Mussel of the Month

Delphinonaias delphinulus is another one of those Central American mussels about which we know very little. That is about all we can say when we honor mussels from that part of world in our monthly showcase (e.g., Psorula, Sphenonaias).

Delphinonaias caught our eye because it has been so unambiguously classified as a lampsiline since Simpson (1900). Even Martens (1900) — who was apparently unaware that Simpson was simultaneously moving mussel generic classification into the modern era — placed those mussels in Unio (Metaptera). Metaptera is a Rafinesque name for the genus Potamilus (also a Rafinesque genus). Presumably, these early classifications with Lampsilis and Potamilus were based on the alate* shape of Delphinonaias, but we wondered if anyone has actually looked at the anatomy. Does Delphinonaias exhibit the characteristic traits of the Lampsilini, like the marsupium limited to a portion of each outer demibranch and capable of expansion when gravid and long-term brooding?

There really aren’t that many references that mention the classification of Delphinonaias, and our quick scan of those did not produce an explicit description of the anatomy of D. delphinulus or any congener. However, Goodrich & van der Schalie (1937) came close. They lumped D. delphinulus under Leptodea paludosa and stated,

“On the whole, this species has all the characters of a Leptodea, both in soft parts and in shell characters.” (p. 47)

Leptodea (also alate*) is a lampsiline. Frierson (1927) and Haas (1969) even arranged Delphinonaias as a subgenus of Lampsilis. We recognized Delphinonaias as a genus (Graf & Cummings, 2007), and we will continue to do that until we have some data to the contrary.

-----
* Alate refers to the presence of hinge wings.