Mussel of the Month

Cyclonaias tuberculata is a rather distinctive mussel species for its combination of warty sculpture and colored nacre. It’s a good-looking shell. However, classification of this species has been trouble from the get-go, and it is likely that during the next round of generic revisions, Cyclonaias will be replaced with Amphinaias or maybe Rotundaria. It is kind of a long story, so get a beverage and make yourself comfortable.

Going into the 20th century, this freshwater mussel went by the name Rotundaria tuberculata. Rafinesque (1820)* described Obliquaria (Rotundaria) with three included species: O. tuberculata, O. subrotunda (= Obovaria subrotunda), and O. pusilla (= Fusconaia ebena?). O. tuberculata was listed first, and, by the nomenclatural standard applied by Simpson (1900) and others, that was good enough to regard it as the type species — though it was never explicitly designated by Rafinesque.

However, Ortmann & Walker (1922) discovered that Herrmannsen (1848) had been explicit in listing O. subrotunda as the type of Rotundaria, and they accepted that as a subsequent designation of the type species. Thus, Rotundaria became a junior synonym of Obovaria (also named by Rafinesque), and Ortmann & Walker (1922) did their best to resolve the problem by taking the name Cyclonaias from their friend Henry Pilsbry. Since 1922, the name has been Cyclonaias tuberculata.

A new wrinkle with the nomenclature of C. tuberculata came from Campbell & Lydeard (2012) when they reported that Valenciennes (1827) had selected O. tuberculata as the type of Rotundaria. However, that is not exactly what Valenciennes said. Here is the full quote referred to by Campbell & Lydeard (they only quoted the bold-faced part):

“Nous avons reçu au cabinet du Roi une autre Mulette remarquable par sa forme arrondie, et par les nombreux tubercules dont sa surface est couverte. M. Rafinesque l'a envoyée comme le type d'un nouveau genre qu'il nomme Rotundaria. Les dents de la charnière sont disposées exactement comme celles des Mulettes. Ainsi nous croyons devoir laisser cette coquille dans le genre Unio; et, en donnant la description et la figure de cette espèce remarquable, nous aurons encore occasion d'en séparer deux qui ont été confondues en une seule: elles viennent de l'Ohio. Je laisserai à l'une d'elles le nom sous lequel M. Rafinesque nous a envoyé les deux espèces, et je la caractériserai par la diagnose suivante.”

Valenciennes received more than one shell from Rafinesque belonging to two different species. One he did refer to as Unio tuberculata (not subscribing to Rafinesque’s genus), but the other he named U. verrucosa non Barnes (= Amphinaias pustulosa). Notice that Valenciennes did NOT explicitly say “tuberculata is the type of Rotundaria.” The whole sentence in the bold-faced part of the quote basically reported that Rafinesque sent him shells that Rafinesque called the type of Rotundaria. But, Valenciennes referred to that “type” as two different species. Moreover, Valenciennes listed his new species first, and that was the one that he figured. This sort of fuzziness is not the kind of data on which to base nomenclature, but we concede that while we haven’t seen the fire yet, there is smoke.

After this long tale, you may be thinking, “Who cares?” (You may have screamed it out loud before clicking back to a web page in which you are interested.) Why would anyone get so cranked up about the unconfusing nomenclature of one species? The vexing issue is that phylogenetic studies have nested C. tuberculata in a clade with species of Amphinaias Crosse & Fischer, 1894 (e.g., A. pustulosa) (Boyer et al., 2011; Campbell & Lydeard, 2012). In this taxonomic twilight zone, Cyclonaias tuberculata should be Amphinaias tuberculata, but if it is Rotundaria tuberculata then all species currently classified as Amphinaias should also be transferred to Rotundaria! Or they are all just Quadrula (also named by Rafinesque)... **

It is a crazy world. Someone should sell tickets.

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* From the mention of that name, you know this story is going to be more complicated than it is worth.

** We have discussed the lumping/splitting of Quadrula with previous Mussels of the Month Quadrula quadrula and Theliderma cylindrica.