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The slime of velvet worms (Onychophora) is a strong and fully biodegradable protein material, which upon ejection undergoes a fast liquid-to-solid transition to ensnare prey. However, the molecular mechanisms of slime self-assembly are still not well understood, notably because the primary structures of slime proteins are yet unknown. Combining transcriptomic and proteomic studies, the authors have obtained the complete primary sequences of slime proteins and identified key features for slime self-assembly. The high molecular weight slime proteins contain cysteine residues at the N- and C-termini that mediate the formation of multi-protein complexes via disulfide bonding. Low complexity domains in the N-termini are also identified and their propensity for liquid-liquid phase separation is established, which may play a central role in slime biofabrication. Using solid-state nuclear magnetic resonance, rigid and flexible domains of the slime proteins are mapped to specific peptide domains. The complete sequencing of major slime proteins is an important step toward sustainable fabrication of polymers inspired by the velvet worm slime.

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BACKGROUND: Onychophorans, commonly known as velvet worms, display a remarkable diversity of reproductive strategies including oviparity, and placentotrophic, lecithotrophic, matrotrophic or combined lecithotrophic/matrotrophic viviparity. In the placentotrophic species, the embryos of consecutive developmental stages are attached to the uterus via a placental stalk, suggesting they might be transported passively towards the vagina due to proximal growth and distal degeneration of tissue. However, this assumption has never been tested using specific markers. We therefore analyzed the patterns of cell proliferation and apoptosis in the genital tracts of two placentotrophic peripatids from Colombia and a non-placentotrophic peripatopsid from Australia. RESULTS: All three species show a high number of apoptotic cells in the distal portion of the genital tract near the genital opening. In the two placentotrophic species, additional apoptotic cells appear in ring-like vestigial placentation zones of late embryonic chambers. While moderate cell proliferation occurs along the entire uterus in all three species, only the two placentotrophic species show a distinct proliferation zone near the ovary as well as in the ring-like implantation zone of the first embryonic chamber. In contrast to the two placentotrophic species, the non-placentotrophic species clearly does not show such regions of high proliferation in the uterus but exhibits proliferating and apoptotic cells in the ovarian stalks. While cell proliferation mainly occurs in stalks carrying maturating oocytes, apoptosis is restricted to stalks whose oocytes have been released into the ovarian lumen. CONCLUSIONS: Our results confirm the hypothesis that the uterus of placentotrophic onychophorans grows proximally but is resorbed distally. This is supported by the detection of a proximal proliferation zone and a distal degenerative zone in the two placentotrophic species. Hence, cell turnover might be responsible for the transport of their embryos towards the vagina, analogous to a conveyor belt. Surprisingly, the distal degenerative zone is also found in the non-placentotrophic species, in which cell turnover was unexpected. These findings suggest that the distal degenerative zone is an ancestral feature of Onychophora, whereas the proximal proliferation zone might have evolved in the last common ancestor of the placentotrophic Peripatidae.

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BACKGROUND: NK genes are a group of homeobox transcription factors that are involved in various molecular pathways across bilaterians. They are typically divided into two subgroups, the NK cluster (NKC) and NK-linked genes (NKL). While the NKC genes have been studied in various bilaterians, corresponding data of many NKL genes are missing to date. To further investigate the ancestral roles of NK family genes, we analyzed the expression patterns of NKL genes in the onychophoran Euperipatoides rowelli. RESULTS: The NKL gene complement of E. rowelli comprises eight genes, including BarH, Bari, Emx, Hhex, Nedx, NK2.1, vax and NK2.2, of which only NK2.2 was studied previously. Our data for the remaining seven NKL genes revealed expression in different structures associated with the developing nervous system in embryos of E. rowelli. While NK2.1 and vax are expressed in distinct medial regions of the developing protocerebrum early in development, BarH, Bari, Emx, Hhex and Nedx are expressed in late developmental stages, after all major structures of the nervous system have been established. Furthermore, BarH and Nedx are expressed in distinct mesodermal domains in the developing limbs. CONCLUSIONS: Comparison of our expression data to those of other bilaterians revealed similar patterns of NK2.1, vax, BarH and Emx in various aspects of neural development, such as the formation of anterior neurosecretory cells mediated by a conserved molecular mechanism including NK2.1 and vax, and the development of the central and peripheral nervous system involving BarH and Emx. A conserved role in neural development has also been reported from NK2.2, suggesting that the NKL genes might have been primarily involved in neural development in the last common ancestor of bilaterians or at least nephrozoans (all bilaterians excluding xenacoelomorphs). The lack of comparative data for many of the remaining NKL genes, including Bari, Hhex and Nedx currently hampers further evolutionary conclusions. Hence, future studies should focus on the expression of these genes in other bilaterians, which would provide a basis for comparative studies and might help to better understand the role of NK genes in the diversification of bilaterians.

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BACKGROUND: Understanding the evolution and development of morphological traits of the last common bilaterian ancestor is a major goal of the evo-devo discipline. The reconstruction of this "urbilaterian" is mainly based on comparative studies of common molecular patterning mechanisms in recent model organisms. The NK homeobox genes are key players in many of these molecular pathways, including processes regulating mesoderm, heart and neural development. Shared features seen in the expression patterns of NK genes have been used to determine the ancestral bilaterian characters. However, the commonly used model organisms provide only a limited view on the evolution of these molecular pathways. To further investigate the ancestral roles of NK cluster genes, we analyzed their expression patterns in the onychophoran Euperipatoides rowelli. RESULTS: We identified nine transcripts of NK cluster genes in E. rowelli, including single copies of NK1, NK3, NK4, NK5, Msx, Lbx and Tlx, and two copies of NK6. All of these genes except for NK6.1 and NK6.2 are expressed in different mesodermal organs and tissues in embryos of E. rowelli, including the anlagen of somatic musculature and the heart. Furthermore, we found distinct expression patterns of NK3, NK5, NK6, Lbx and Msx in the developing nervous system. The same holds true for the NKL gene NK2.2, which does not belong to the NK cluster but is a related gene playing a role in neural patterning. Surprisingly, NK1, Msx and Lbx are additionally expressed in a segment polarity-like pattern early in development-a feature that has been otherwise reported only from annelids. CONCLUSION: Our results indicate that the NK cluster genes were involved in mesoderm and neural development in the last common ancestor of bilaterians or at least nephrozoans (i.e., bilaterians to the exclusion of xenacoelomorphs). By comparing our data from an onychophoran to those from other bilaterians, we critically review the hypothesis of a complex "urbilaterian" with a segmented body, a pulsatile organ or heart, and a condensed mediolaterally patterned nerve cord.

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Understanding the origin and evolution of arthropods requires examining their closest outgroups, the tardigrades (water bears) and onychophorans (velvet worms). Despite the rise of molecular techniques, the phylogenetic positions of tardigrades and onychophorans in the panarthropod tree (onychophorans + tardigrades + arthropods) remain unresolved. Hence, these methods alone are currently insufficient for clarifying the panarthropod topology. Therefore, the evolution of different morphological traits, such as one of the most intriguing features of panarthropods-their nervous system-becomes essential for shedding light on the origin and evolution of arthropods and their relatives within the Panarthropoda. In this review, we summarise current knowledge of the evolution of panarthropod nervous and visual systems. In particular, we focus on the evolution of segmental ganglia, the segmental identity of brain regions, and the visual system from morphological and developmental perspectives. In so doing, we address some of the many controversies surrounding these topics, such as the homology of the onychophoran eyes to those of arthropods as well as the segmentation of the tardigrade brain. Finally, we attempt to reconstruct the most likely state of these systems in the last common ancestors of arthropods and panarthropods based on what is currently known about tardigrades and onychophorans.

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BACKGROUND: Apoptosis is involved in various developmental processes, including cell migration and tissue and organ formation. Some of these processes are conserved across metazoans, while others are specific to particular taxa. Although the patterns of apoptosis have been investigated in arthropods, no corresponding data are available from one of their closest relatives, the Onychophora (velvet worms). RESULTS: We analyzed the patterns of apoptosis in embryos of two onychophoran species: the lecithotrophic/matrotrophic viviparous peripatopsid Euperipatoides rowelli, and the placentotrophic viviparous peripatid Principapillatus hitoyensis. Our data show that apoptosis occurs early in development and might be responsible for the degeneration of extra-embryonic tissues. Moreover, apoptosis might be involved in the morphogenesis of the ventral and preventral organs in both species and occurs additionally in the placental stalk of P. hitoyensis. CONCLUSIONS: Despite the different developmental modes in these onychophoran species, our data suggest that patterns of apoptosis are conserved among onychophorans. While apoptosis in the dorsal extra-embryonic tissue might contribute to dorsal closure-a process also known from arthropods-the involvement of apoptosis in ventral closure might be unique to onychophorans. Apoptosis in the placental stalk of P. hitoyensis is most likely a derived feature of the placentotrophic onychophorans. Developmental Dynamics 246:403-416, 2017. © 2017 Wiley Periodicals, Inc.

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The geological age of the onychophoran crown-group, and when the group came onto land, have been sources of debate. Although stem-group Onychophora have been identified from as early as the Cambrian, the sparse record of terrestrial taxa from before the Cretaceous is subject to contradictory interpretations. A Late Carboniferous species from the Mazon Creek biota of the USA, Helenodora inopinata, originally interpreted as a crown-group onychophoran, has recently been allied to early Cambrian stem-group taxa. Here we describe a fossil species from the Late Carboniferous Montceau-les-Mines Lagerstätte, France, informally referred to as an onychophoran for more than 30 years. The onychophoran affinities of Antennipatus montceauensis gen. nov., sp. nov. are indicated by the form of the trunk plicae and the shape and spacing of their papillae, details of antennal annuli, and the presence of putative slime papillae. The poor preservation of several key systematic characters for extant Onychophora, however, prohibits the precise placement of the Carboniferous fossil in the stem or crown of the two extant families, or the onychophoran stem-group as a whole. Nevertheless, A. montceauensis is the most compelling candidate to date for a terrestrial Paleozoic onychophoran.

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Onychophora have undergone a new wave of taxonomic revisions in the last three years. After a recent revision, only two species of Macroperipatus are registered from Brazil: Macroperipatus ohausi and Macroperipatus geayi. The former was only the second species of Onychophora to be described from Brazil, and is herein redescribed, illustrated, and its taxonomic status revised. Macroperipatus ohausi had only been collected at the type locality, Petrópolis, state of Rio de Janeiro, but has not been found there since its discovery. In 2009 we collected two specimens of this species in an Atlantic rain forest fragment in Nova Iguaçu in RPPN dos Petroleiros (also state of Rio de Jane iro). The color of the new specimens was interpreted and described based on the NBS/ISCC System of Color Designation, and corresponds only weakly to that described in earlier publications on M. ohausi. The identification of M. ohausi was based solely on its morphology and compared with its original description. In addition, a female syntype of M. ohausi deposited in the Zoologisches Museum (Hamburg) was examined. We reinvestigated its external morphology and concluded that the dorsal papillae have been misinterpreted in M. ohausi in previous studies of its integument. The new specimens examined are conspecific with M. ohausi mainly by having conical primary papillae, different sized accessory papillae, and by the number of legs. Our material resembles the original description of M. ohausi, for example, in spinous pad and nephridial tubercles, even though these features are not represented in the original description and rede- scription of M. ohausi; these features are further detailed here. We concluded that the dorsal papillae morphology of M. ohausi, shares diagnostic characters, for example, with representatives of the genera Peripatus and Epiperipatus. The dorsal papillae are rounded and not square as in the original description and redescription. Another argument that supports our conclusion is that the RPPN dos Petroleiros, the locality where the new samples were collected, belongs to the same mountain chain and Atlantic mosaic as the original material of M. ohausi. Furthermore, a male of M. ohausi is described here for the first time. Based on our morphological data, we transfered this species to the genus Epiperipatus, proposing a new combination, E. ohausi.

Onychophora experimentó una nueva serie de revisiones taxonómicas en los últimos tres años. Después de una reciente revisión, sólo dos especies de Macroperipatus fueron registradas para Brasil: Macroperipatus ohausi y Macroperipatus geayi. La primera fue solo la segunda especie de Onychophora en ser descrita en Brasil y aquí es redescrita, ilustrada, y su estatus taxonómico revisado. Macroperipatus ohausi sólo se había recolectado en la localidad tipo, Petropolis, Estado de Rio de Janeiro, pero no se ha encontrado allí desde su descubrimiento. En 2009, recolectamos dos ejemplares de esta especie en un fragmento de la ‘Mata Atlantica’ en Nova Iguaçu en el RPPN de los Petroleiros (también en el estado de Rio de Janeiro). El color de los ejemplares nuevos fue interpretado y descrito, basado en el sistema NBS System/ISCC de designación de colores, y correspondió débilmente al descrito en publicaciones anteriores sobre M. ohausi. La identificación de M. ohausi se basó únicamente en su morfología, en comparación con la descripción original. Además, se examinó un sintipo hembra de M. ohausi depositado en Zoologisches Museum (Hamburgo). Nosotros reinvestigamos su morfología externa y concluimos que las papilas dorsales fueron mal interpretadas en M. ohausi en los estudios previos de su integumento. Los nuevos especímenes examinados son coespecíficos con M. ohausi principalmente por tener las papilas primarias cónicas, diferente tamaño de las papilas accesorias, y por el número de patas. Nuestro material se asemeja a la descripción original de M. ohausi, por ejemplo, la almohadilla espinosa y tubérculos nefridiales, aunque estas características no están representadas en la descripción original y redescripcion de M. ohausi, estas características también se detallan aquí. Llegamos a la conclusión de que la morfología de las papilas dorsales de M. ohausi, comparte caracteres de diagnóstico, por ejemplo, con los representantes de los géneros Peripatus y Epiperipatus. Las papilas dorsales son redondeadas y no cuadradas como en la descripción original y redescripción. Otro argumento que apoya nuestra conclusión es que la RPPN dos Petroleiros, la ubicación en la que se recogieron las nuevas muestras, pertenece a la misma cadena de montañas y al mosaico Atlántico, tal como el material original de M. ohausi. Por otra parte, se describe aquí por primera vez un macho de M. ohausi. Basado en nuestros datos morfológicos, transferimos esta especie al género Epiperipatus, que propone una nueva combinación, E. ohausi.

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The current distributions of widespread groups of terrestrial animals and plants are supposedly the result of a mixture of either vicariance owing to continental split or more recent trans-oceanic dispersal. For organisms exhibiting a vicariant biogeographic pattern-achieving their current distribution by riding on the plates of former supercontinents-this view is largely inspired by the belief that Pangaea lacked geographical or ecological barriers, or that extinctions and dispersal would have erased any biogeographic signal since the early Mesozoic. We here present a time-calibrated molecular phylogeny of Onychophora (velvet worms), an ancient and exclusively terrestrial panarthropod group distributed throughout former Pangaean landmasses. Our data not only demonstrate that trans-oceanic dispersal does not need be invoked to explain contemporary distributions, but also reveal that the early diversification of the group pre-dates the break-up of Pangaea, maintaining regionalization even in landmasses that have remained contiguous throughout the history of the group. These results corroborate a growing body of evidence from palaeontology, palaeogeography and palaeoclimatic modelling depicting ancient biogeographic regionalization over the continuous landmass of Pangaea.

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The gene decapentaplegic (dpp) and its homologs are essential for establishing the dorsoventral body axis in arthropods and vertebrates. However, the expression of dpp is not uniform among different arthropod groups. While this gene is expressed along the dorsal body region in insects, its expression occurs in a mesenchymal group of cells called cumulus in the early spider embryo. A cumulus-like structure has also been reported from centipedes, suggesting that it might be either an ancestral feature of arthropods or a derived feature (=synapomorphy) uniting the chelicerates and myriapods. To decide between these two alternatives, we analysed the expression patterns of a dpp ortholog in a representative of one of the closest arthropod relatives, the onychophoran Euperipatoides rowelli. Our data revealed unique expression patterns in the early mesoderm anlagen of the antennal segment and in the dorsal and ventral extra-embryonic tissue, suggesting a divergent role of dpp in these tissues in Onychophora. In contrast, the expression of dpp in the dorsal limb portions resembles that in arthropods, except that it occurs in the mesoderm rather than in the ectoderm of the onychophoran limbs. A careful inspection of embryos of E. rowelli revealed no cumulus-like accumulation of dpp expressing cells at any developmental stage, suggesting that this feature is either a derived feature of chelicerates or a synapomorphy uniting the chelicerates and myriapods.

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Onychophorans, or velvet worms, are poorly known and rare animals. Here we report the discovery of a new species that is also the largest onychophoran found so far, a 22cm long female from the Caribbean coastal forest of Costa Rica. Specimens were examined with Scanning Electron Microscopy; Peripatus solorzanoi sp. nov., is diagnosed as follows: primary papillae convex and conical with rounded bases, with more than 18 scale ranks. Apical section large, spherical, with a basal diameter of at least 20 ranks. Apical piece with 6-7 scale ranks. Outer blade 1 principal tooth, 1 accessory tooth, 1 vestigial accessory tooth (formula: 1/1/1); inner blade 1 principal tooth, 1 accessory tooth, 1 rudimentary accessory tooth, 9 to 10 denticles (formula: 1/1/1/9-10). Accessory tooth blunt in both blades. Four pads in the fourth and fifth oncopods; 4th. pad arched. The previously unknown mechanism by which onychophorans weave their adhesive is simple: muscular action produces a swinging movement of the adhesive-spelling organs; as a result, the streams cross in mid air, weaving the net. Like all onychophorans, P. solorzanoi is a rare species: active protection of the habitat of the largest onychophoran ever described, is considered urgent. Rev. Biol. Trop. 58 (4): 1127-1142. Epub 2010 December 01.

Los onicóforos o "peripatos" son animales escasos y poco conocidos. Aquí informamos el descubrimiento del onicóforo más grandes conocido, una hembra de 22cm de longitud del bosque costero caribeño de Costa Rica. Analizamos los especímenes con microscopia electrónica de barrido. La nueva especie, Peripatus solorzanoi, sp. nov. se caracteriza así: papilas primarias convexas y cónicas, con bases redondeadas y más de 18 filas de escamas de alto. Sección apical grande y esférica, con diámetro basal de al menos 20 filas. Parte apical con 6-7 filas de escamas de alto. Fórmula de lámina mandibular externa 1/1/1, lámina interna: 1/1/1/9-10. Diente accesorio romo en ambas láminas. Cuatro almohadillas en cuarto y quinto oncopodios; cuarta almohadilla arqueada. Describimos el mecanismo, previamente desconocido, mediante el cual tejen su red los onicóforos, usando fotografías para mostrar que es de naturaleza muscular. Como todos los demás onicóforos, P. solorzanoi es una especie escasa: consideramos urgente la protección del hábitat del onicóforo más grande del mundo.

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Velvet worm taxonomy from Santander, Colombia and thermogravimetry, differential scanning calorimetry and infrared spectroscopy of the adhesive secretion (Onychophora: Peripatidae). Onychophoran worms are terrestrial organisms that have changed relatively little since the mid-Cambrian. We collected Macroperipatus geagy in coffee plantations at "Hacienda El Roble", Santander, Colombia, and here redescribe the species based on 15 individuals. A digital three-dimensional reconstruction of the ventral side of the body indicates that the primary and accessory papillae lack a defined distribution pattern. Diagnostic characters: one main tooth and one accessory tooth in the outer jaw, and one main tooth, one accessory tooth and seven denticles in the internal jaw. Measurements: length (X=45.66 mm; SD=26.10), weight (X= 0.95 g; SD= 2.21) and number of lobopods (X= 28.13 pairs; SD= 1.30). We present a taxonomic key for six species of Macroperipatus. The liquid adhesive secretion lost 60% of the initial weight at 70 oC (solid: 13% close to 90 oC). The stability phase of the liquid secretion was within 90-280 oC (100 oC -205 oC in the solid secretion). The starting degradation temperature of the sample was 355 oC. Heat flow changes in the solid and liquid secretions were confirmed by the sample behavior during thermogravimetric analysis. The percentage of β sheets calculated by infrared spectrum was 59%. In comparison with Nephila spiders, the onychophoran secretion lost more weight and entered the phase of degradation at lower temperatures. This secondary structure of proteins gives the onychophoran adhesive secretion a tensile strength and extensibility similar to those of the silk produced by spiders for prey-capture. Rev. Biol. Trop. 57 (3): 567-588. Epub 2009 September 30.

Redescribimos taxonómicamente el gusano Macroperipatus geagy Bouvier 1899, a partir de 15 especímenes recolectados en los cafetales de hacienda El Roble, Santander, Colombia. De acuerdo con la reconstrucción en tres dimensiones de la superficie dorsal del cuerpo, las papilas primarias y accesorias de M. geagy se distribuyen sin formar un patrón determinado. Características diagnósticas: un diente accesorio y un diente principal en la mandíbula externa; y un diente principal, un diente accesorio y siete dentículos en la sierra de la mandíbula interna. Cuerpo: longitud (X=45.66; S=26.10 mm), peso (X= 0.95; S= 2.21) y pares de lobopodos (X= 28.13; S= 1.30). Se elaboró una clave para seis especies de Macroperipatus. La secreción adhesiva en estado líquido perdió 60% del peso inicial al alcanzar los 70 ºC, la muestra sólida perdió el 13% del peso cerca de los 90 ºC, la fase de estabilidad térmica de la secreción estuvo entre los 90 y 280 ºC en la secreción líquida y entre los 100 y 205 ºC en la sólida. La temperatura de inicio de la degradación de las muestras se registró a los 355 ºC. En comparación con la araña Nephila sp., el onicóforo perdió mayor porcentaje de peso y alcanzó la fase de degradación a temperaturas más bajas. Los cambios en el flujo de calor en la secreción adhesiva sólida y líquida de M. geagy fueron confirmados con el comportamiento de las muestras en el análisis de termogravimetría. La proporción de láminas beta calculado en el espectro infrarrojo de la secreción adhesiva fue del 59%. La presencia de este tipo de conformación de la estructura secundaria de las proteínas en la secreción adhesiva de M. geagy conferiría extensibilidad y resistencia a la tracción, en similitud con las fibras de seda tejidas por las arañas para depredación.

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