorded at three localities, whereas Aegla jacuiensis sp. nov. is known from a single site. Among the characteristics that can differentiate them are the scales on the rostral carina, the shape of the anteromesial region of the third thoracic sternite, and the ventral angle of the second epimere. Given their limited ranges and ongoing agricultural expansion in the region, both species can be considered at risk of extinction.