The three species of rummynose, Hemigrammus bleheri, H.rhodostomus and Petitella georgiae have now all been placed into Petitella, in a paper published in the journal Neotropical Ichthyology. Pedro Bittencourt, Valeria Machado, Bruce Marshall, Tomas Hrbek and Izeni of the Universidade Federal do Amazonas published the paper on the phylogenetic relationships of Paracheirodon spp, but in it also examined rummynose tetras and moved all three species into Petitella. They found that Neons, Cardinals and Green neons should all stay together, and that they were closely related to the genus Brittanichthys, so the grouping of the Rummynose is actually the bigger finding.
“Neon tetras (Paracheirodon spp.) are three colorful characid species with a complicated taxonomic history, and relationships among the species are poorly known.” say the authors in the Abstract.
“Molecular data resolved the relationships among the three neon tetras, and strongly supported monophyly of the genus and its sister taxon relationship to Brittanichthys. Additionally, the sister-taxon relationship of the rummy-nose tetras Hemigrammus bleheri and Petitella georgiae was strongly supported by molecular and morphological data. Therefore, we propose to transfer the rummy-nose tetras H. bleheri and H. rhodostomus to the genus Petitella. Furthermore, Petitella georgiae is likely to be a species complex comprised of at least two species.
Petitella georgiae species complex
So the three rummynose all move to Petitella based on their similarities to each other, but what’s interesting is that Petitella may soon expand to include four or more rummynose species. Although a much rarer import than what is now P.bleheri, Petitella georgiae are available wild-caught so the possibility is that, depending on where they were captured, the fourth Petitella species may already be in the hobby.
This happened recently with wild-caught Trigonostigma heteromorpha (Harlequin rasboras,) when a fifth Harlequin was discovered and subsequently named H.truncata. One more thing to note is that Hemigrammus rhodostomus becomes Petitella rhodostoma, due to Petitella being feminine.
If you’re scientifically minded and want to know more, you can read the full article here. https://www.scielo.br/scielo.php?script=sci_arttext&pid=S1679-62252020000200213&lng=en&nrm=iso.
Image credit By Soulkeeper – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=23479504