An updated world checklist of velvet worms (Onychophora) with notes on nomenclature and status of names.

More than a decade has passed since the publication of the only world checklist available for Onychophora. During this period, numerous nomenclatural acts and taxonomic changes have been suggested within the group and a wealth of novel data has been published on many taxa. Herein, the up-to-date taxonomic scenario within Onychophora is presented, with appraisal of name status. This checklist covers both extant (Peripatidae and Peripatopsidae) and fossil taxa, and each species is accompanied by information on synonyms, type designation, holotype location, type locality, and language of original description. Additional remarks include nomenclatural inconsistencies, synonymizations, name misspellings, conflicting collecting event data, availability of taxonomically informative molecular data, etc. According to the data, 237 species are currently assigned to Onychophora: 140 of Peripatopsidae, 92 of Peripatidae, and five fossil species with unclear relationship to extant taxa. Since the previous checklist, 37 species have been added to Onychophora, representing an increase of 18.5% in the diversity described for the group. Yet, taxonomic descriptions seem slow-paced, with an average of 3.6 onychophoran species being described annually. From the taxonomic standpoint, 216 species are valid, although many of them require morphological revision and molecular characterization; 21 species exhibit major taxonomic ambiguities and have been regarded as nomina dubia. Recurrent taxonomic issues identified in the literature include inaccurate collecting event data, doubtful taxonomic assignment of molecular sequences, and non-observance of nomenclatural rules. These and other taxonomic aspects are addressed herein in the light of the directives established by the International Code of Zoological Nomenclature.

Functional morphology of a lobopod: case study of an onychophoran leg.

Segmental, paired locomotory appendages are a characteristic feature of Panarthropoda-a diversified clade of moulting animals that includes onychophorans (velvet worms), tardigrades (water bears) and arthropods. While arthropods acquired a sclerotized exoskeleton and articulated limbs, onychophorans and tardigrades possess a soft body and unjointed limbs called lobopods, which they inherited from Cambrian lobopodians. To date, the origin and ancestral structure of the lobopods and their transformation into the jointed appendages are all poorly understood. We therefore combined high-resolution computed tomography with high-speed camera recordings to characterize the functional anatomy of a trunk lobopod from the onychophoran Euperipatoides rowelli. Three-dimensional reconstruction of the complete set of muscles and muscle fibres as well as non-muscular structures revealed the spatial relationship and relative volumes of the muscular, excretory, circulatory and nervous systems within the leg. Locomotory movements of individual lobopods of E. rowelli proved far more diverse than previously thought and might be governed by a complex interplay of 15 muscles, including one promotor, one remotor, one levator, one retractor, two depressors, two rotators, one flexor and two constrictors as well as muscles for stabilization and haemolymph control. We discuss the implications of our findings for understanding the evolution of locomotion in panarthropods.

Evaluation of contrasting techniques for X-ray imaging of velvet worms (Onychophora).

Non-invasive imaging techniques like X-ray computed tomography have become very popular in zoology, as they allow for simultaneous imaging of the internal and external morphology of organisms. Nevertheless, the effect of different staining approaches required for this method on samples lacking mineralized tissues, such as soft-bodied invertebrates, remains understudied. Herein, we used synchrotron radiation-based X-ray micro-computed tomography to compare the effects of commonly used contrasting approaches on onychophorans - soft-bodied invertebrates important for studying animal evolution. Representatives of Euperipatoides rowelli were stained with osmium tetroxide (vapour or solution), ruthenium red, phosphotungstic acid, or iodine. Unstained specimens were imaged using both standard attenuation-based and differential phase-contrast setups to simulate analyses with museum material. Our comparative qualitative analyses of several tissue types demonstrate that osmium tetroxide provides the best overall tissue contrast in onychophorans, whereas the remaining staining agents rather favour the visualisation of specific tissues and/or structures. Quantitative analyses using signal-to-noise ratio measurements show that the level of image noise may vary according to the staining agent and scanning medium selected. Furthermore, box-and-whisker plots revealed substantial overlap in grey values among structures in all datasets, suggesting that a combination of semiautomatic and manual segmentation of structures is required for comprehensive 3D reconstructions of Onychophora, irrespective of the approach selected. Our results show that X-ray micro-computed tomography is a promising technique for studying onychophorans and, despite the benefits and disadvantages of different staining agents for specific tissues/structures, this method retrieves informative data that may eventually help address evolutionary questions long associated with Onychophora.

Earliest Onychophoran in Amber Reveals Gondwanan Migration Patterns.

The anomalous occurrence of supposedly Gondwanan taxa in Laurasian-derived regions remains an intriguing chapter of paleobiogeographical history. Representatives of Peripatidae, a major subgroup of velvet worms (Onychophora), show a disjointed distribution in the neotropics, tropical Africa, and Southeast Asia, the latter being the only landmass previously associated with Laurasia [1, 2]. The arrival of these animals in Southeast Asia is explained by two alternative, albeit not mutually exclusive, hypotheses: an early migration via Europe before continental drift (Eurogondwana hypothesis) or transportation via insular India during the Cretaceous and Paleogene ("out-of-India" hypothesis) [3-6]. The latter hypothesis is based on a single extant species of Peripatidae, Typhloperipatus williamsoni, in India. †Cretoperipatus burmiticus from Myanmar is the oldest fossil onychophoran found in amber [7], dating to sometime between the two proposed scenarios, and hence crucial for clarifying how Gondwanan lineages of these low-vagility animals reached Southeast Asia (see also Supplemental Information). Based on the anatomical reconstruction of †C. burmiticus using synchrotron radiation-based X-ray microtomography (SRµCT) and comparisons with extant taxa, we resolved this fossil species within Onychophora, particularly within Peripatidae, with T. williamsoni as its closest extant relative. This suggests that an early Eurogondwanan migration of peripatids was the most likely event, as Burmese amber is too old to be compatible with the out-of-India hypothesis. Moreover, peripatids probably colonized India only recently from Myanmar, refuting the putative Gondwanan relict status of Indian onychophorans. Finally, preservation artifacts identified in the novel amber material might have a major impact on studies of onychophoran stem and/or crown groups.

A world checklist of Onychophora (velvet worms), with notes on nomenclature and status of names.

Currently, the number of valid species of Onychophora is uncertain. To facilitate taxonomic work on this understudied animal group, we present an updated checklist for the two extant onychophoran subgroups, Peripatidae and Peripatopsidae, along with an assessment of the status of each species. According to our study, 82 species of Peripatidae and 115 species of Peripatopsidae have been described thus far. However, among these 197 species, 20 are nomina dubia due to major taxonomic inconsistencies. Apart from nomina dubia, many of the valid species also require revision, in particular representatives of Paraperipatus within the Peripatopsidae, and nearly all species of Peripatidae. In addition to extant representatives, the record of unambiguous fossils includes three species with uncertain relationship to the extant taxa. For all species, we provide a list of synonyms, information on types and type localities, as well as remarks on taxonomic and nomenclatural problems and misspellings. According to recent evidence of high endemism and cryptic speciation among the Peripatidae and Peripatopsidae, previous synonyms are revised. Putative mutations, subspecies and variations are either raised to the species status or synonymised with corresponding taxa. In our revised checklist, we follow the rules and recommendations of the International Code of Zoological Nomenclature to clarify previous inconsistencies.

Unexplored character diversity in onychophora (velvet worms): A comparative study of three peripatid species.

Low character variation among onychophoran species has been an obstacle for taxonomic and phylogenetic studies in the past, however we have identified a number of new and informative characters using morphological, molecular, and chromosomal techniques. Our analyses involved a detailed examination of Epiperipatus biolleyi from Costa Rica, Eoperipatus sp. from Thailand, and a new onychophoran species and genus from Costa Rica, Principapillatus hitoyensisgen. et sp. nov.. Scanning electron microscopy on embryos and specimens of varying age revealed novel morphological characters and character states, including the distribution of different receptor types along the antennae, the arrangement and form of papillae on the head, body and legs, the presence and shape of interpedal structures and fields of modified scales on the ventral body surface, the arrangement of lips around the mouth, the number, position and structure of crural tubercles and anal gland openings, and the presence and shape of embryonic foot projections. Karyotypic analyses revealed differences in the number and size of chromosomes among the species studied. The results of our phylogenetic analyses using mitochondrial COI and 12S rRNA gene sequences are in line with morphological and karyotype data. However, our data show a large number of unexplored, albeit informative, characters in the Peripatidae. We suggest that analysing these characters in additional species would help unravel species diversity and phylogeny in the Onychophora, and that inconsistencies among most diagnostic features used for the peripatid genera in the literature could be addressed by identifying a suite of characters common to all peripatids.