Redescription of Perezitrema bychowskyi (Caballero & Caballero, 1975) (Trematoda: Macroderoididae), with remarks on the systematic status of Perezitrema Barus & Moravec, 1996.

A description is given of Perezitrema bychowskyi (Caballero & Caballero, 1975) based on newly collected specimens from the intestine of the tropical gar Atractosteus tropicus Gill in the Pantalos de Centla Biological Reserve, State of Tabasco, southeastern Mexico, collected in April 2001, and on a re-examination of the type-specimens. In contrast to the original description, the excretory vesicle of P. bychowskyi was found to be elongate saccular and the intestinal caeca join near the posterior extremity and open via a common median anus. These features, and the presence of a cirrus-sac, were found, using differential interference contrast optics in the type-specimens of P. viguerasi Barus & Moravec, 1967, the type-species of the genus. This made possible a re-diagnosis of Perezitrema Barus & Moravec, 1967. Although P. bychowskyi is very similar to P. viguerasi and their conspecificity cannot be excluded, the poor condition of the type-specimens of the latter does not enable their detailed comparison and, consequently, both are considered independent species for the time being. P. lepisostei (Watson, 1976) is considered a junior synonym of P. bychowskyi. Perezitrema is provisionally placed in the plagiorchioid family Macroderoididae, even though some of its morphological features are similar to those of the lepocreadioid families Enenteridae and Lepocreadiidae.