Mussel of the

Page last updated
9 September 2016

Mussel of the Month

The September 2016 Mussel of the Month is Glebula rotundata. Glebula is a monotypic genus from the southern United States.

Glebula rotundata
MNHN. Locality unknown. (type of Unio suborbiculata Lamarck, 1819)

Glebula belongs to a small group of monotypic genera that are largely restricted to the Gulf Coastal drainages of the United States (Graf & Cummings, 2007) — the others being Elliptoideus and Plectomerus. There are thirteen total monotypic genera in North America, 9 mostly in the in the interior basin (Dromus, Ellipsaria, Lemiox, Simpsonaias, Pegias, Obliquaria, Hemistena, Cyclonaias, Tritogonia) and Gonidea in the Pacific drainages. Cyclonaias may need to be sunk into Amphinaias, but the rest of these seem pretty taxonomically stable.

In some cases, we have been skeptical of monotypic genera. For example, the monotypic genus Arkansia was sister to the monotypic Arcidens. But why? In a case like that there is no distinction between the traits of the species and the traits of the genus. It leads to redundant taxonomy.

Glebula is recognized largely based on shell characters, though its soft anatomy is like other lampsilines (Simpson, 1914). Phylogenetic analyses have placed G. rotundata as sister to Cyrtonaias (Chapman et al., 2008; Pfeiffer et al., 2016).


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Family UNIONDAE Rafinesque, 1820
Subfamily AMBLEMINAE Rafinesque, 1820
Tribe LAMPSILINI Ihering, 1901

Genus Glebula Conrad, 1853

Species Glebula rotundata (Lamarck, 1819)

To find out more about Glebula and its taxonomy:
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