ABSTRACT The isopods of the family Cymothoidae are ectoparasites crustaceans that infest a wide variety of saltwater fish. This paper documented the first occurrence of Nerocila acuminata (Schiödte & Meinert, 1881) parasitizing the shortnose guitarfish Zapteryx brevirostris (Müller & Henle, 1841) (Rhinobatiformes, Rhinobatidae) in the southern Atlantic Ocean. This report can be an available tool to create a parasitology database for a species of conservation interest. It will also provide scientific data that can help the understanding of the biological factors acting in healthy populations and thus support the efforts made to preserve and conserve the species.

ABSTRACT Embryonic malformations can be a result of exposure toxic substances (pollution), lack of nutrients, physical restraint, genetic disorders, or infections and diseases. Such malformations can be classified according to severity and offspring survival outside the uterus. Moreover, abnormalities are normally restricted to a small portion of the litter, mostly, to only one embryo. Here, we report a case of congenital malformation dominance in an offspring of the shortnose guitarfish and compare it with other abnormalities commonly reported in batoids in addition to discussing the possible causes involved in the observed deformities.