Clinostomum cf. complanatum (Rudolphi, 1819)

Hosts (prevalence; range): L. podicipinus (2/225; 1–6).

Site of infection: body cavity.

Stage: encysted larva.

Type host and type locality: Ardeae cinerea Linnaeus (bird), Berlin, Europe.

Comments: Clinostomum complanatum was described as Distoma complanatum by Rudolphi, but there are questions concerning the precise year of publication which could be from 1809 to 1899 (Dowset & Lubinsky 1980). Leidy (1856) established the genus Clinostomum for adult worms found in birds from USA and C. complanatum is the type species (Kanev et al. 2002). Several debates concerning species of Clinostomum remain among researchers, especially regarding the metacercariae of C. complanatum and Clinostomum marginatum Rudolphi. These two species have already been considered as synonymous due to their morphologic similarity (e.g. Baer 1933; Yamaguti

1933; McAllister 1990). Dzikowski et al. (2004) separated these species based on differences in ribosomal DNA, but the authors use specimens from Israel instead of those from North America. Caffara et al. (2011) integrated morphological and molecular tools such as ITS and COI sequences from specimens from North America and Europe, and they concluded that C. complanatum and C. marginatum are distinct. Both species are widely distributed and have a similar life cycle involving a bird as the definitive host and a fish or an amphibian as the second intermediate host (Dias et al. 2003; Caffara et al. 2014). Five species of Clinostomum (C. complanatum, C. marginatum, Clinostomum attenuatum Cort, Clinostomum hylaranae Fischthal & Thomas, and Clinostomum pseudoheterostomum Tubangui) have been reported as metacercaria in salamanders, toads, and frogs mainly from North America; only one record in Asia, Europa, and Africa (Calhoun et al. 2020). We observed the following features of C. complanatum in our metacercariae: genital complex in the posterior end of the body, testes in tandem with an irregular shape, ovary displaced to lateral and smaller than ootype, cirrus sac with the same size or larger than a testis, and broad caeca (see Caffara et al. 2011, 2014). This study contributes with the first report of a Clinostomum species in a South American anuran. Calhoun et al. (2020) in supplementary material present a reference, Castro-Tavernari et al (2009), as an anuran record for Chile but this reference concerns on fishes’ parasites from Brazil.