Mussel of the

Page last updated
10 March 2023

Mussel of the Month

The August 2022 Mussel of the Month is Arcuneopsis pisciculus. Arcuneopsis is a monotypic genus endemic to China.

[The correct name for this mussel is Tchangsinaia piscicula since Tchangsinaia Starobogatov, 1970 is the senior synonym of Arcuneopsis Huang, Dai & Wu in Wu et al., 2022. — DLG 10 March 2023.]

ZMB_31062. Siang Kiang Fl., Prov. Hunan, China. (type of Unio retortus Martens 1875)

Until this year, this Mussel of the Month was classified in the genus Cuneopsis. But, in a phylogenetic study by Wu et al. (2022), the old Cuneopsis was split into three genera: Cuneopsis s.s., Pseudocuneopsis (for P. capitatus), and Arcuneopsis (for P. pisciculus). The latter two genera were introduced in the same work. The "twisty" morphology of the shell is convergent with Lanceolaria laneolata, but instead of dwelling on the (syn)apomorphies of Arcuneopsis, we would rather talk about how this web site is useful for evaluating the phylogenetic data that got us to this new, monotypic genus.

The Cladomics feature of the MUSSEL Project Web Site is a useful tool to explore the phylogenetic results obtained by different studies. We have recently updated and improved those pages. For all freshwater mussel taxa that have been included in a cladogram, we have endeavored to record the topologies. The “cladome” is the set of all published clades, and these have been integrated with the taxonomy presented on this web site. For any taxon — such as Arcuneopsis — users can see the various results from studies that have analyzed the relevant species. Rather than showing the whole cladogram, the cladomics pages show the parts of many (if not all) cladograms so that the relevant ingroup branches can be compared. We have recently expanded that feature to expand the trees to include a couple outgroup branches, so even a monotypic taxon like Arcuneopsis is shown anchored on a branch in the freshwater mussel tree. For example, here is one of the Arcuneopsis trees from Wu et al. (2022).

Wu et al. 2022 Arcuneopsis tree

Because the taxonomy is wired into the MUSSELpdb, the nomenclature of the terminal branches stays current as well. For example, Lopes-Lima et al. (2020) published a comprehensive phylogeny of East Asian freshwater mussels, including Arcuneopsis pisciculus. Of course, a name from 2022 didn’t exist then, but the tree reflects the update.

Lopes-Lima et al. 2020 Arcuneopsis tree

Moreover, analysis of our cladomics data set shows that the Lopes-Lima et al. (2020) phylogeny is a more comprehensive analysis of the phylogenetic position of Arcuneopsis, owing to the greater number of potential outgroups (among other criteria). For any taxon represented in the MUSSELpdb cladome, the “best” cladograms (according to how rigorously they test monophyly and the diversity of sampled outgroup taxa) are at the top of the list. The monophyly of a monotypic genus like Arcuneopsis isn’t that interesting, but the Lopes-Lima et al. (2020) is ranked best for sister taxa because that study sampled the most genera of the Unionini (9, “roS”) and did it first.

The various statistics that are used are explained on the Cladomics FARQ page. Feel free to click around and explore the diversity of the cladome to-date!


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

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

Genus Arcuneopsis Huang, Dai & Wu in Wu et al., 2022

Species Arcuneopsis pisciculus (Heude, 1874)

To find out more about Arcuneopsis and Cuneopsis, check out:

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