Redescription and new records of Polymorphus trochus (Van Cleave, 1945) (Polymorphida: Polymorphidae), in Mexico.

Polymorphus trochus Van Cleave, 1945, is an acanthocephalan with limited distribution to the Americas and a common parasite of birds of the Rallidae family (Kinsella et al. 1973, McDonald 1988 and Amin 1992), mainly of the American coot Fulica americana Gmelin, 1789; however, despite existing records of this species, the knowledge and descriptions of its morphological characteristics are not sufficient. Therefore, the identification of this species can be confusing, particularly because it depends on the form of the proboscis of the female. Van Cleave (1945) provided a description and illustrations of this species based on 14 females and 2 males specimens collected in the intestine of F. americana from Lake Buckeye in Ohio, Lake Oneida in New York, and the Illinois River in Illinois; however, this description does not mention many traits that are taxonomically important. Years later, Nickol (1966, thesis not published) provided a description of P. trochus based on 36 mature specimens (14 females and 22 male) from Louisiana, but the author illustrated only the proboscis and included a schematic of the female. He described the shape and size of the proboscis in both sexes, provided measurements of the apical, middle and basal hooks of the proboscis armor, and measurements of the eggs. However, he did not mention the exact distribution of the hooks and spines of the trunk, the measurement of a complete row of hooks nor the shape of all the sexual organs, especially the female ones, which are important taxonomic characteristics in the polymorphids.

Larval stages of trematodes in gastropods from Lake Chicnahuapan, State of Mexico, Mexico.

During the period from January to December (2007), 1,095 freshwater molluscs of four species were captured (Lymnaea stagnalis, Stagnicola elodes, Physella cubensis and Physa acuta) in Lake Chicnahuapan, State of Mexico, Mexico. Two hundred seventy-two (24.84% prevalence) of these molluscs were parasitised by 11 trematode species (from which two were not identified at the species level) having six cercariae species and five metacercariae species represented in five families. The cercariae Telorchis corti (Plagiorchiidae) and the metacercariae Cotylurus cornutus (Strigeidae) were the species with the highest prevalence among the examined snails. The highest percentage of infection was observed in L. stagnalis (27.45% of prevalence, n = 572) and P. cubensis (23.96%, n = 455). Twenty-one of the examined snails had multiple infections with up to three trematode species.

Helminth parasites of Girardinichthys multiradiatus (Pisces: Goodeidae) in the upper Lerma River sub-basin, Mexico.

Thirteen helminth species were recorded during a helminthological examination of 754 Girardinichthys multiradiatus (Meek) (Pisces: Goodeidae) collected from 20 localities in the upper Lerma River sub-basin on the highland plateau of Mexico. The study constitutes a complete and extensive inventory of the helminth parasites of this freshwater fish species across its entire current geographic distribution. The collected species included one adult trematode, three metacercariae, one monogenean, one adult cestode, three metacestodes, three nematode larvae and one cystacanth. The records of the metacercariae of Tylodelphys sp. and Ochetosoma brevicaecum, the larvae of the nematodes Contracaecum sp. and Falcaustra sp. and the cystacanth of Polymorphus brevis are all new records for G. multiradiatus. The metacercariae of Tylodelphys sp. were the most widespread and prevalent species in the sample, being collected from 15 of the 20 sampling localities, with a prevalence of 3.2-72.2%. The data indicate the helminth parasite community of G. multiradiatus to be relatively poor when compared with the helminth communities of freshwater fish from other parts of Mexico. This community is subject to colonization by generalist helminth species, mostly transported by birds. A further component of this community consists of helminth species that have been introduced anthropogenically.

Helminth parasites of the tropical gar, Atractosteus tropicus Gill, from Tabasco, Mexico.

A total of 8 helminth species were recorded in an examination of 43 tropical gar, Atractosteus tropicus Gill, collected at the Pantanos de Centla Biosphere Reserve, Tabasco, Mexico. The parasite species included 1 adult trematode, 3 metacercariae, 1 cestode, 1 adult nematode, and 2 nematode larvae. Six of these 8 species were rare, with low prevalence (< 17%) and abundance (< 1.0 helminths per examined fish). The larvae of Contracaecum sp. were the most abundant in the sample, constituting 60% of the total helminths (64% prevalence, 3.8 +/- 5.2 abundance), followed by the cestode Proteocephalus singularis, constituting 18% of the worms (30.5% prevalence, 1.1 +/- 3.0 abundance). Species richness, individual parasite abundance, and diversity were low in the infracommunities. The recording of 3 specialist species in the tropical gar confirms that the helminth fauna of gar has an appreciable degree of specificity. This study indicates the importance of ecological determinants of richness in helminth communities of the tropical gar.