Calhoun, Dana Marie (2011-05). A Reevaluation of the Taxonomy of the Mesocoelium monas Complex (Platyhelminthes: Digenea: Mesoceliidae). Master's Thesis.
Specimens from the National History Museum, London, and from the United States National Parasite Collection, Beltsville, United States of America., which had all previously been identified as Mescoelium monas from a variety of definitive hosts (amphibians, reptiles and/or fish), were evaluated using all available literature and the body-type keys developed by Norman Dronen. None of these 85 putative M. monas specimens appeared to fit the original description of M. monas. There are likely multiple species of Mescoelium worldwide, and the M. monas complex, as currently defined, is not a unified monospecific grouping. The present study leads to the conclusion that there can be no fewer than 9 species of Mescoelium (6 body types, 3 of which can be divided into 2 separate groups based on the median or submedian placement of the genital pore). The specimens of M. monas I examined represented 3 of the 6 body types identified by Norman Dronen: the M. monas body type, the M. lanceatum body type, and the M. pesteri body type. Because Mesocoelium is a difficult group within which to distinguish species, it may be expedient in endoparasitic surveys of amphibians, fish and reptiles to consider any specimen of Mesocoelium found to be M. monas. Because Mesocoelium is a difficult group within which to distinguish species, it may be expedient in endoparasitic surveys of amphibians, fish and reptiles to consider any specimen of Mesocoelium found to be M. monas. Subsequent reevalations must consider these key characteristics: genital pore placement, cecal length, vitelline follicle distribution, along with other supporting characteristics.