Mussel of the

Page last updated
7 September 2023

Mussel of the Month

The December 2020 Mussel of the Month is Lasmigona subviridis. Lasmigona is a genus of eight species from eastern North America.

[We now refer to this species as Platynaias subviridis. — DLG 7 September 2023.]

USNM 86139. Neuse River, Raleigh, North Carolina (type of Unio pertenuis Lea, 1863).

This month, we feel like shaking things up. We are gonna freak out the (taxonomic) squares by playing fast and loose with nomenclature on the Internet. What’s up!?

Back in September 2012, we had designated Lasmigona complanata as MotM. Why circle back to a genus when there are still taxa we haven’t yet touched? We are coming back to Lasmigona before going completely around the world, but we suspect that our repeat selection may eventually be vindicated as prescient. We have needed frequently to retroactively revise the genus of a Mussel of the Month as taxonomy has shifted over the last decade and a half — e.g., Oxynaia jourdyi to Nodularia, Arconaia lanceolata to Lanceolaria, Fusconaia ebenus to Reginaia, Elliptio dilatata to Eurynia, Actinonaias ligamentina to Ortmanniana, Mweruella mweruensis to Prisodontopsis, Hyridella menziesii to Echyridella. This time, we are banking on it. L. subviridis is classified as Lasmigona now, but in this era of genus-splitting, we are forecasting that we will be ahead of the curve on this one when the dust settles.

The subgeneric classification of Lasmigona pre-dates Frierson (1914), but it was in that paper that the modern genus name took the place of Symphynota (which now is regarded as Potamilus). Walker (1918) came up with the subgenus Platynaias to fill the hole left by Symphynota. As Ortmann (1912, 1914) saw it, these American anodontines (triangular hooked-type glochidia, triapartite water-tubes, etc.) with hinge teeth could be arranged together and distinguished from Alasmidonta by their typically “not heavy”, frequently double-looped beak sculpture and tendency for the inner-most lamellae of the ctenidia to be free of the visceral mass.

The classification of the current species looks like this:

Lasmigona (Lasmigona) costata (Rafinesque, 1820) [type species]
Lasmigona (Ptyrosyna) complanata (Barnes, 1823) [type species]
Lasmigona (Ptyrosyna) alabamensis Clark, 1985

Lasmigona (Platynaias) compressa (Lea, 1829) [type species]
Lasmigona (Platynaias) decorata (Lea, 1852)
Lasmigona (Platynaias) subviridis (Conrad, 1835)

Lasmigona (Alasminota) holstonia (Lea, 1838) [type species]
Lasmigona (Alasminota) etowaensis (Conrad, 1849)

Clarke (1985) synonymized L. (Ptyrosyna) with Lasmigona (s.s.), and that relationship has been supported by the available phylogenetic analyses. When Lasmigona costata and L. complanata are in the same cladogram, they have been recovered together (e.g., King et al., 1999; Breton et al., 2011; Chase et al., 2018; but see Inoue et al., 2014). Where L. costata goes, so goes the name Lasmigona.

But, in these same studies, Lasmigona subviridis was recovered with L. compressa in a separate clade, often with Alasmidonta. Based on the work to-date, Lasmigona seems to span the breadth of the Alasmidontina (the subtribe of eastern North American anodontines). If we want natural, monophyletic taxa, these results suggest that either the concept of Lasmigona needs to be broadened to the point of meaninglessness or the genus will need to succumb to some splitting.

Fortunately, Walker (1918) has already given us a name. In that case, this month’s mussel would be called Platynaias subviridis. That is, unless Lasmigona holstonia is found in the same clade. In that case, according to Ortmann (1914), the name will be Alasminota subviridis. We look forward to learning which might be correct.


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Superfamily UNIONOIDEA Rafinesque, 1820
Family UNIONIDAE s.s.
Subfamily UNIONINAE s.s.
Tribe ANODONTINI Rafinesque, 1820
Subtribe ALASMIDONTINA Rafinesque, 1820

Genus Lasmigona Rafinesque, 1831

Species Lasmigona subviridis (Conrad, 1835)

To find out more about Lasmigona and the phylogeny of the Alasmidontina, check out:
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