The rapid squirt of a proteinaceous slime jet endows velvet worms (Onychophora) with a unique mechanism for defence from predators and for capturing prey by entangling them in a disordered web that immobilizes their target. However, to date, neither qualitative nor quantitative descriptions have been provided for this unique adaptation. Here we investigate the fast oscillatory motion of the oral papillae and the exiting liquid jet that oscillates with frequencies f~30–60 Hz. Using anatomical images, high-speed videography, theoretical analysis and a physical simulacrum, we show that this fast oscillatory motion is the result of an elastohydrodynamic instability driven by the interplay between the elasticity of oral papillae and the fast unsteady flow during squirting. Our results demonstrate how passive strategies can be cleverly harnessed by organisms, while suggesting future oscillating microfluidic devices, as well as novel ways for micro and nanofibre production using bioinspired strategies.
Onychophorans, or velvet worms, are cryptic but extremely charismatic terrestrial invertebrates that have often been the subject of interesting biogeographic debate. Despite great interest, a well resolved and complete phylogeny of the group and a reliable chronogram have been elusive due to their broad geographic distribution, paucity of samples, and challenging molecular composition. Here we present a molecular phylogenetic analysis of Onychophora that includes previously unsampled and undersampled lineages and we analyse the expanded dataset using a series of nested taxon sets designed to increase the amount of information available for particular subclades. These include a dataset with outgroups, one restricted to the ingroup taxa, and three others for Peripatopsidae, Peripatidae and Neopatida (= the Neotropical Peripatidae). To explore competing biogeographic scenarios we generate a new time tree for Onychophora using the few available reliable fossils as calibration points. Comparing our results to those of Cyphophthalmi, we reconsider the hypothesis that velvet worms reached Southeast Asia via Eurogondwana, and conclude that a more likely scenario is that they reached Southeast Asia by rafting on the Sibumasu terrane. Our phylogenetic results support the reciprocal monophyly of both families as well as an early division between East and West Gondwana, also in both families, each beginning to diversify between the Permian and the Jurassic. Peripatopsidae clearly supports paraphyly of South Africa with respect to southern South America (Chile) and a sister group relationship of the Southeast Asian/New Guinean Paraperipatus to the Australian/New Zealand taxa. The latter includes a clade that divides between Western Australia and Eastern Australia and two sister clades of trans-Tasman species (one oviparous and one viviparous). This pattern clearly shows that oviparity is secondarily derived in velvet worms. Peripatidae finds a sister group relationship between the Southeast Asian Eoperipatus and the West Gondwanan clade, which divides into the African Mesoperipatus and Neopatida. The latter shows a well supported split between the Pacific Oroperipatus (although it is unclear whether they form one or two clades) and a sister clade that includes the members of the genera Peripatus, Epiperipatus, Macroperipatus and representatives of the monotypic genera Cerradopatus, Plicatoperipatus and Principapillatus. However, Peripatus, Epiperipatus and Macroperipatus are not monophyletic, and all the species from the monotypic genera are related to geographically close species. The same goes for the type species of Macroperipatus (from Trinidad, and sister group to other Trinidad and Tobago species of Epiperipatus) and Epiperipatus (from French Guiana, and related to other Guyana shield species of Epiperipatus and Peripatus). Geographic structure within Neopatida is largely obscured by an unresolved backbone, but many well supported instances of generic non-monophyly challenge the current taxonomic framework, which has often relied on anatomical characters that are untested phylogenetically.
Onychophora, or velvet worms, are a key group for understanding ecdysozoan evolution. It comprises two families: Peripatopsidae, largely of Austral distribution, and Peripatidae, which is circumtropical. The interrelationships between the members of Peripatidae present many taxonomic issues exacerbated in the radiation of the Neotropical species or Neopatida. To understand the phylogeny of Neopatida, and to test the information of such morphological characters, we gathered novel molecular and morphological datasets focusing on Neotropical specimens. Our data were analysed using a combination of parsimony and maximum likelihood for the individual and combined molecular and morphological datasets. An analysis of morphology alone was inconclusive, supporting the notion that morphological characters used in peripatid taxonomy have little power to resolve phylogenetic relationships among higher taxa in Neopatida. However, the analyses of molecular or combined data show a split of the Neotropical species into two clades, which we use to reassign genera. Epiperipatus, as currently understood, is non-monophyletic, because it includes species of monotypic genera. To avoid paraphyly of Epiperipatus, the following new combinations are proposed: Epiperipatus bouvieri (Fuhrmann, 1913), Epiperipatus hitoyensis (Oliveira et al., 2012a), Epiperipatus solorzanoi (Morera-Brenes & Monge-Nájera, 2010) and Epiperipatus sucuriuensis (Oliveira et al., 2015).
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