A Carboniferous Non-Onychophoran Lobopodian Reveals Long-Term Survival of a Cambrian Morphotype
ABSTRACT Lobopodians, a nonmonophyletic assemblage of worm-shaped soft-bodied animals most closely related to arthropods, show two major morphotypes: long-legged and short-legged forms. The morphotype with stubby, conical legs has a long evolutionary history, from the early Cambrian  through the Carboniferous [2, 3], including the living onychophorans and tardigrades [4-6]. Species with tubular lobopods exceeding the body diameter have been reported exclusively from the Cambrian [7-12]; the three-dimensionally preserved Orstenotubulus evamuellerae from the uppermost middle Cambrian "Orsten" (Sweden) is the youngest long-legged lobopodian reported thus far . Here we describe a new long-legged lobopodian, Carbotubulus waloszeki gen. et sp. nov., from Mazon Creek, Illinois, USA (∼296 million years ago) . This first post-Cambrian long-legged lobopodian extends the range of this morphotype by about 200 million years. The three-dimensionally preserved specimen differs significantly from the associated short-legged form Ilyodes inopinata , of which we also present new head details. The discovery of a Carboniferous long-legged lobopodian provides a more striking example of the long-term survival of Cambrian morphotypes than, for example, the occurrence of a Burgess Shale-type biota in the Ordovician of Morocco  and dampens the effect of any major extinction of taxa at the end of the middle Cambrian [15, 16].
Full-textDOI: · Available from: Georg Mayer, Aug 29, 2015
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- "Within the Ecdysozoa, Onychophora is commonly united with Tardigrada and Arthropoda in the clade Panarthropoda, although the exact relationship among these three animal groups remains unresolved (Mayer and Whitington 2009a; Rota-Stabelli et al. 2010; Campbell et al. 2011; Nielsen 2012; Mayer et al. 2013a, 2013b). In contrast to their relatives, the arthropods and tardigrades, the overall anatomy of the onychophoran body has remained largely unchanged since the Early Cambrian and extant onychophorans strikingly resemble the habitus of fossil lobopodians, a non-monophyletic assemblage of stem-group representatives of Panarthropoda, Onychophora, Tardigrada, and/or Arthropoda (e.g., Maas et al. 2007; Ma et al. 2009; Liu et al. 2011; Haug et al. 2012; Ou et al. 2012; Smith and Ortega-Hernández 2014). Herein we provide an outline of our current knowledge about the feeding mechanisms, functional morphology, and elementary composition of the jaws in Onychophora. "
ABSTRACT: Onychophorans are carnivorous, terrestrial invertebrates that occur in tropical and temperate forests of the Southern Hemisphere and around the Equator. Together with tardigrades, onychophorans are regarded as one of the closest relatives of arthropods. One of the most peculiar features of onychophorans is their hunting and feeding behavior. These animals secrete a sticky slime, which is ejected via a pair of slime-papillae, to entangle the prey. After the prey has been immobilized, its cuticle is punctured using a pair of jaws located within the mouth. These jaws constitute internalized appendages of the second body segment and are innervated by the deutocerebrum; thus, they are homologous to the chelicerae of chelicerates, and to the (first) antennae of myriapods, crustaceans, and insects. The jaws are also serial homologs of the paired claws associated with each walking limb of the trunk. The structure of the jaws is similar in representatives of the two major onychophoran subgroups, the Peripatidae and Peripatopsidae. Each jaw is characterized by an outer and an inner blade; while the outer blade consists only of a large principal tooth and up to three accessory teeth, the inner blade bears numerous additional denticles. These denticles are separated from the remaining part of the inner jaw by a diastema and a soft membrane only in peripatids. The onychophoran jaws are associated with large apodemes and specialized muscles that enable their movement. In contrast to the mandibles of arthropods, the onychophoran jaws are moved along, rather than perpendicular to, the main axis of the body. Our elemental analysis reveals an increased incorporation of calcium at the tip of each blade, which might provide rigidity, whereas there is no evidence for incorporation of metal or prominent mineralization. Stability of the jaw might be further facilitated by the cone-in-cone organization of its cuticle, as each blade consists of several stacked, cuticular elements. In this work, we summarize current knowledge on the jaws of onychophorans, which are a characteristic feature of these animals. © The Author 2015. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: firstname.lastname@example.org.Integrative and Comparative Biology 03/2015; 2(55):217–227. DOI:10.1093/icb/icv004 · 2.97 Impact Factor
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- "Many authors count tardigrades and onychophorans as extant lobopods (e.g. Waloszek et al., 2007; Haug et al., 2012 and further references therein). "
ABSTRACT: This review summarizes some major events in the evolution of body plans along the backbone of the arthropod tree, with a special focus on the origin of insects. The incompatibility among recent molecular phylogenies motivates a discussion about possible causes for failures: there is a worrisome lack of information in alignments, which can be visualized with spectra of split-supporting positions, and there are systematic errors occurring even when using correct models in maximum likelihood methods (Kück et al, this book). Currently, these problems cannot be avoided. Combining information from the fossil record and from extant arthropods, the morphology-based evolutionary scenario leads from worm-like stem-lineage arthropods via first euarthropods to the crown group of Mandibulata. The evolution of the mandibulate head is well documented in the Cambrian Orsten fossils. The evolution within crustaceans is also the evolution that leads to characters of the bauplan of myriapods and insects. It is argued that morphologically myriapods do not fit to the base of the mandibulatan tree and that this placement is also not plausible from a paleontological point of view. Available morphological evidence suggests that myriapods are the sistergroup to Hexapoda and that tracheates evolved from a marine ancestor that was similar in many ways to Remipedia. In the extant fauna, the Remipedia are the sistergroup of Tracheata.Deep Metazoan Phylogeny: The Backbone of the Tree of Life, 1 edited by J.W. Wägele, T. Bartolomaeus, 02/2014: chapter Arthropod phylogeny and the origin of Tracheata (= Atelocerata) from Remipedia-like ancestors.: pages 285-341; DeGruyter., ISBN: 9783110262636
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- "During development, they arise from segmental thickenings of the embryonic ectoderm and persist in adults as sclerotized structures that serve as attachment sites for segmental limb depressor muscles. Whether the ventral and preventral organs are a derived feature of Onychophora or whether they are remnants of sclerotized, vaulted body rings described from fossil lobopodians  – putative stem-lineage representatives of Onychophora, Tardigrada, Arthropoda and/or Panarthropoda [49,50] – is open for discussion. "
ABSTRACT: The so-called ventral organs are amongst the most enigmatic structures in Onychophora (velvet worms). They were described as segmental, ectodermal thickenings in the onychophoran embryo, but the same term has also been applied to mid-ventral, cuticular structures in adults, although the relationship between the embryonic and adult ventral organs is controversial. In the embryo, these structures have been regarded as anlagen of segmental ganglia, but recent studies suggest that they are not associated with neural development. Hence, their function remains obscure. Moreover, their relationship to the anteriorly located preventral organs, described from several onychophoran species, is also unclear. To clarify these issues, we studied the anatomy and development of the ventral and preventral organs in several species of Onychophora. Our anatomical data, based on histology, and light, confocal and scanning electron microscopy in five species of Peripatidae and three species of Peripatopsidae, revealed that the ventral and preventral organs are present in all species studied. These structures are covered externally with cuticle that forms an internal, longitudinal, apodeme-like ridge. Moreover, phalloidin-rhodamine labelling for f-actin revealed that the anterior and posterior limb depressor muscles in each trunk and the slime papilla segment attach to the preventral and ventral organs, respectively. During embryonic development, the ventral and preventral organs arise as large segmental, paired ectodermal thickenings that decrease in size and are subdivided into the smaller, anterior anlagen of the preventral organs and the larger, posterior anlagen of the ventral organs, both of which persist as paired, medially-fused structures in adults. Our expression data of the genes Delta and Notch from embryos of Euperipatoides rowelli revealed that these genes are expressed in two, paired domains in each body segment, corresponding in number, position and size with the anlagen of the ventral and preventral organs. Our findings suggest that the ventral and preventral organs are a common feature of onychophorans that serve as attachment sites for segmental limb depressor muscles. The origin of these structures can be traced back in the embryo as latero-ventral segmental, ectodermal thickenings, previously suggested to be associated with the development of the nervous system.Frontiers in Zoology 12/2013; 10(1):73. DOI:10.1186/1742-9994-10-73 · 2.30 Impact Factor