Phylogenetic and functional characterization of water bears (Tardigrada) tubulins.

Tardigrades are microscopic ecdysozoans that can withstand extreme environmental conditions. Several tardigrade species undergo reversible morphological transformations and enter into cryptobiosis, which helps them to survive periods of unfavorable environmental conditions. However, the underlying molecular mechanisms of cryptobiosis are mostly unknown. Tubulins are evolutionarily conserved components of the microtubule cytoskeleton that are crucial in many cellular processes. We hypothesize that microtubules are necessary for the morphological changes associated with successful cryptobiosis. The molecular composition of the microtubule cytoskeleton in tardigrades is unknown. Therefore, we analyzed and characterized tardigrade tubulins and identified 79 tardigrade tubulin sequences in eight taxa. We found three α-, seven ß-, one γ-, and one ε-tubulin isoform. To verify in silico identified tardigrade tubulins, we also isolated and sequenced nine out of ten predicted Hypsibius exemplaris tubulins. All tardigrade tubulins were localized as expected when overexpressed in mammalian cultured cells: to the microtubules or to the centrosomes. The presence of a functional ε-tubulin, clearly localized to centrioles, is attractive from a phylogenetic point of view. Although the phylogenetically close Nematoda lost their δ- and ε-tubulins, some groups of Arthropoda still possess them. Thus, our data support the current placement of tardigrades into the Panarthropoda clade.

Reproduction of Mesobiotus: Comparison of Morphology and Behavior in the Family Macrobiotidae (Tardigrada: Eutardigrada).

The genus Mesobiotus was separated from the genus Macrobiotus in 2016 and the name referred to its phylogenetic position among the family Macrobiotidae; however, knowledge of the reproductive behavior of this genus is limited compared to those of Paramacrobiotus and Macrobiotus. This study comprehensively provides the reproductive traits, including the gamete morphologies and behavioral observations, of Mesobiotus. The morphology of its spermatozoon showed a length that was intermediary among those of Paramacrobiotus and Macrobiotus species. The sequence of mating behavior was generally conserved in the three species of Macrobiotidae. They showed the described five steps observed in Paramacrobiotus and Macrobiotus; however, the males of Mesobiotus repeated ejaculations in a mating session, which is the first observation of premature ejaculation in tardigrades. Our results indicated that Mesobiotus has the potential to be a model to show the linkage between genera with respect to the morphology and behavior in the family Macrobiotidae.

Additional recommended abbreviations for the names of genera of the phylum Tardigrada.

Since we proposed the standardization of a three-letter abbreviation for the genera of the phylum Tardigrada (Perry et al. 2019) there have been 17 new genera and sub-genera described. In addition, we have been informed by colleagues using the three-letter abbreviations that some editors and reviewers have challenged the abbreviations as not meeting ICZN rules.

A new Tardigrade species, Stygarctus keralensis sp. nov. (Arthrotardigrada: Stygarctidae) from the intertidal zone of Southwest coast of India.

Stygarctus keralensis sp. nov. (Arthrotardigrada: Stygarctidae), is described from the intertidal sandy sediments of Vadakara beach, Kerala, Southwest coast of India. To a certain extent, this new species shows morphological similarity with Stygarctus gourbaultae Renaud-Mornant, 1981, however it can be differentiated by some significant distinguishable characters like double looped seminal receptacle ducts and the presence of a bow shaped internal thickening in between the opening of seminal receptacles situated below the level of gonopore and above the anus; unsculptured body plates I-III; paired sub-cephalic pore/muscle attachment; shape and structure of caudal processes. Presence of minute spikes on third lateral processes in the new species is another unique character by which it can be easily differentiated from S. gourbaultae.

An updated species list for "Smoky Bears": Tardigrades of the Great Smoky Mountains National Park, USA.

One of the largest inventories of tardigrades ever conducted occurred from 20002010 in the Great Smoky Mountains National Park, USA. Over 16,000 specimens were catalogued, 85 species were identified, 11 species new to science were described, and 16 other possible new species await further study. More than 20 papers have resulted from the GSMNP tardigrade inventory, making the Smokies the most thoroughly studied area in North America for tardigrades. Several species lists have been published over this 20-year period, but many taxonomic revisions and new identifications have led to significant changes to the list. Biogeographical studies citing species records from earlier studies could yield serious errors. Here we update the species list from the Smokies to accommodate the many recent changes in tardigrade taxonomy, we re-analyze some species in light of delineations of cryptic species groups that have occurred recently via integrative taxonomy, and we provide a table of all synonyms that have been used in previous publications. We also make available, for the first time, the Smokies tardigrade database, complete with all locations, elevations, and substrates.

20 years of Zootaxa: Tardigrada (Ecdysozoa: Panarthropoda).

Over the last two decades, Zootaxa has hosted nearly 200 papers concerning tardigrade taxonomy, systematics, phylogeny, and evolution. A total of 160 researchers from all continents (except the Antarctic) published descriptions of almost 200 new taxa, mostly species, but also genera and higher taxonomic ranks, such as families and superfamilies. This editorial is dedicated to the late Professor Clark W. Beasley who was the first tardigrade Associate Editor for Zootaxa.

Phylogeography and morphological evolution of Pseudechiniscus (Heterotardigrada: Echiniscidae).

Tardigrades constitute a micrometazoan phylum usually considered as taxonomically challenging and therefore difficult for biogeographic analyses. The genus Pseudechiniscus, the second most speciose member of the family Echiniscidae, is commonly regarded as a particularly difficult taxon for studying due to its rarity and homogenous sculpturing of the dorsal plates. Recently, wide geographic ranges for some representatives of this genus and a new hypothesis on the subgeneric classification have been suggested. In order to test these hypotheses, we sequenced 65 Pseudechiniscus populations extracted from samples collected in 19 countries distributed on 5 continents, representing the Neotropical, Afrotropical, Holarctic, and Oriental realms. The deep subdivision of the genus into the cosmopolitan suillus-facettalis clade and the mostly tropical-Gondwanan novaezeelandiae clade is demonstrated. Meridioniscus subgen. nov. is erected to accommodate the species belonging to the novaezeelandiae lineage characterised by dactyloid cephalic papillae that are typical for the great majority of echiniscids (in contrast to pseudohemispherical papillae in the suillus-facettalis clade, corresponding to the subgenus Pseudechiniscus). Moreover, the evolution of morphological traits (striae between dorsal pillars, projections on the pseudosegmental plate IV', ventral sculpturing pattern) crucial in the Pseudechiniscus taxonomy is reconstructed. Furthermore, broad distributions are emphasised as characteristic of some taxa. Finally, the Malay Archipelago and Indochina are argued to be the place of origin and extensive radiation of Pseudechiniscus.

An integrative description of Diploechiniscus oihonnae/ (Richters, 1903) population from near the original type locality in Merok (Norway).

In the present study, we used integrative taxonomy to describe a population of Diploechiniscus oihonnae (Richters, 1903) from the neotype locality in Merok (Norway). We found no differences in the chaetotaxy formula between the life stages and sex of Dpl. oihonnae. The presence of filaments at Bd in some specimens of Dpl. oihonnae appears to be random and most likely represents the morphological variability of this species. We also obtained DNA sequences of 18S rRNA, 28S rRNA, ITS-2, and COI of Dpl. oihonnae from the neotype locality for comparison with the sequences available in GenBank, which showed low genetic differences between the neotypic population and specimens from other localities. Therefore, we decided to establish our specimens from Merok as neotype and neoparatypes of Dpl. oihonnae. Additionally, based on morphological characters, Dpl. horningi (Schuster Grigarick, 1971) was synonymised with Dpl. oihonnae.

New multilocus phylogeny reorganises the family Macrobiotidae (Eutardigrada) and unveils complex morphological evolution of the Macrobiotus hufelandi group.

The family Macrobiotidae is one of the most speciose and diverse groups among tardigrades. Although there have been attempts to reconstruct the phylogeny of this family, the evolutionary relationships within Macrobiotidae are only superficially determined as available genetic data cover only a small fraction of this vast group. Here, we present the first extensive molecular phylogeny of the family based on four molecular markers (18S rRNA, 28Sr RNA, ITS-2 and COI) associated with detailed morphological data for the majority of taxa. The phylogenetic analysis includes nearly two hundred sequences representing more than sixty species, including sixteen taxa that have never been sequenced and/or analysed phylogenetically before. Our results recovered a new monophyletic group, comprising Macrobiotus spectabilis Thulin, 1928 and Macrobiotus grandis Richters, 1911, for which we erect a new genus, Sisubiotusgen. nov., to accommodate its evolutionary distinctiveness. The largest, so far, dataset for the family Macrobiotidae showed that the genus Xerobiotus is nested within the clade representing the genus Macrobiotus deeper than it was earlier assumed, therefore we propose to suppress Xerobiotus and transfer its species to Macrobiotus. Moreover, mapping key morphological traits onto macrobiotid phylogeny exposed complex evolution of phenotypes within the Macrobiotus hufelandi group, i.e. Macrobiotus s.s. Finally, our findings enabled a detailed revision and discussion on species compositions of the most ubiquitous tardigrade genera, species groups and species complexes, which resulted in changes of taxonomic statuses of a number of macrobiotid species. All this contributes to the reconstruction of the morphological evolution within Macrobiotidae.

Multi-marker DNA metabarcoding reflects tardigrade diversity in different habitats.

Like meiofauna in general, tardigrades are often neglected in ecological and environmental surveys. Tardigrades occur in all parts of the world, from deep marine sediments to alpine environments, and are present in most ecosystems. They are therefore potentially good candidates for biomonitoring programs. However, sampling of these minute animals is both tedious and time-consuming, impeding their inclusion in large-scale ecological surveys. In this study we argue that using a multi-marker metabarcoding approach on environmental DNA (eDNA) partly can overcome this barrier. Samples of moss, lichens, and leaf litter were investigated both by morphology-based methods and DNA metabarcoding, and the results were compared in terms of tardigrade diversity and community composition of the sampled microhabitats. DNA metabarcoding using three markers detected more species of tardigrades than identification by morphology in most samples. Also, metabarcoding detected the same community differences and microhabitat distribution patterns as morphology-based methods. In general, metabarcoding of litter samples was unreliable, with only one out of three markers consistently amplifying and detecting tardigrades. The low availability of tardigrade reference sequences in public databases restricts the taxonomic resolution in eDNA surveys, but this impediment is partly circumvented by utilizing multiple markers.

Resolving the systematics of Richtersiidae by multilocus phylogeny and an integrative redescription of the nominal species for the genus Crenubiotus (Tardigrada).

The family Richtersiidae, although established recently with the use of phylogenetic methods, was considered potentially paraphyletic at the time of its erection. Until now, the family comprised four genera, Richtersius, Diaforobiotus, Adorybiotus and a newly erected genus Crenubiotus. However, the genetic characterisation for the latter two genera was very limited or absent. To address concerns about the phylogenetic affinity of these two genera, we present a multilocus phylogeny of the families Richtersiidae and Murrayidae based on four molecular markers (18S rRNA, 28S rRNA, ITS-2 and COI). Our results show a distinct evolutionary lineage composed of Adorybiotus and Crenubiotus, which is sister to Murrayidae. In order to accommodate the phylogenetic and morphological distinctiveness of this lineage, we erect a new family, Adorybiotidae fam. nov. The new taxon differs morphologically from other families in the superfamily Macrobiotoidea by a unique combination of traits: (1) the presence of tubercles/cushions with aggregations of microgranules on their surfaces present on all legs and on the dorso-caudal cuticle, (2) a system of internal septa in claws, and (3) buccal apparatus morphology. Moreover, in order to stabilise the taxonomy and nomenclature in the genus Crenubiotus, we redescribe its type species, Crenubiotus crenulatus, by means of integrative taxonomy and designate a new neotype based on a population from the original terra typica.

Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan.

BACKGROUND: Ecdysozoa are the moulting protostomes, including arthropods, tardigrades, and nematodes. Both the molecular and fossil records indicate that Ecdysozoa is an ancient group originating in the terminal Proterozoic, and exceptional fossil biotas show their dominance and diversity at the beginning of the Phanerozoic. However, the nature of the ecdysozoan common ancestor has been difficult to ascertain due to the extreme morphological diversity of extant Ecdysozoa, and the lack of early diverging taxa in ancient fossil biotas. RESULTS: Here we re-describe Acosmia maotiania from the early Cambrian Chengjiang Biota of Yunnan Province, China and assign it to stem group Ecdysozoa. Acosmia features a two-part body, with an anterior proboscis bearing a terminal mouth and muscular pharynx, and a posterior annulated trunk with a through gut. Morphological phylogenetic analyses of the protostomes using parsimony, maximum likelihood and Bayesian inference, with coding informed by published experimental decay studies, each placed Acosmia as sister taxon to Cycloneuralia + Panarthropoda-i.e. stem group Ecdysozoa. Ancestral state probabilities were calculated for key ecdysozoan nodes, in order to test characters inferred from fossils to be ancestral for Ecdysozoa. Results support an ancestor of crown group ecdysozoans sharing an annulated vermiform body with a terminal mouth like Acosmia, but also possessing the pharyngeal armature and circumoral structures characteristic of Cambrian cycloneuralians and lobopodians. CONCLUSIONS: Acosmia is the first taxon placed in the ecdysozoan stem group and provides a constraint to test hypotheses on the early evolution of Ecdysozoa. Our study suggests acquisition of pharyngeal armature, and therefore a change in feeding strategy (e.g. predation), may have characterised the origin and radiation of crown group ecdysozoans from Acosmia-like ancestors.

Milnesium (Tardigrada: Apochela) in Japan: The First Confirmed Record of Milnesium tardigradum s.s. and Description of Milnesium pacificum sp. nov.

Presently, more than 40 species of the genus Milnesium Doyère, 1840 (Tardigrada: Eutardigrada: Apochela: Milnesiidae) have been described. In Japan, however, almost all records of milnesiid tardigrades should be re-examined with the current criteria on the taxonomy of this genus, except for one species, the recently described Milnesium inceptum Morek, Suzuki, Schill, Georgiev, Yankova, Marley, and Michalczyk, 2019. In this study, we found two species, Milnesium pacificum sp. nov. and Milnesium tardigradum Doyère, 1840, from three southern islands and two cold regions in Japan, respectively. Milnesium pacificum sp. nov., having dorsal sculpturing, exhibits an early positive change in claw configuration. On the other hand, M. tardigradum s.s. from Japan has an early negative claw configuration change, as has been reported in a recent study on the neotype population of this species. We performed DNA barcoding for both species, which indicated that M. pacificum sp. nov. has a close affinity with an undescribed Milnesium species collected from Brazil, and that M. tardigradum from Japan represents the recently described subclade that contains specimens from Poland, Hungary, and Russia. The chromosome numbers were 2n = 14 in M. pacificum sp. nov. and 2n = 10 in M. tardigradum. We detected at least three species of the genus Milnesium present in Japan. Our results advance the investigation of the relationship between phylogenetic position and characteristic morphology as well as expand the known geographic range of M. tardigradum.

Integrative description of bisexual Paramacrobiotus experimentalis sp. nov. (Macrobiotidae) from republic of Madagascar (Africa) with microbiome analysis.

In a moss samples collected on Madagascar two populations of Paramacrobiotus experimentalis sp. nov. were found. Paramacrobiotus experimentalis sp. nov. with the presence of a microplacoid and areolatus type of eggs is similar to Pam. danielae, Pam. garynahi, Pam. hapukuensis, Pam. peteri, Pam. rioplatensis and Pam. savai, but it differs from them by some morphological and morphometric characters of the eggs. The p-distance between two COI haplotypes of Pam. experimentalis sp. nov. was 0.17%. In turn, the ranges of uncorrected genetic p-distances of all Paramacrobiotus species available in GenBank was from 18.27% (for Pam. lachowskae) to 25.26% (for Pam. arduus) with an average distance of 20.67%. We also found that Pam. experimentalis sp. nov. is bisexual. This observation was congruent on three levels: (i) morphological - specimen size dimorphism; (ii) structural (primary sexual characteristics) - females have an unpaired ovary while males have an unpaired testis and (iii) molecular - heterozygous and homozygous strains of the ITS-2 marker. Although symbiotic associations of hosts with bacteria (including endosymbiotic bacteria) are common in nature and these interactions exert various effects on the evolution, biology and reproductive ecology of hosts, there is still very little information on the bacterial community associated with tardigrades. To fill this gap and characterise the bacterial community of Pam. experimentalis sp. nov. populations and microbiome of its microhabitat, high throughput sequencing of the V3-V4 hypervariable regions in the bacterial 16S rRNA gene fragment was performed. The obtained 16S rRNA gene sequences ranged from 92,665 to 131,163. In total, 135 operational taxonomic units (OTUs) were identified across the rarefied dataset. Overall, both Pam. experimentalis sp. nov. populations were dominated by OTUs ascribed to the phylum Proteobacteria (89-92%) and Firmicutes (6-7%). In the case of samples from tardigrades' laboratory habitat, the most abundant bacterial phylum was Proteobacteria (51-90%) and Bacteroides (9-48%). In all compared microbiome profiles, only 16 of 137 OTUs were shared. We found also significant differences in beta diversity between the partly species-specific microbiome of Pam. experimentalis sp. nov. and its culturing environment. Two OTUs belonging to a putative bacterial endosymbiont were identified - Rickettsiales and Polynucleobacter. We also demonstrated that each bacterial community was rich in genes involved in membrane transport, amino acid metabolism, and carbohydrate metabolism.

Comparative myoanatomy of Tardigrada: new insights from the heterotardigrades Actinarctus doryphorus (Tanarctidae) and Echiniscoides sigismundi (Echiniscoididae).

BACKGROUND: Tardigrada is a group of microscopic invertebrates distributed worldwide in permanent and temporal aquatic habitats. Famous for their extreme stress tolerance, tardigrades are also of interest due to their close relationship with Arthropoda and Cycloneuralia. Despite recent efforts in analyzing the musculature of a number of tardigrade species, data on the class Heterotardigrada remain scarce. Aiming to expand the current morphological framework, and to promote the use of muscular body plans in elucidating tardigrade phylogeny, the myoanatomy of two heterotardigrades, Actinarctus doryphorus and Echiniscoides sigismundi, was analyzed by cytochemistry, scanning electron and confocal laser scanning microscopy and 3D imaging. We discuss our findings with reference to other tardigrades and internal phylogenetic relationships of the phylum. RESULTS: We focus our analyses on the somatic musculature, which in tardigrades includes muscle groups spanning dorsal, ventral, and lateral body regions, with the legs being musculated by fibers belonging to all three groups. A pronounced reduction of the trunk musculature is seen in the dorsoventrally compressed A. doryphorus, a species that generally has fewer cuticle attachment sites as compared to E. sigismundi and members of the class Eutardigrada. Interestingly, F-actin positive signals were found in the head appendages of A. doryphorus. Our analyses further indicate that cross-striation is a feature common to the somatic muscles of heterotardigrades and that E. sigismundi-as previously proposed for other echiniscoidean heterotardigrades-has relatively thick somatic muscle fibers. CONCLUSIONS: We provide new insights into the myoanatomical differences that characterize distinct evolutionary lineages within Tardigrada, highlighting characters that potentially can be informative in future phylogenetic analyses. We focus our current analyses on the ventral trunk musculature. Our observations suggest that seven paired ventromedian attachment sites anchoring a large number of muscles can be regarded as part of the ground pattern of Tardigrada and that fusion and reduction of cuticular attachment sites is a derived condition. Specifically, the pattern of these sites differs in particular details between tardigrade taxa. In the future, a deeper understanding of the tardigrade myoanatomical ground pattern will require more investigations in order to include all major tardigrade lineages.

Reproduction, Gonad Structure, and Oogenesis in Tardigrades.

Even though tardigrades have been known since 1772, their phylogenetic position is still controversial. Tardigrades are regarded as either the sister group of arthropods, onychophorans, or onychophorans plus arthropods. Furthermore, the knowledge about their gametogenesis, especially oogenesis, is still poor and needs further analysis. The process of oogenesis has been studied solely for several eutardigradan species. Moreover, the spatial organization of the female germ-line clusters has been described for three species only. Meroistic ovaries characterize all analyzed species. In species of the Parachela, one cell per germ-cell cluster differentiates into the oocyte, while the remaining cells become the trophocytes. In Apochela several cells in the cluster differentiate into oocytes. Vitellogenesis is of a mixed type. The eggs are covered with the egg capsule that is composed of two shells: the thin vitelline envelope that adheres to the oolemma and the thick three-layered chorion. Chorion is formed as a first followed by vitelline envelope. Several features related to the oogenesis and structure of the ovary confirm the hypothesis that tardigrades are the sister group rather for arthropods than for onychophorans.

Comparative transcriptomics suggest unique molecular adaptations within tardigrade lineages.

BACKGROUND: Tardigrades are renowned for their ability to enter cryptobiosis (latent life) and endure extreme stress, including desiccation and freezing. Increased focus is on revealing molecular mechanisms underlying this tolerance. Here, we provide the first transcriptomes from the heterotardigrade Echiniscoides cf. sigismundi and the eutardigrade Richtersius cf. coronifer, and compare these with data from other tardigrades and six eukaryote models. Investigating 107 genes/gene families, our study provides a thorough analysis of tardigrade gene content with focus on stress tolerance. RESULTS: E. cf. sigismundi, a strong cryptobiont, apparently lacks expression of a number of stress related genes. Most conspicuous is the lack of transcripts from genes involved in classical Non-Homologous End Joining. Our analyses suggest that post-cryptobiotic survival in tardigrades could rely on high fidelity transcription-coupled DNA repair. Tardigrades seem to lack many peroxins, but they all have a comprehensive number of genes encoding proteins involved in antioxidant defense. The "tardigrade unique proteins" (CAHS, SAHS, MAHS, RvLEAM), seem to be missing in the heterotardigrade lineage, revealing that cryptobiosis in general cannot be attributed solely to these proteins. Our investigation further reveals a unique and highly expressed cold shock domain. We hypothesize that the cold shock protein acts as a RNA-chaperone involved in regulation of translation following freezing. CONCLUSIONS: Our results show common gene family contractions and expansions within stress related gene pathways in tardigrades, but also indicate that evolutionary lineages have a high degree of divergence. Different taxa and lineages may exhibit unique physiological adaptations towards stress conditions involving possible unknown functional homologues and/or novel physiological and biochemical mechanisms. To further substantiate the current results genome assemblies coupled with transcriptome data and experimental investigations are needed from tardigrades belonging to different evolutionary lineages.

Biotic interactions are an unexpected yet critical control on the complexity of an abiotically driven polar ecosystem.

Abiotic and biotic factors control ecosystem biodiversity, but their relative contributions remain unclear. The ultraoligotrophic ecosystem of the Antarctic Dry Valleys, a simple yet highly heterogeneous ecosystem, is a natural laboratory well-suited for resolving the abiotic and biotic controls of community structure. We undertook a multidisciplinary investigation to capture ecologically relevant biotic and abiotic attributes of more than 500 sites in the Dry Valleys, encompassing observed landscape heterogeneities across more than 200 km2. Using richness of autotrophic and heterotrophic taxa as a proxy for functional complexity, we linked measured variables in a parsimonious yet comprehensive structural equation model that explained significant variations in biological complexity and identified landscape-scale and fine-scale abiotic factors as the primary drivers of diversity. However, the inclusion of linkages among functional groups was essential for constructing the best-fitting model. Our findings support the notion that biotic interactions make crucial contributions even in an extremely simple ecosystem.

Nematodes in a polar desert reveal the relative role of biotic interactions in the coexistence of soil animals.

Abiotic factors are major determinants of soil animal distributions and their dominant role is pronounced in extreme ecosystems, with biotic interactions seemingly playing a minor role. We modelled co-occurrence and distribution of the three nematode species that dominate the soil food web of the McMurdo Dry Valleys (Antarctica). Abiotic factors, other biotic groups, and autocorrelation all contributed to structuring nematode species distributions. However, after removing their effects, we found that the presence of the most abundant nematode species greatly, and negatively, affected the probability of detecting one of the other two species. We observed similar patterns in relative abundances for two out of three pairs of species. Harsh abiotic conditions alone are insufficient to explain contemporary nematode distributions whereas the role of negative biotic interactions has been largely underestimated in soil. The future challenge is to understand how the effects of global change on biotic interactions will alter species coexistence.

A review of the Quaternary Scelidotheriinae (Mammalia, Xenarthra, Tardigrada) from the Tarija-Padcaya basin, Bolivia.

The Mylodontidae Scelidotheriinae (Mammalia, Xenarthra, Tardigrada) are a diversified clade of South American fossil ground sloths, with a wide geographic distribution, especially in high and middle latitudes. According to the last revision, the Quaternary diversity includes the genera Scelidotherium, Catonyx, and Valgipes. The clade Scelidotheriinae is well represented in the Pleistocene of the Tarija-Padcaya basin, and the first mention of these ground sloths correspond to the middle of the XIX Century. Since then, several species (i.e., Scelidotherium tarijensis, Scelidodon tarijensis, Scelidotherium capellini) have been reported as inhabiting the Tarija-Padcaya basin during the Pleistocene. Despite the abundance of fossil records of Scelidotheriinae in this area, no modern taxonomic revisions are available. In consequence, in this contribution a revision of the remains assigned to Scelidotheriinae from the Tarija-Padcaya basin is accomplished, and some biostratigraphic and geographic implications are discussed. Our results show that one single species (Catonyx tarijensis) can be recognized in the studied area, whereas a supposed smaller one (Scelidotherium patrium) actually corresponds to juvenile specimens of C. tarijensis.