Assessing the role of taxonomic impediment in the knowledge on geographic distribution of Physidae (Gastropoda: Hygrophila) in South America, using an intensive-data approach.

There is a marked disparity in the state of knowledge of Holartic x Neotropical species of the freshwater snail family Physidae; the incipiency of data on Neotropical physids reflecting the lower number of dedicated specialists. The gaps in the knowledge on Neotropical physids have led to historical uncertainty about species validity. Revisiting the species is essential to reduce taxonomic impediment and delineating their probable distribution is the first step to attain this purpose. We aimed at critically analyze occurrence records of South American physids, compiled through an intensive search in the literature, biodiversity and molecular databases. We present a provisional characterization of the distribution of this family in South America, considering the probable versus the poorly documented distribution of the species. The critical underrepresentation of South American physids in collections, molecular databases and literature reinforces the role of taxonomic impediment in delaying the advance of the knowledge on species diversity. Malacological collections represented the main source of records, evidencing the relevance of unpublished data associated to specimens to assess distributional information on neglected groups. As most of the species are represented by shells, the reassessment of species identity and distribution must be done, using molecular and anatomical criteria for species delimitation.

Diversity and Distribution of Peritrich Ciliates on the Snail Physa acuta Draparnaud, 1805 (Gastropoda: Physidae) in a Eutrophic Lotic System.

Bianca Sartini, Roberto Marchesini, Sthefane D ´ávila, Marta D'Agosto, and Roberto Júnio Pedroso Dias (2018) Freshwater gastropods represent good models for the investigation of epibiotic relationships because their shells act as hard substrates, offering a range of microhabitats that peritrich ciliates can occupy. In the present study we analyzed the community composition and structure of peritrich epibionts on the basibiont freshwater gastropod Physa acuta. We also investigated the spatial distribution of these ciliates on the shells of the basibionts, assuming the premise that the shell is a topologically complex substrate. Among the 140 analyzed snails, 60.7% were colonized by peritrichs. We observed seven peritrich species: Epistylis plicatilis and Epistylis sp. (Epistylididae); Opercularia articulata (Operculariidae); Carchesium polypinum, Vorticella campanula and Vorticella sp. (Vorticellidae) and Thuricola kellicottiana (Vaginicollidae). We observed a high prevalence of epibiosis (> 60%) when all species of ciliates were considered conjunctly. However, the prevalence was low (1-58%) when each species was considered separately, reflecting their aggregate distribution pattern. The most prevalent species were Epistylis sp. (58.60%), Vorticella sp. (14.30%) and O. articulata (13.60%). Although the epibionts were distributed through the shell's entire extension, we observed greater values of abundance, density, diversity and dominance on the dorsal surface. Only Epistylis sp. was widely distributed on the ventral surface. We also observed that the peritrichs predominantly occupied the areas of the shell delimited by the sutures. We interpreted these distribution patterns considering that the peritrichs select their attachment sites under pressures related to basibiont behavior, physical forces that may dislocate them and protective characteristics of the shell's areas.

Occurrence of Trichodina heterodentata (Ciliophora: Trichodinidae) infesting tadpoles of Rhinella pombali (Anura: Bufonidae) in the Neotropical area.

Data on trichodinid ciliophorans in Brazil are scarce and generally do not use the modern silver-impregnation technique, which is essential to the taxonomy of the group. The present study reports not only on the first occurrence of Trichodina heterodentata in Brazil but also on the first record of this trichodinid infesting tadpoles of the species Rhinella pombali. This study also constitutes a second report on T. heterodentata from tadpoles. In September 2007, tadpoles were collected from a stream in a small farm in the agricultural area of the city of Juiz de Fora, southeastern Brazil. The ciliophorans found on the tadpoles' bodies and tails were submitted to techniques such as silver impregnation and scanning electron microscopy. Our biometric data of T. heterodentata population infesting Rhinella pombali were compared to five other South-African populations of T. heterodentata infesting tadpoles of Xenopus laevis laevis. Results were discussed in terms of low host specificity as well as the wide geographical distribution of this trichodinid.