Mussel of the Month

This species was our Mussel of the Month back in 2015, but at that time we — and almost everyone else — called it Acostaea rivoli. However, we have recently dug into the issue and have become convinced that Mulleria is probably the correct genus name.

Férussac (1824) first introduced the name Mulleria and provided a description. However, he did not name the specimen that he had before him or provide a definitive locality. Erroneously, he assumed that it must have come from Africa or Madagascar since it looked so much like Etheria.

The type species was fixed by subsequent monotypy by Deshayes (1827) when he applied the name Mulleria rivoli to the specimen to which Férussac was referring in the Rivoli collection (ICZN Art. 69.3). Isaac Lea (1851) also gave a name for the Férussac specimen (Mulleria ferussacii), and various English authors called that same specimen Mulleria lobata (Gray, 1847 [as a nude name]; H. & A. Adams, 1857; Woodward, 1871).

More than two decades later, d’Orbigny (1851) described Acostaea guaduasana from the Rio Magdalena in Colombia. Everybody at the time —including Lea, the Adams brothers, and Woodward — recognized that Acostaea was a junior synonym of Mulleria. Since then, there has been no disagreement about this fact, the consensus has been that there is only a single species, and M. rivoli is the senior synonym.

So, then why has this species been called Acostaea rivoli in all the modern literature, including as a previous Mussel of the Month and in our own global checklist (Graf & Cummings, 2021)? Because Thiele (1934) claimed that Mulleria Ferussac, 1824 was a junior homonym of (and thus preoccupied by) Mülleria Leach, 1814, a nominal genus of amphipod crustaceans. However, ICZN Art. 32.5.2.1 says that ü automatically becomes a ue, and so Mulleria Ferussac, 1824 has no beef with Muelleria Leach, 1814.

While we are personally much attached to Acostaea d’Orbigny, 1851, it sure seems like Mulleria rivolii is the correct name for this freshwater mussel.