The velvet worms (Onychophora) are considered living fossils and are closely related to the Euarthropoda. Onychophora possess a tracheal system for respiratory function, but oxygen-transport proteins have been considered unnecessary. Here, we show that the hemolymph of the Epiperipatus sp. (Onychophora: Peripatidae) contains an arthropod-type hemocyanin, demonstrating that such protein exists outside the Euarthropoda. Thus, the evolution of oxygen carriers preceded the divergence of the Onychophora and Euarthropoda and was most likely linked to the evolution of an efficient circulatory system in a low-oxygen environment. The cDNA of the Epiperipatus hemocyanin subunit comprises 2,287 bp and encodes for a protein of 641 aa (73.6 kDa). Phylogenetic analyses of the arthropod hemocyanin sequences show that the Onychophora form a robust sister-group of the Euarthropoda, whereas the monophyly of the Tracheata is not supported.
The systematics of Peripatopsis moseleyi (Wood-Mason, 1879), a widely distributed South Africa velvet worm species, was examined to test the occurrence of cryptic lineages within this taxon. A total of 81 specimens of P. moseleyi were collected from 12 localities throughout its known distribution in the Eastern Cape and KwaZulu-Natal provinces of South Africa. All specimens were sequenced for a 631 bp fragment of the mitochondrial cytochrome oxidase one subunit (COI) locus, while a 717 bp pair fragment of the 18S rDNA locus was sequenced for a single sample for each of the clades evident from the COI topology. DNA sequence data were analysed using maximum parsimony and Bayesian inferences, while a haplotype network was constructed and an analysis of molecular variation was conducted. Gross morphological characteristics, such as the number of pre-genital leg pairs, the genital areas and colour variation in each sample locality were examined. Moreover, characters of the antennae, the shape of the main dermal papillae and male genital pad features were investigated. Topologies derived from the combined DNA analyses (COI and 18S rDNA) were congruent and revealed that P. moseleyi is a complex comprised of five genetically distinct clades. At present, these clades could not be differentiated based on morphological characters, suggesting that traditional species-discriminating characters have limited taxonomic utility. However, colour differences between the two sympatric morphs may be used to differentiate these clades. Our results indicate that cryptic speciation is present within P. moseleyi, with most of the novel detected lineages characterized by restricted geographic distribution.
Three types of sensilla occurring on the lips and on the antennae of Peripatopsis moseleyi have been investigated by scanning and transmission electron microscopy. On the lips sensory spines can be found which contain numerous cilia originating from bipolar receptor cells. They reach the tip of the spine where the cuticle is modified. The perikarya of the sensory cells, a large supporting cell with a complicated surface and a second type of receptor, form a bud-like structure and are surrounded by a layer of collagen fibrils. The second receptor cell bears apical stereocilia as well as a kinocilium which are directed towards the centre of the animal -- thus the cell appears to be turned upside down. The sensilla of the antennae are 1) sensory bristles containing two or three kinds of receptor cells, one of which bears an apical cilium and one kind of supportive cell and 2) sensory bulbs located within furrows consisting of receptor cells with branched cilia and two kinds of supportive cells which are covered by a modified thin cuticle. According to the electron microscopical findings the sensory spines on the lips are presumably chemoreceptors. The sensory bristles on the antennae can be regarded as mechanoreceptors and the sensory bulbs as chemoreceptors.
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