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Lobopodia Snodgrass, 1938 Xenusia Dzik & Krumbiegel, 1989 Diania cactiformis gen. et sp. nov. Etymology. Dian represents a linguistic abbreviation in Chinese of the Yunnan province, where the Chengjiang fossil [...], Cambrian fossil Lagerstatten preserving soft-bodied organisms have contributed much towards our understanding of metazoan origins (1-3). Lobopodians are a particularly interesting group that diversified and flourished in the Cambrian seas. Resembling 'worms with legs', they have long attracted much attention in that they may have given rise to both Onychophora (velvet worms) (4-6) and Tardigrada (water bears) (7,8),aswell astoarthropods in general (9-12). Here we describe Diania cacttiformis gen. et sp. nov. as an'armoured' lobopodian from the Chengjiang fossil Lagerstatte (Cambrian Stage 3), Yunnan, southwestern China. Although sharing features with other typical lobopodians, it is remarkable for possessing robust and probably sclerotized appendages, with what appear to be articulated elements. In terms of limb morphology it is therefore closer to the arthropod condition, to our knowledge, than any lobopodian recorded until now. Phylogenetic analysis recovers it in a derived position, close to Arthropoda; thus, it seems to belong to a grade of organization close to the point of becoming a true arthropod. Further, D.cactiformis could imply that arthropodization (sclerotization of the limbs) preceded arthrodization (sclerotization of the body). Comparing our fossils with other lobopodian appendage morphologies--see Kerygmachela (9,10), Jianshanopodia (13) and Megadicttyon (12)--reinforces the hypothesis that the group as a whole is paraphyletic, with different taxa expressing different grades of arthropodization.

Cambrian fossil Lagerstätten preserving soft-bodied organisms have contributed much towards our understanding of metazoan origins. Lobopodians are a particularly interesting group that diversified and flourished in the Cambrian seas. Resembling 'worms with legs', they have long attracted much attention in that they may have given rise to both Onychophora (velvet worms) and Tardigrada (water bears), as well as to arthropods in general. Here we describe Diania cactiformis gen. et sp. nov. as an 'armoured' lobopodian from the Chengjiang fossil Lagerstätte (Cambrian Stage 3), Yunnan, southwestern China. Although sharing features with other typical lobopodians, it is remarkable for possessing robust and probably sclerotized appendages, with what appear to be articulated elements. In terms of limb morphology it is therefore closer to the arthropod condition, to our knowledge, than any lobopodian recorded until now. Phylogenetic analysis recovers it in a derived position, close to Arthropoda; thus, it seems to belong to a grade of organization close to the point of becoming a true arthropod. Further, D. cactiformis could imply that arthropodization (sclerotization of the limbs) preceded arthrodization (sclerotization of the body). Comparing our fossils with other lobopodian appendage morphologies-see Kerygmachela, Jianshanopodia and Megadictyon-reinforces the hypothesis that the group as a whole is paraphyletic, with different taxa expressing different grades of arthropodization. [ABSTRACT FROM AUTHOR]

Replying to R. C. P. Mounce & M. Wills 476, 10.1038/nature10266 (2011); D. A. Legg et al. 476 10.1038/nature10267 (2011)We welcome the reanalyses by Mounce and Wills and Legg et al. of our paper, and although we do not fully concur with their conclusions we are pleased that Diania has reopened the debate about key stages in arthropod evolution. We accept that the position of this fossil remains sensitive to parameters of analysis and in the original publication we conceded that our best-supported tree-Diania as sister-group to (Schinderhannes + Euarthropoda)-could be subject to change, and that the 'walking cactus' may have a more basal position within the overall framework of the arthropod stem-group. These alternative treatments of our data would seem to confirm this suspicion, although we find the placement of Diania in an unresolved, and extremely basal, polytomy alongside velvet worms, tardigrades and various other lobopodians similarly problematical. We do not doubt that the authors' results are statistically well supported, but what do these cladograms tell us about the evolution of the group? Lobopodians are, by their nature, fairly simple and consequently yield few convincing synapomorphies, either with each other or with arthropods in general. As we discovered, this makes scoring a robust data matrix including both lobopodians and arthropods challenging, and we wonder whether the basal polytomies recovered here are simply due to clustering among taxa with few unequivocal apomorphies and/or much missing data. [ABSTRACT FROM AUTHOR]