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.

The taxonomy of the New World Peripatidae is poorly known both because of their rarity and difficulty in the determination of specimens. The distribution of papillae on the dorsal integument is an important taxonomic; character but is difficult to interpret under the light microscope. In this study the integument of a range of New World onychophoran species was studied using scanning electron microscopy. Twenty‐one species were examined. Three species of Peripatopsidae were also studied for comparison. This technique revealed (a) the pattern of distribution of papillae on the integument, and (b) the morphology of the papillae. A pattern of three smaller papillae between two large was common to many species. Differences observed in some species were probably modifications of this basic pattern. There was interspecific variation in the number of scales in the apical and basal pieces of the papillae. The specimens examined fell into two main groups: (1) species with more than three scale ranks in the apical piece (Oroperipatus and Peripatus) and (2) species with three or fewer scale ranks (Epiperipatus, Macroperipatus and others). The results thus support a distinction between Epiperipatus and Peripatus. However Macroperipatus is shown not to be a natural group. The relationships of some species which did not fit into this pattern are discussed. This paper shows scanning electron microscopy to be a potentially useful technique in a revision of the New World Peripatidae.

Macroperipatus torquatus feeds nocturnally on crickets and a few other invertebrates on the floor of the Trinidadian rain forest. Prey are inspected by gentle application of the antennae and, if suitable, are captured by entangling them in proteinaceous glue squirted from the oral papillae. Entangled prey are bitten through an arthrodial membrane and immobilized by injected saliva, which may also partly digest the flesh. Ingestion of the flesh takes several hours, comprising some 90% of total handling time, and normally only one prey item is eaten per night. The deplected carcass is discarded. Fully charged glue reserves amount to about 11% of body mass and after exhaustion are replenished in about 24 days. The quantity of glue used in an attack increases up to about 80% of reserve capacity for larger prey. Glue adhering to the prey is ingested, but some attached to the substratum is always lost. Squirting glue may therefore be costly for two reasons. Firstly, depleted glue reserves render peripatus less capable of attacking further prey or of defending themselves; secondly, unrecovered glue together with the metabolic cost of glue secretion will detract from the energetic yield of the prey. Small prey will scarcely repay the cost of glue used whereas larger ones are more likely to escape; consequently the energetically optimal prey are relatively large, but somewhat smaller than those potentially available. Accordingly, adult peripatus preferred larger prey and grew better when fed on them in the laboratory, whereas juveniles grew better on smaller prey. The size distribution of prey in the forest was heavily biased towards smaller types and it seemed likely that the productivity of large peripatus would be limited by the availability of profitable prey.