Integrated morphological and ecological traits to identify Temnocephala digitata Monticelli, 1902 (Platyhelminthes, Temnocephalida) and neotype designation

Abstract

Within the Platyhelminthes, Temnocephalida is a clade of continental turbellarians that establish an ectocommensal relationship with their hosts. Many species live associated with decapod crustaceans. In the Neotropical region, two species of Temnocephala are commensals on species of the shrimp family Palaemonidae. Temnocephala digitata lives on Palaemon argentinus and was originally reported from freshwater bodies connected to the Río de la Plata, in Buenos Aires Province, Argentina. The original brief description of the species caused the name to be used incorrectly, creating confusion about the actual specific identity. Here we redescribe T. digitata based on morphological, biological and ecological features. Main morphological features of the reproductive system are the length of the cirrus and its introvert, as well as the number and disposition of its spines. Also, the female portion of the reproductive system lacks vaginal sphincters, which are otherwise well developed in the other species of the genus. The species is big and has the smallest adhesive disk reported for the genus, which allows firm attachment and active movements on the host surface. The egg capsules are fixed on the border of the gill chamber of the host. The prevalence, intensity, and abundance of T. digitata vary according to the size and sex of the host and throughout the year, with the highest prevalence, intensity, and abundance on ovigerous female hosts. This fact is related to the longer intermolt period of ovigerous hosts. These observations conform a solid redescription for a species with a tortuous nomenclatural history.