Heterophyidae

Scholz, T., Aguirre-Macedo, M. L. & Salgado-Maldonado, G., 2001, Trematodes of the family Heterophyidae (Digenea) in Mexico: a review of species and new host and geographical records, Journal of Natural History 35 (12), pp. 1733-1772 : 1767

Heterophyidae gen. sp. of Scholz et al. (1995)

This metacercaria apparently belonged to a species of the Ascocotyle -complex because of the presence of a complete row of circumoral spines, most probably to A. (L.) nunezae . However, this species possesses additional spines on the dorsal spines and its metacercariae encyst exclusively in the gills.

Despite a relatively high number of taxa reported from Mexico, further heterophyid trematodes may still be found in Mexico. There are several species such as Ascocotyle (Ascocotyle) pachycystis Schroeder and Leigh, 1965 ; A. (A.) puertoricensis Price, 1932 ; A. (A.) sexidigita Miller and Harkema, 1962 ; A. (P.) mollienisicola Sogandares-Bernal and Bridgman, 1960 ; or species of Galactosomum , that occur in the neighbouring countries, especially in the southern part of the USA (Florida, Louisiana, Mississippi) ( Price, 1932, 1935; Sogandares-Berna l and Bridgman, 1960; Miller and Harkema, 1962; Hutton, 1964; Schroeder and Leigh, 1965; Yoshino, 1972).

As demonstrated by Ostrowski de NuÂnÄez (1993), Scholz et al. (1997a), Scholz (1999) and in this study, the number of circumoral spines may be very constant and species-speci®c. However, this is valid mainly for those taxa that possess a relatively low number of spines such as A. (P.) angrense (181 2), A. (P.) diminuta (161 2), A. (P.) longa (16), A. (P.) macrostoma (18) or A. (A.) tenuicollis (161 16). In contrast, the number of spines may be subjected to some intraspeci®c variation in the species that have higher number of spines such as A. (L.) megalocephala (36±40 in one row), A. (L.) mcintoshi (19±21 in one row) and A. (L.) nunezae (25±261 6±10).

Species of the Ascocotyle -complex represent the dominant group of heterophyids in Mexico but their subgeneric classi®cation is unsatisfactorily resolved and a new arrangement should be proposed. However, such an arrangement requires a phylogenetic analysis of the group which will be possible only after more complete data on the morphology of individual species and their developmental stages, including cercariae, are available. Because of the existence of sibling species among heterophyids in North and South America ( Font et al., 1984a; Ostrowski de NuÂnÄez, 1992, 1996), life-cycle studies should be carried out and more thorough descriptions of the morphology of metacercariae and adults of many taxa should be provided. Current classi®cation, largely based on the topography of female genital organs (vitelline follicles, uterine loops) and the number of rows of circumoral spines, is apparently arti®cial and several species present intermediate characters which do not allow their placement within well-de®ned taxonomic entities.