The validity of Genolopa Linton, 1910 has been controversial because the observation of presently recognized critical diagnostic morphological features (spines in the genital atrium and a bipartite, anteriorly spined terminal organ) were omitted from the original diagnosis, and these features were not universally appreciated as important diagnostic features until 2008. Modern taxonomists have been further challenged by inappropriate fixation techniques that have resulted in various interpretations of morphological features. Consequently, named species in the genus have fluctuated among other monorchiid genera depending on various interpretations by taxonomists, and a modern consensus on classifying these species is lacking. This study combines a molecular approach with modern conventional morphological techniques to investigate the validity of Genolopa as a lineage within the Monorchiidae. New morphology and molecular sequence data from the type-species of Genolopa were studied, and two new species in the genus were described, Genolopa vesca n. sp. and Genolopa minuscula n. sp. Interrelationships among the Monorchiidae were explored using Bayesian inference analysis of the partial 28S rDNA fragment, incorporating three species of Genolopa for the first time. The phylogenetic analysis revealed that the genus represents a natural lineage, supporting the presence of spines in the genital atrium in conjunction with a bipartite and anteriorly spined terminal organ as key features of the generic diagnosis. This study also provides for the first time partial 28S rDNA data for Postmonorchis orthopristis, Lasiotocus trachinoti, Lasiotocus glebulentus, and an unidentified species of Lasiotocus.
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