The Neotropical freshwater mussel fauna played an important role in the evolution of the current taxonomy of the order Unionoida, especially the family Hyriidae. That family was at the intersection of a taxonomic argument that spanned almost a century regarding the higher classification of freshwater mussels — What are the relationships among the families? Or, to put it another way, how do we arrange the families into superfamilies?
In the pre-cladistic era, Ortmann (1921; the last genius to work on mussel systematics) placed the Hyriidae in a superfamily with the Iridinidae and Mycetopodidae* based on shared characteristics of their adult anatomy. For example, all of these mussels brood their larvae in the inner demibranchs of their ctenidia (= gills), have their posterior mantle margins fused between the incurrent and excurrent apertures, and have a wide separation between the anterior attachment of the inner demibranchs and the labial palps. Species of the Unionidae and Margaritiferidae brood in the outer pair of demibranchs or all four (or rarely only the inner pair), the posterior mantle lobes are never fused, and the inner demibranchs attach adjacent to the labial palps.†
In contrast, Parodiz & Bonetto (1963) grouped the Hyriidae with the Unionidae and Margaritiferidae based on larval characteristics: All three families have glochidia while the Iridinidae, Mycetopodidae, and Etheridae all have lasidia instead. Both glochidia and lasidia are parasitic larval stages, although they have strikingly different morphologies.†
For those of us working in the era of modern systematic biology, these pre-cladistic, authoritarian classifications have value as hypotheses to be tested and as inspiration for the kinds of characteristics we should be looking at. Among the earliest relevant analyses, Graf’s (2000) phylogenetic analysis of mussel morphology (adult and larval) favored Ortmann’s system, Bogan & Hoeh’s (2000) study applying nucleotide characters supported a novel set of relationships with the Hyriidae sister to the five other families, and little support was found for Parodiz & Bonetto’s (1963) classification.‡
Skip to 2016, and there are considerably more data on the higher classification of the Unionoida and the phylogenetic position of the Hyriidae. The most comprehensive treatment to-date was published last year by Graf et al. (2015), finding strong support for the monophyly of the Hyriidae and pretty good (but not great) support for Hyriidae as sister to all the other families. Nowadays, we recognize three superfamilies of freshwater mussels:
- Hyrioidea = Hyriidae,
- Unionoidea = Unionidae + Margaritiferidae, and
- Etherioidea = Iridinidae + Etheriidae + Mycetopodidae.
This stroll down classification-history lane was prompted by the recent article by Santos-Neto et al. (2016). Whereas Graf et al. (2015) focused on the Australasian hyriid lineages, this newer paper has the broadest taxon sampling yet from South America, including Callonaia.
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* Actually, Ortmann classified what we now call the Hyriidae, Iridinidae, and Mycetopodidae into a single family with two subfamilies: Mutelidae (= Etherioidea), with Hyriinae (= Hyriidae) and Mutelinae (= Iridinidae + Mycetopodidae). At the time, etheriids weren't really a part of his world-view of freshwater mussels.
† See Graf & Cummings (2006) for a detailed explanation of these technical mussel characteristics.
‡ When DLG presented his results at the 1999 meeting of the American Malacological Society in Pittsburgh, Juan Parodiz monopolized the entire question period with a vigorous argument in favor of the Bonetto & Parodiz classification. | 
