We had a thread a few weeks back in which we were discussing the differences in the three "rummynose" tetras. A new study published electronically on June 26, 2020 in the journal Neotropical Ichthyology proposes the taxonomic revision of the three "rummynose" tetra species Hemigrammus rhodostomus Ahl, 1924, Hemigrammus bleheri Gery & Mahnert, 1986 and Petitella georgiae Gery & Boutiere, 1964. The study is "Phylogenetic relationships of the neon tetras Paracheirodon spp. (Characiformes: Characidae: Stethaprioninae), including comments on Petitella georgiae and Hemigrammus bleheri," and the authors are Pedro Senna Bittencourt, Valéria Nogueira Machado, Bruce Gavin Marshall, Tomas Hrbek and Izeni Pires Farias. The paper can be referenced in abbreviated form as Bittencourt et al, 2020. I will link the paper at the end.
H. rhodostomus was the first rummynose tetra to be discovered and described. In 1924, a young German researcher, Gustav Ernst Ahl (who in later life was the Director of the Natural History Museum in Berlin), discovered the fish in the tributaries of the Rio Orinoco in Venezuela, and subsequently described the species. The species epithet is from the Greek and translates as "rose's mouth."
The second species discovered three or four decades later was Petitella georgiae in the Purus and Madeira rivers which are located in the southern Amazon basin. Following years of study, Jacques Gery and Henry Boutiere described the distinct species in 1964. The species epithet georgiae honours Gery's wife, Georgie. Gery & Boutiere erected the new genus Petitella, and up to the present this has been the only species assigned to the genus.
Gery, who was during his life (he died in June 2007) the unequalled authority on the characidae, enters the story again. In the 1960's the then-20 year old explorer Heiko Bleher discovered the third "rummynose" in the middle Rio Negro. Gery & Mahnert (1984) described the species as Hemigrammus bleheri, in honour of its discoverer. Heiko in his 60+ years as an explorer has discovered more than 6000 new species of fish across the globe--including a fourth "neon tetra" which is awaiting description.
The occurrence of three distinct species which nevertheless bear such remarkable similarity to one another has long intrigued ichthyologists. The external characteristics of these species are unique among all known characidae. "The genus Petitella is readily distinguished from all remaining characid genera by the possession of a distinctively bright red head, the presence of a black horizontal bar that extends from the end of the caudal peduncle to the middle rays of the caudal-fin, and the presence of an oblique black bar in each caudal-fin lobe, separated by white colored bands" (Bittencourt et al, 2020).
The prime focus of this study was to "test the Paracheirodon monophyly hypothesis using a molecular phylogenetic approach, through analysis of the mitochondrial genes cytochrome C oxidase subunit I (COI) and the 16S ribosomal RNA (16S rRNA)." The three species Paracheirodon innesi, P. axelrodi and P. simulans form a monophyletic clade, meaning that the three distinct species descended from a common ancestor. Other species were involved in the analysis, leading us to the three rummynose tetras. The paper's abstract is a good summary:
Under the rules of the International Commission on Zoological Nomenclature (ICZN), publication of the paper revises the taxonomy. The genus Petitella Gery & Butiere, 1964 now holds three species; the type species Petitella georgiae Gery & Boutiere, 1964, and Petitella rhodostomus (Ahl, 1924) and Petitella bleheri (Gery & Mahnert, 1984). "Type species" is the species first described within the genus and all subsequent species in the genus will share the identical characteristics which cause them to be unique to this assemblage; note that this may include differing external markings which do not necessarily alter the distinct biological traits that the species in the genus must share. The describer's names when in brackets indicates that while they were the first to described the species as distinct, it has since been transferred to a different genus from the one in which it was initially described.
Edited July 7 to correct species epithet of P. rhodostomus.
H. rhodostomus was the first rummynose tetra to be discovered and described. In 1924, a young German researcher, Gustav Ernst Ahl (who in later life was the Director of the Natural History Museum in Berlin), discovered the fish in the tributaries of the Rio Orinoco in Venezuela, and subsequently described the species. The species epithet is from the Greek and translates as "rose's mouth."
The second species discovered three or four decades later was Petitella georgiae in the Purus and Madeira rivers which are located in the southern Amazon basin. Following years of study, Jacques Gery and Henry Boutiere described the distinct species in 1964. The species epithet georgiae honours Gery's wife, Georgie. Gery & Boutiere erected the new genus Petitella, and up to the present this has been the only species assigned to the genus.
Gery, who was during his life (he died in June 2007) the unequalled authority on the characidae, enters the story again. In the 1960's the then-20 year old explorer Heiko Bleher discovered the third "rummynose" in the middle Rio Negro. Gery & Mahnert (1984) described the species as Hemigrammus bleheri, in honour of its discoverer. Heiko in his 60+ years as an explorer has discovered more than 6000 new species of fish across the globe--including a fourth "neon tetra" which is awaiting description.
The occurrence of three distinct species which nevertheless bear such remarkable similarity to one another has long intrigued ichthyologists. The external characteristics of these species are unique among all known characidae. "The genus Petitella is readily distinguished from all remaining characid genera by the possession of a distinctively bright red head, the presence of a black horizontal bar that extends from the end of the caudal peduncle to the middle rays of the caudal-fin, and the presence of an oblique black bar in each caudal-fin lobe, separated by white colored bands" (Bittencourt et al, 2020).
The prime focus of this study was to "test the Paracheirodon monophyly hypothesis using a molecular phylogenetic approach, through analysis of the mitochondrial genes cytochrome C oxidase subunit I (COI) and the 16S ribosomal RNA (16S rRNA)." The three species Paracheirodon innesi, P. axelrodi and P. simulans form a monophyletic clade, meaning that the three distinct species descended from a common ancestor. Other species were involved in the analysis, leading us to the three rummynose tetras. The paper's abstract is a good summary:
Neon tetras (Paracheirodon spp.) are three colorful characid species with a complicated taxonomic history, and relationships among the species are poorly known. 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.
Under the rules of the International Commission on Zoological Nomenclature (ICZN), publication of the paper revises the taxonomy. The genus Petitella Gery & Butiere, 1964 now holds three species; the type species Petitella georgiae Gery & Boutiere, 1964, and Petitella rhodostomus (Ahl, 1924) and Petitella bleheri (Gery & Mahnert, 1984). "Type species" is the species first described within the genus and all subsequent species in the genus will share the identical characteristics which cause them to be unique to this assemblage; note that this may include differing external markings which do not necessarily alter the distinct biological traits that the species in the genus must share. The describer's names when in brackets indicates that while they were the first to described the species as distinct, it has since been transferred to a different genus from the one in which it was initially described.
Edited July 7 to correct species epithet of P. rhodostomus.
Last edited:
