Systematics of Mexiconema cichlasomae (Nematoda: Daniconematidae) based on sequences of SSU rDNA.

The molecular characterization of the daniconematid dracunculoid Mexiconema cichlasomae Moravec, Vidal, and Salgado-Maldonado, 1992 through the sequencing of SSU rDNA from adult individuals is presented herein. Additionally, preliminary genetic relationships of this nematode are inferred from alignment of sequences generated previously for other dracunculoids. Maximum parsimony and maximum likelihood analyses recovered identical trees. As anticipated by previous taxonomic work, M. cichlasomae is putatively closely related to skrjabillanid dracunculoids represented by Molnaria intestinalis (Dogiel and Bychovsky, 1934) and Skrjabillanus scardinii Molnár, 1966 SSU rDNA sequences, but the relationships of this newly discovered clade to other dracunculoid clades remain unresolved.

The systematic position of Wallinia spp. and Margotrema spp. (Digenea), parasites of Middle-American and Neotropical freshwater fishes, based on the 28S ribosomal RNA gene.

The systematic relationships of aspinose allocreadiid-like digeneans from Middle-American and Neotropical freshwater fishes, such as Wallinia Pearse, 1920, Margotrema Lamothe-Argumedo, 1970, Magnivitellinum Kloss, 1966 and other related genera, remain enigmatic. Wallinia (2 spp.) and Margotrema (2 spp.) have been placed in the subfamily Walliniinae, within the Macroderoididae. Recent descriptions of species in these genera have followed this classification but have raised questions about their affinities with macroderoidids. Partial sequences of the 28S rRNA gene of Wallinia chavarriae Choudhury, Hartvigsen & Brooks, 2002 and Margotrema bravoae Lamothe Argumedo, 1970, as representatives of their genera, were used in a phylogenetic analysis along with the available sequences of macroderoidids and allocreadiids. Results from Maximum Parsimony, Maximum Likelihood and Bayesian Analyses were identical in placing both genera into one clade along with allocreadiids rather than the macroderoidids. Margotrema was the sister group of Crepidostomum Braun, 1900, and Wallinia was the sister group of both Margotrema and Crepidostomum combined. Bootstrap and Bremer values, as well as posterior probabilities derived from Bayesian analysis strongly supported these relationships in three analyses.

Molecular phylogeny of clade III nematodes reveals multiple origins of tissue parasitism.

Molecular phylogenetic analyses of 113 taxa representing Ascaridida, Rhigonematida, Spirurida and Oxyurida were used to infer a more comprehensive phylogenetic hypothesis for representatives of 'clade III'. The posterior probability of multiple alignment sites was used to exclude or weight characters, yielding datasets that were analysed using maximum parsimony, likelihood, and Bayesian inference methods. Phylogenetic results were robust to differences among inference methods for most high-level taxonomic groups, but some clades were sensitive to treatments of characters reflecting differences in alignment ambiguity. Taxa representing Camallanoidea, Oxyurida, Physalopteroidea, Raphidascarididae, and Skrjabillanidae were monophyletic in all 9 analyses whereas Ascaridida, Ascarididae, Anisakidae, Cosmocercoidea, Habronematoidea, Heterocheilidae, Philometridae, Rhigonematida and Thelazioidea were never monophyletic. Some clades recovered in all trees such as Dracunculoidea and Spirurina included the vast majority of their sampled species, but were non-monophyletic due to the consistent behaviour of one or few 'rogue' taxa. Similarly, 102 of 103 clade III taxa were strongly supported as monophyletic, yet clade III was paraphyletic due to the grouping of Truttaedacnitis truttae with the outgroups. Mapping of host 'habitat' revealed that tissue-dwelling localization of nematode adults has evolved independently at least 3 times, and relationships among Spirurina and Camallanina often reflected tissue predilection rather than taxonomy.

A new rhabdochonid from the blue striped chub Sectator ocyurus (Osteichthyes: Kyphosidae) in Chamela Bay, Mexico.

Megachona chamelensis n. gen., n. sp. is described from the intestinal cecae of blue striped chub Sectator ocyurus (Kyphosidae, Perciformes), from Chamela Bay, Mexico. Megachona n. gen. most closely resembles Beaninema Caspeta-Mandujano, Moravec, and Salgado-Maldonado, 2001; Fellicola Petter and Køie, 1993; and Rhabdochona Railliet, 1916. The main characters that distinguish the new genus from all other rhabdochonids include a longer than wide funnel-shaped prostom and cuticular longitudinal ridges of prostom forming anteriorly subterminal massive toothlike structures followed posteriorly by irregularly arranged smaller teeth. This finding brings the total number of genera of Rhabdochonidae of marine fish in Mexico to 2. The new species is characterized by having a smaller number of cuticular longitudinal ridges in the male prostom than in the female prostom, forming massive toothlike structures in its subterminal portion, followed by more minute teeth in the female than in the male, a slender tail end with a broad tip, the distal part of the left spicule with a lanceolate end, a straight right spicule without a dorsal barb, 1 pair of precloacal and 3 pairs of postcloacal papillae, and a smooth egg surface.

Phylogeny and biogeography of Rhabdochona Railliet, 1916 (Nematoda: Rhabdochonidae) species from the Americas.

A phylogenetic analysis of 40 species of Rhabdochona Railliet, 1916, including all 21 valid species in the Americas, resulted in 1733 equally most parsimonious trees and indicates that Rhabdochona is arguably monophyletic. Species from the Americas do not form a monophyletic group, since each of the six clades of Rhabdochona includes species from the Americas and species from other continents. The synapomorphies defining each clade stem from the morphology of the left spicule. Teeth number was consistent in one clade only, suggesting that this character, while useful for taxonomic purposes, is not indicative of phylogeny. Species of Rhabdochona associated with certain host groups, such as salmonids, catostomids and goodeids, do not always form monophyletic assemblages, nor do species associated with smaller discrete areas, such as the Mesa Central of Mexico. This indicates widespread host-switching rather than co-speciation as the main phenomenon in the evolution of this group, at least in the species from the Americas. Phylogenetic patterns reveal an ancient origin for the group that probably pre-dates current continental configurations.

Rhabdochona ahuehuellensis n. sp. (Nematoda: Rhabdochonidae) from the Balsas goodeid, Ilyodon whitei (Osteichthyes: Gooedeidae), in Mexico.

Rhabdochona ahuehuellensis n. sp. is described from the Balsas goodeid, Ilyodon whitei. The distinctive characters are cuticular elevations in the middle of the prostom, tricuspid ending of the distal part of the left spicule combined with a scoop shape, and an egg surface with limited, short subpolar filaments. The characters place the present species farther apart from species described from North America, except R. lichtenfelsi. This description brings the total number of species of Rhabdochona in the Mesa Central of Mexico to 4, suggesting that this genus has undergone speciation in response to basin fragmentation within the Mesa Central of Mexico.