The May 2026 Mussel of the Month is Pseudodon mekongi
At least, that is what it is called today
Mussel taxonomy these days relies on the identifications of DNA sequences on GenBank, but those IDs are notoriously inaccurate. The MUSSEL Project Database (MUSSELpdb) can help with that.
For the uninitiated, GenBank refers to the nucleotide database of the NIH’s National Center for Biotechnology Information (NCBI). Since the 1980s, whenever scientists want to make DNA sequences of specific genes, chromosomes, or genomes publicly available, those data are deposited in GenBank. Each accession is assigned a unique identifier and annotated with its “source” and “features” — e.g., classification, authors, original publication, gene, voucher specimen, locality, protein translation, etc.
GenBank Accession KP795029 is currently identified in the freshwater mussel literature as Mussel of the Month Pseudodon mekongi. That COI sequence is meaningful (at least somewhat) because it has gone by more genus-species combinations than any other such sequence — at least according to my back-of-the-envelope analysis. It was originally identified by Pfeiffer & Graf (2015) as Pseudodon vondembuschianus, but it also has been called Pseudodon vondembuschianus laosica, it was classified in the genus Monodontina for a stint, and it has passed through various other binomials and trinomials before landing back in Pseudodon as P. mekongi (Zieritz et al., 2026). The data about KP795029 can be found on its Genbank Accession Page of the MUSSELpdb, shown below.
The identification of specimen KP795029 owes its opportunities for revision to its inclusion in so many phylogenetic studies. The tribe Pseudodontini has been an active target of taxonomic attention. Moreover, that sequence is a popular choice in such analyses because the same voucher specimen (UMMZ 304650) has been sequenced for COI, 16S, and 28S — the long-applied trifecta combining mitochondrial and nuclear markers for resolving freshwater mussel inter-generic relationships.
Re-identification of GenBank accessions is a general issue complicating the phylogenetic results that are the foundation of freshwater mussel taxonomy. For example, in the 11 years since Pfeiffer & Graf (2015) published KP795029, every one of the five samples then-classified as Pseudodon species in that analysis has been re-identified or revised. The specimen we called P. vondembuschianus is now Mussel of the Month Pseudodon mekongi, what was P. cambodjensis is now considered the real P. vondembuschianus (KP795028), and the other three have been dispersed into distinct genera that were not in use at the time: Bineurus, Nyeinchanconcha, and Sundadontina. That decade of taxonomic progress is evident in the comparison below of the entry for Pfeiffer & Graf (2015: fig. 2) on the MUSSELpdb Pseudodon Cladomics Page with the corresponding branch of the published tree.
The problem — we’re finally getting to the problem — is that GenBank doesn’t keep track of updates to classification or which publications have cited a sequence. I mean, GenBank would manage those data if they had them, but we submitters to GenBank don’t typically make the effort to keep them informed. Campbell & Lydeard (2026) recently estimated that 18.31% of COI sequences on GenBank are annotated with out-of-date taxonomy. If GenBank is the repository for these data, but the taxonomy isn’t being updated, how is anyone supposed to know what they are really dealing with?
Now is when we get to a solution: the MUSSEL Project Database! Yep, this essay is a crummy commercial. The MUSSELpdb includes freshwater mussel GenBank accessions, and those are linked not only with their original publication, but also subsequent literature references that might include taxonomic revisions. The MUSSELpdb interface can facilitate locating and verifying the GenBank sequences you are seeking.
You can easily browse the available GenBank accessions for any freshwater mussel species starting at its Valid Genus page — e.g., Pseudodon for Mussel of the Month Pseudodon mekongi. Valid species are listed alphabetically, and for each, two paths to useful nucleotides are provided, as shown in the figure below.
The assortment of available GenBank sequences is reported for each species. For Mussel of the Month Pseudodon mekongi, there are several useful genes listed, including 16S, 28S, COI, and even mitochondrial genomes. Following those links will lead to the set of up to 200 most-cited GenBank accessions for each gene, sorted by their popularity. For each accession, its unique key (with a link to its associated MUSSELpdb data), original identification, known voucher specimen (with any other genes attributed to the same specimen), and a direct link to the nucleotides at GenBank are provided. In the page header, there is also a link to GenBank for the whole set of displayed accessions if you just want to grab them all. The COI accessions for Pseudodon mekongi Page from the MUSSELpdb will get you KP795029 and many more, with their associated data, like re-identifications and voucher specimens.
Another way to browse for nucleotide sequences for freshwater mussels is to explore the GenBank voucher specimens listed for each species on its Specimens page from the MUSSELpdb. For example, the Pseudodon mekongi Specimens Page lists the voucher specimens with associated GenBank accessions at the bottom. For some species, e.g. Pseudodon vondembuschianus, that may mean scrolling past lots of other specimen records to get to the GenBank vouchers.
The MUSSEL Project Database Search Engine — the MUSSELpdb-se — also provides quick access to the current identifications of GenBank accessions. Up to 10 space-delimited accession numbers can be searched at a time, and the result for each sequence reports the gene and the original identification, along with links to the GenBank Accession Page and the Valid Species Page for the current identification.
The MUSSEL Project Database Search engine was described, demonstrated, and discussed in a recent episode of The Whoo! on the MUSSELp YouTube channel.
The upshot here is that the MUSSELpdb integrates current freshwater mussel taxonomy, GenBank accessions, specimen collections, and the published literature. Hopefully, it is easier than ever for researchers to make meaningful contributions to freshwater mussel systematics. I hope clicking around the resources described above offers some phylogenetic inspiration.
Feel free to leave a comment on this post about other useful database queries that could be accommodated by the MUSSEL Project Database Search Engine.
References Cited
Campbell, D.C. & C. Lydeard. 2026. Three decades of mussel mitochondria. Malacologia 68(1/2): 237-294.
Pfeiffer, J.M. & D.L. Graf. 2015. Evolution of bilaterally asymmetrical larvae in freshwater mussels (Bivalvia: Unionoida: Unionidae). Zoological Journal of the Linnean Society 175(2): 307-318.
Zieritz, A., G.R. Sumaedi, M. Lopes-Lima, A.A. Rofiqoh, T. Richmond et al. 2026. The freshwater mussels (Bivalvia: Unionida) of Java: first island-wide assessment reveals new species, endemism, and urgent conservation needs. Journal of the Linnean Society, Zoology 206(2), zlaf198: 1-18.