Mussel of the

Page last updated
1 December 2014

Mussel of the Month

The December 2014 Mussel of the Month is Inversiunio reinianus. Inversiunio is a genus of four species found in Japan and Korea.

Inversiunio reinianus
SMF 3645. Lake Biwa, Japan (type)

Back in October 2009, we discussed the problem of Inversidens sensu lato. In Haas's (1969) conchological view, that genus was composed of 6 species from eastern Asia and Japan. However, it was subsequently discovered that two different larval morphologies were represented among those species. Whereas as shell morphology (outline, umbo position, sculpture, etc.) is highly variable, often convergent, and well known to confound a natural classification, structures of glochidium-type larvae can be downright diagnostic.

In the the particular case of Inversidens sensu lato, some species (e.g. I. brandtii) have glochidia lacking marginal hooks. That doesn't tell us much about classification since most unionid freshwater mussels have unhooked type glochidia. But, other species (like I. reinianus) have glochidia with marginal hooks. In the family Unionidae, only members of the subfamily Unioninae have hooked-type glochidia. Thus, Inversidens sensu lato was composed of representatives of (at least) two different subfamilies. To solve this problem, the genus Inversiunio in the subfamily Unioninae was created (Habe, 1991). Inversidens is currently placed in the Gonideinae.

The separation of Inversidens sensu stricto and Inversiunio based on their divergent larval morphologies is not an isolated case. An analogous situation has also occurred with certain species formerly of the genus Lamprotula (also Gonideinae) being transferred to Aculamprotula (Unioninae) because of their hoooked-glochidia.


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Family UNIONIDAE Rafinesque, 1820
Subfamily UNIONINAE s.s.
Tribe UNIONINI s.s.

Genus Inversiunio Habe, 1991

Species Inversiunio reinianus (Kobelt, 1879)

To find out more about Inversiunio and the freshwater mussels of eastern Asia, check out:
  • Haas, F. 1969. Superfamilia Unionacea. Das Tierreich 88: 1-663.
  • Habe, T. 1991. Catalogue of non-marine molluscs in Japan. Hitachiobi 56: 3-7.
  • Kondo, T. 2008. Monograph of Unionoida in Japan (Mollusca: Bivalvia). Special Publication of the Malacological Society of Japan (3): 69 pp.
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