Ergasilid copepods represent one of the commonest groups of fish parasites in Brazil. Within Ergasilidae, three genera share a peculiar latching mechanism on the antenna that completely encircles the gill filament, one of which is Acusicola Cressey, 1970. During a survey of estuarine fish from the Brazilian Amazon Coast, a new species of Acusicola was found on the gills of the largescale foureyes Anableps anableps (Linnaeus, 1758) (Actinopterygii: Anablepidae) in São Marcos Bay, State of Maranhão. Acusicola rochai n. sp. can be distinguished from its closest congeners mainly by three protrusions on the dorsal surface of third and fourth pedigerous somites, and by smooth interpodal plates. This work is the first report of a parasitic copepod infesting a fish from Anablepidae and, consequently, the host An. anableps. The existing dichotomous key proposed for the genus Acusicola includes only ten species, excluding the eight species subsequently described. Therefore, in the present work, a new dichotomous key is provided based on reliable and well-documented features.
The morphology of female bopyrids is adapted to parasitism, but understanding the function of their thoracic and mouth appendages is hindered by their small size and cryptic lifestyle, limiting detailed examination. This study aimed to clarify the function of the first oostegites and maxillipeds in bopyrid isopods infesting the branchial chamber of caridean shrimp through behavioural observations and morphological examination. We tested whether the movement of these structures was exclusive to ovigerous female parasites during brood ventilation. The results revealed that the beating of the maxillipeds and flapping of the first oostegites were not restricted to ovigerous females. However, the frequency of these movements was significantly higher in ovigerous females than in non-ovigerous females. The frequency of maxilliped beating increased with embryonic development, whereas that of flapping the first oostegites exhibited the opposite trend. Microscopic observation using dye showed that the movements of the maxillipeds and the first oostegites expelled residual dye from the female brood chamber through the dorsal surface or beneath the first oostegites. The dye was then transported by the water current generated by the scaphognathite of the host shrimp. These findings suggest that these structures not only facilitate ventilation but also serve as a grooming mechanism for female parasites, which is critical for embryonic survival. The results of the present study represent the first observation of embryo grooming in bopyrid isopods. This study also provides new information on the functional morphology of bopyrid isopods, which is important for understanding their ecological dynamics and adaptation to parasitism.