Abstract
A new species of Rhopalias Stiles & Hassall, 1898 is described from the small intestine of the Common opossum, Didelphismarsupialis Linnaeus from the Yucatán Peninsula, Mexico. Rhopaliasoochisp. nov. is morphologically very similar to the type species of the genus, Rhopaliascoronatus (Rudolphi, 1819) Stiles & Hassall 1898, a species widely distributed in opossums across Mexico. A molecular phylogenetic analysis using a mitochondrial gene (cox1), and the nuclear ribosomal internal transcribed spacer region (ITS1-5.8S-ITS2), of specimens of R.coronatus collected in several localities of Mexico revealed that those from the Yucatán Peninsula, originally recorded on morphological grounds as R.coronatus actually represented an independent genetic lineage. Maximum Likelihood and Bayesian Inference analyses were performed for each data set independently, and for the concatenated data set (ITS1-5.8S-ITS2 + cox1). All phylogenetic analyses showed that the specimens from Yucatán represented a monophyletic lineage, with high bootstrap support and Bayesian posterior probabilities. In addition, the genetic divergence estimated between R.oochisp. nov. and two species of Rhopalias, R.coronatus, and R.macracanthus Chandler, 1932 that also occur in Mexican marsupials ranged between 7–8% and 16–17%, for cox1, and between 0.1–0.2% and 7% for the ITS region, respectively. The molecular evidence gathered in this study (reciprocal monophyly in both phylogenetic analyses, and estimated genetic divergence) suggested that the specimens found in the intestine of D.marsupialis originally reported as R.coronatus from Yucatán, actually represent a new species. Morphological evidence was found through light and scanning electron microscopy to support the species distinction based on molecular data.
Highlights
The genus Rhopalias Stiles & Hassall, 1898 includes six species of digenetic trematodes that infect the small intestine of didelphimorph marsupials of the New World (Haverkost and Gardner 2008)
Molecular data were used in combination with a morphological study of newly sampled specimens of R. coronatus, and those deposited at the Colección Nacional de Helmintos (CNHE) to describe a new species of Rhopalias
Clade I, corresponding to R. coronatus according to their morphology, included 101 sequences from six localities: 26 isolates from Los Tuxtlas (LT), isolates from Tlacotalpan (TL), from Soyoltepec (SO), 39 from Agua Fría
Summary
The genus Rhopalias Stiles & Hassall, 1898 includes six species of digenetic trematodes that infect the small intestine of didelphimorph marsupials of the New World (Haverkost and Gardner 2008) Members of this genus of echinostomatid trematodes (see Tkach et al 2016) are distinguished by having two anterior tentacles armed with spines, which can be invaginated into a muscular pouch, one on each side of oral sucker (Kostadinova 2005). In a taxonomic review of the species of the genus Rhopalias, Haverkost and Gardner (2008) discussed the morphological characters that could be used for distinguishing among congeneric species, concluding that the number and size of tentacle spines, the presence or absence of oral and/or flanking spines, and the length of the muscular pouches are the most reliable characters.
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