Most species in this genus have 14 leg pairs, and O. nanus has only 13 pairs,[5][6][7] the minimum number found in the phylum Onychophora.[8] Velvet worms in this genus are also among the smallest known, with adults often only 10 to 20 mm long. Species in this genus range in size from O nanus, which can be only 5 mm long, to O. nickmayeri, which can reach 60 mm in length.[7] Velvet worms in this genus have no modified head papillae, the males feature a cruciform genital opening (gonopore), and the females feature an ovipositor.[4][7] This genus contains all oviparous velvet worm species with 13 or 14 leg pairs and no modified head structures (e.g., sclerotized head organs).[7]
Phylogeny
In spite of a disjoint geographic distribution across New Zealand, Tasmania, and Southern Australia, morphological and molecular data indicate that this genus is a monophyletic group. Molecular studies indicate that this clade includes two subclades, one containing species in New Zealand and the other containing species in both Tasmania and mainland Australia. Paleogeographic evidence indicates that glacial events severed the land connection between Tasmania and mainland Australia more recently than rifting broke the land connection between Australia and New Zealand, which would explain the phylogenetic tree that emerges from molecular studies of this genus.[7]
Species
The genus contains the following species:[1][9][10]
^Ruhberg, Hilke (1985). Die Peripatopsidae (Onychophora): Systematik, Ökologie, Chorologie und phylogenetische Aspekte. Zoologica (in German). Stuttgart: Schweizerbart. pp. 126–127. ISBN978-3-510-55023-4.
