Chaetonotidae is the most diversified family of the entire phylum Gastrotricha; it comprises ~430 species distributed across 16 genera. The current classification, established mainly on morphological traits, has been challenged in recent years by phylogenetic studies, indicating that the cuticular ornamentations used to discriminate among species may be misleading when used to identify groupings, which has been the practice until now. Therefore, a consensus is developing toward implementing novel approaches to better define species identity and affiliation at a higher taxonomic ranking. Using an integrative morphological and molecular approach, including annotation of the mitogenome, we report on some freshwater gastrotrichs characterised by a mixture of two types of cuticular scales diagnostic of the genera Aspidiophorus and Heterolepidoderma. Our specimens’ overall anatomical characteristics find no correspondence in the taxa of these two genera, calling for their affiliation to a new species. Phylogenetic analyses based on the sequence of the ribosomal RNA genes of 96 taxa consistently found the new species unrelated to Aspidiophorus or Heterolepidoderma but allied with Chaetonotus aff. subtilis, as a subset of a larger clade, including mostly planktonic species. Morphological uniqueness and position along the non-monophyletic Chaetonotidae branch advocate erecting a new genus to accommodate the current specimens; consequently, the name Litigonotus ghinii gen. nov., sp. nov. is proposed. The complete mitochondrial genome of the new taxon resulted in a single circular molecule 14,384 bp long, including 13 protein-coding genes, 17 tRNA genes and 2 rRNAs genes, showing a perfect synteny and collinearity with the only other gastrotrich mitogenome available, a possible hint of a high level of conservation in the mitochondria of Chaetonotidae.

ZooBank: urn:lsid:zoobank.org:pub:9803F659-306F-4EC3-A73B-8C704069F24A

Accurate identification and precise classification of freshwater mussel species that are among the most threatened freshwater taxa in the world, play a crucial role in informing conservation and management efforts for these organisms. However, due to the variability in shell morphology, relying solely on shell characteristics for species taxonomy poses significant challenges, thereby impeding effective conservation planning and management. The freshwater mussel genus Ptychorhynchus Simpson, 1900 is one such group in need of study. We integrate molecular phylogeny, shell morphology and soft-body anatomy to examine the classification of Ptychorhynchus denserugata (Haas, 1910) and Ptychorhynchus resupinatus (von Martens, 1902). The COI barcoding data support the clustering of P. denserugata and Nodularia douglasiae within a single clade, and P. denserugata shares the diagnostic feature of the genus Nodularia, i.e. knobs or bumps on the inner mantle surface in the excurrent aperture. Therefore, by integrating molecular data and anatomical characteristics, we confirm that the nominal species P. denserugata syn. nov. is a new synonym for N. douglasiae. The multi-locus (COI + ND1 + 16S rRNA + 18S rRNA + 28S rRNA) phylogeny and mitochondrial phylogenomics support the transfer of P. resupinatus from Ptychorhynchus to the newly elevated genus Cosmopseudodon stat. rev., as Cosmopseudodon resupinatus stat. rev. that is still considered the designated type species. We also describe a new species based on integrative taxonomy, i.e. Cosmopseudodon wenshanensis sp. nov. The comprehensive understanding of the taxonomy and diversity of the revised Cosmopseudodon species, and shell heteromorphism of N. douglasiae (=P. denserugata syn. nov.), will serve as a crucial foundation for further scientific assessment and conservation strategies pertaining to these taxa.

ZooBank: urn:lsid:zoobank.org:pub:E48968B1-DF0F-42AD-8F31-B8C95F23CE57