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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: Gastrotricha (hairy-bellied worms) is a phylum of microscopic aquatic invertebrates whose traditional morphology-based classification has been challenged in recent years. We report a new genus and species found using an integrative morphological and molecular approach, which is unrelated to morphologically similar species in the genera Aspidiophorus and Heterolepidoderma. The mitochondrial genome of the new taxon has the same number of genes and gene order as the only other gastrotrich mitogenome available, suggesting the conservation of mitochondria at the family level. (Image credit: M. Antonio Todaro.) [ABSTRACT FROM AUTHOR]

Bacterial strains affiliated to the phylogenetically shallow subcluster C (PnecC) of the 28 Polynucleobacter cluster, which is characterized by a minimal 16S rRNA gene sequence similarity of approx. 98.5 percent, have been reported to occur as obligate endosymbionts of 30 ciliates (Euplotes spp.), as well as to occur as free-living cells in the pelagic zone of freshwater habitats. We investigated if these two groups of closely related bacteria represent 32 strains fundamentally differing in lifestyle, or if they simply represent different stages of a facultative endosymbiotic lifestyle. The phylogenetic analysis of 16S rRNA gene and 16S34 23S ITS sequences of five endosymbiont strains from two different Euplotes species and 40 pure culture strains demonstrated host-species-specific clustering of the endosymbiont 36 sequences within the PnecC subcluster. The sequences of the endosymbionts showed characteristics indicating an obligate endosymbiotic lifestyle. Cultivation experiments 38 revealed fundamental differences in physiological adaptations, and determination of the genome sizes indicated a slight size reduction in endosymbiotic strains. We conclude that the 40 two groups of PnecC bacteria represent obligately free-living and obligately endosymbiotic strains, respectively, and do not represent different stages of the same complex lifecycle. 42 These closely related strains occupy completely separated ecological niches. To our best knowledge, this is the closest phylogenetic relationship between obligate endosymbionts and 44 obligately free-living bacteria ever revealed.

The history of the genus Copemetopus is tortuous and studded with several misattributions. It was erected by Villeneuve-Brachon in 1940 after the discovery of Copemetopus subsalsus in saline ponds along the French coast of the Mediterranean Sea near Sète and associated with the class Heterotrichea in the family Metopidae, close to Bryometopus. After a long series of systematic revisions, it is now clear that Copemetopus is not a heterotrich and that it falls in the subphylum Intramacronucleata. Nevertheless, a lot more work is needed to fix the complex taxonomic status of the genus, which lacks a precise taxonomic collocation (it is presently referred to as incertae sedis). In the present study focused on a multidisciplinary and detailed description of a new species, of the genus, Copemetopus mystakophoros sp. nov. , we also propose the erection of the new class, Copemetopea cl. nov. After careful literature and data revision, we believe that members of Copemetopus require a higher-ranked taxon in the phylum Ciliophora, given their molecular and morphological peculiarities. [ABSTRACT FROM AUTHOR]

The white-clawed crayfish is a complex of species (Austropotamobius pallipes plus A. italicus, Crustacea) pivotal to riverine environments. Regrettably, it is endangered in many European countries due to a recent massive decline. We carried out a fine-scale survey on white-clawed crayfish distribution, morphology and genetics in an under-investigated region of central Italy (Lunigiana, Tuscany) to improve local knowledge and aid conservation management of the species. The torrential fauna of Lunigiana is scarcely known and habitat alterations due to the anthropic exploitation of the territory represent a potential threat to its persistence. We investigated crayfish occurrence in eight streams of the Magra River Basin. We performed nocturnal and diurnal transects, took morphometric measurements, collected samples for genetic analysis and checked for the occurrence of ectosymbionts. Crayfish were disclosed in two streams (Civasola, Verdesina). Morphometric and phylogenetic analysis (mtDNA COI gene Bayesian tree reconstruction) concurrently identified both populations as Austropotamobius italicus carinthiacus. In the Verdesina stream, crayfish were heavily infested by branchiobdellidans (Annelida). Verdesina crayfish were also significantly smaller than those found in the Civasola stream, where branchiobdellidans were absent. Hence, we hypothesized that such difference in size might be related to the high density of ectosymbionts. In the light of habitat features and of data herein provided, we propose that both Civasola and Verdesina streams should be considered as “natural ark sites” for A. italicus, with the Magra River Basin representing a regional stronghold for the conservation of the species.