A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe

Abstract

The subgenus Hystricochaetonotus Schwank, 1990 is one of the most species-rich subgenera of Chaetonotus Ehrenberg, 1830. It has a worldwide distribution and encompasses 37 species predominantly living in the benthos and periphyton of limnetic habitats. We have discovered further nine new species in running and stagnant waters in Slovakia (Central Europe): Ch. (H.) arcanus sp. nov., Ch. (H.) avarus sp. nov., Ch. (H.) gulosus sp. nov., Ch. (H.) iratus sp. nov., Ch. (H.) luxus sp. nov., Ch. (H.) mirabilis sp. nov., Ch. (H.) optabilis sp. nov., Ch. (H.) slavicus sp. nov., and Ch. (H.) superbus sp. nov. Their morphology was studied using differential interference contrast microscopy and subsequent morphometric analyses were carried out. In addition, the primary and secondary structures of their 18S, ITS2, and 28S rRNA molecules as well as their barcoding mitochondrial gene encoding for cytochrome c oxidase (COI) were analyzed. Species boundaries were tested also using the compensatory base change analysis. The new species could be well separated both morphologically and molecularly. The present barcoding analyses revealed that the nuclear ITS2 sequences represent a powerful DNA barcode in addition to the mitochondrial COI gene. According to the multi-gene phylogenetic analyses, the lineage leading to the last common ancestor of the ‘Hystricochaetonotus’ clade is the longest internal branch within the family Chaetonotidae Gosse, 1864. Since members of the subgenus Hystricochaetonotus are morphologically highly heterogeneous, parallel evolution of Chaetonotus-like and/or Hystricochaetonotus-like characters of scales and spines occurred during its radiation.

Freshwater and limno-terrestrial meiofauna of the Massane Forest Reserve in the Eastern French Pyrenees

“…However, according to the systematics presented on the GWP (Todaro & Tongiorgi 2023), Hystricochaetonotus is still considered a subgenus of genus Chaetonotus and Lepidochaetus still considered a genus rather than a subgenus. Furthermore, recent comprehensive molecular phylogenetic studies demonstrate the monophyly of Lepidochaetus, being quite separate from other species of Chaetonotus (Križanová & Vd'ačný 2021, Križanová & Vďačný 2022) and a monophyletic Hystricochaetonotus (Križanová & Vďačný 2022) each time with a maximum statistic node support. In the present publication we therefore follow the current taxonomy according to the GWP with, a subgenus status for Hystricochaetonotus and a genus status for Lepidochaetus.…”

“…Recently, further new species were described from freshwater biotopes in central Europe (e.g. Križanová & Vďačný 2021, Križanová & Vďačný 2022 and therefore there may be around 260 species recorded from this continent. Compared to this number, 47 species records for the whole of France most likely do not reflect the true diversity present.…”

Status of the Italian Freshwater Gastrotricha Biodiversity, with the Creation of an Interactive GIS-Based Web Map

“…It would also be interesting to screen out genetically disjunct populations of widely distributed species in order to confirm the status of these taxa or, conversely, establish whether they are reproductively isolated but morphologically indistinguishable populations, thus identifying phenomena of cryptic or pseudo-cryptic speciation [58].…”