Ascocotyle (A.) nunezae n. sp. (Digenea: Heterophyidae) from Yucatan, Mexico

A new heterophyid species, Ascocotyle (Ascocotyle) nunezae n. sp., is described from adults found in the intestine of naturally infected heron, Casmerodius albus (type host), from the coastal lagoon of Celestdn, Yucatan, Mexico, and a domestic chick (Gallus gallus), experimentally infected with metacercariae from Cichlasoma octofasciatum. The new species is character- ized mainly by the number (32-37) and arrangement of circumoral spines, which form 1 complete row of 25-27 circumoral spines and 6-10 accessory spines on the dorsal side, and by the morphology of the ventrogenital sac with a large gonotyl, consisting of 2 indistinctly separated lobes of vesicular tissue. Ascocotyle (A.) nunezae is placed into the nominotypical subgenus Ascocotyle because of the presence of uterine loops at the pharyngeal region and position of vitelline follicles. However, it differs distinctly from other members of this subgenus by the presence of long intestinal ceca reaching posterior to the ventral sucker. Cichlids of the genus Cichlasoma from cenotes, lakes, and the river Rifo Hondo in the Yucatan Peninsula were natural second intermediate hosts of A. (A.) nunezae, with metacercariae encysted on their gills. Cichlasoma meeki (Brind) was the most heavily infected fish host (total prevalence 75%; mean intensity 11 ? 9). Heterophyid metacercariae, designated as Ascocotyle (Phag- icola) sp. 3 by Scholz et al. (1995a), were found in the gills of cichlids of the genus Cichlasoma Swainson, 1839 during a study on the parasites of fish from cenotes (=sinkholes), small water bodies in the Peninsula of Yucatan, Mexico (Scholz et al., 1995b). Morphological studies of adult trematodes found in a naturally infected heron, Casmerodius albus (L.), and adults recovered from a domesticated chick, experimentally infected with these metacercariae, revealed that they represented a new, hitherto undescribed species of the genus Ascocotyle Looss, 1899. This species, for which the name Ascocotyle (Ascocotyle) nunezae is proposed, is described in the present paper.