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Gerhard Scholtz - One of the best experts on this subject based on the ideXlab platform.
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comparison of ventral organ development across Pycnogonida arthropoda chelicerata provides evidence for a plesiomorphic mode of late neurogenesis in sea spiders and myriapods
BMC Evolutionary Biology, 2018Co-Authors: Georg Brenneis, Gerhard Scholtz, Barbara S. BeltzAbstract:Comparative studies of neuroanatomy and neurodevelopment provide valuable information for phylogenetic inference. Beyond that, they reveal transformations of neuroanatomical structures during animal evolution and modifications in the developmental processes that have shaped these structures. In the extremely diverse Arthropoda, such comparative studies contribute with ever-increasing structural resolution and taxon coverage to our understanding of nervous system evolution. However, at the neurodevelopmental level, in-depth data remain still largely confined to comparably few laboratory model organisms. Therefore, we studied postembryonic neurogenesis in six species of the bizarre Pycnogonida (sea spiders), which – as the likely sister group of all remaining chelicerates – promise to illuminate neurodevelopmental changes in the chelicerate lineage. We performed in vivo cell proliferation experiments with the thymidine analogs 5-bromo-2′-deoxyuridine and 5-ethynl-2′-deoxyuridine coupled to fluorescent histochemical staining and immunolabeling, in order to compare ventral nerve cord anatomy and to localize and characterize centers of postembryonic neurogenesis. We report interspecific differences in the architecture of the subesophageal ganglion (SEG) and show the presence of segmental “ventral organs” (VOs) that act as centers of neural cell production during gangliogenesis. These VOs are either incorporated into the ganglionic soma cortex or found on the external ganglion surface. Despite this difference, several shared features support homology of the two VO types, including (1) a specific arrangement of the cells around a small central cavity, (2) the presence of asymmetrically dividing neural stem cell-like precursors, (3) the migration of newborn cells along corresponding pathways into the cortex, and (4) the same VO origin and formation earlier in development. Evaluation of our findings relative to current hypotheses on pycnogonid phylogeny resolves a bipartite SEG and internal VOs as plesiomorphic conditions in pycnogonids. Although chelicerate taxa other than Pycnogonida lack comparable VOs, they are a characteristic feature of myriapod gangliogenesis. Accordingly, we propose internal VOs with neurogenic function to be part of the ground pattern of Arthropoda. Further, our findings illustrate the importance of dense sampling in old arthropod lineages – even if as gross-anatomically uniform as Pycnogonida – in order to reliably differentiate plesiomorphic from apomorphic neurodevelopmental characteristics prior to outgroup comparison.
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Comparison of ventral organ development across Pycnogonida (Arthropoda, Chelicerata) provides evidence for a plesiomorphic mode of late neurogenesis in sea spiders and myriapods
BMC, 2018Co-Authors: Georg Brenneis, Gerhard Scholtz, Barbara S. BeltzAbstract:Abstract Background Comparative studies of neuroanatomy and neurodevelopment provide valuable information for phylogenetic inference. Beyond that, they reveal transformations of neuroanatomical structures during animal evolution and modifications in the developmental processes that have shaped these structures. In the extremely diverse Arthropoda, such comparative studies contribute with ever-increasing structural resolution and taxon coverage to our understanding of nervous system evolution. However, at the neurodevelopmental level, in-depth data remain still largely confined to comparably few laboratory model organisms. Therefore, we studied postembryonic neurogenesis in six species of the bizarre Pycnogonida (sea spiders), which – as the likely sister group of all remaining chelicerates – promise to illuminate neurodevelopmental changes in the chelicerate lineage. Results We performed in vivo cell proliferation experiments with the thymidine analogs 5-bromo-2′-deoxyuridine and 5-ethynl-2′-deoxyuridine coupled to fluorescent histochemical staining and immunolabeling, in order to compare ventral nerve cord anatomy and to localize and characterize centers of postembryonic neurogenesis. We report interspecific differences in the architecture of the subesophageal ganglion (SEG) and show the presence of segmental “ventral organs” (VOs) that act as centers of neural cell production during gangliogenesis. These VOs are either incorporated into the ganglionic soma cortex or found on the external ganglion surface. Despite this difference, several shared features support homology of the two VO types, including (1) a specific arrangement of the cells around a small central cavity, (2) the presence of asymmetrically dividing neural stem cell-like precursors, (3) the migration of newborn cells along corresponding pathways into the cortex, and (4) the same VO origin and formation earlier in development. Conclusions Evaluation of our findings relative to current hypotheses on pycnogonid phylogeny resolves a bipartite SEG and internal VOs as plesiomorphic conditions in pycnogonids. Although chelicerate taxa other than Pycnogonida lack comparable VOs, they are a characteristic feature of myriapod gangliogenesis. Accordingly, we propose internal VOs with neurogenic function to be part of the ground pattern of Arthropoda. Further, our findings illustrate the importance of dense sampling in old arthropod lineages – even if as gross-anatomically uniform as Pycnogonida – in order to reliably differentiate plesiomorphic from apomorphic neurodevelopmental characteristics prior to outgroup comparison
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The ‘ventral organs’ of Pycnogonida (Arthropoda) are neurogenic niches of late embryonic and post-embryonic nervous system development. PLoS One. 2014;9(4):e95435. doi
2016Co-Authors: Georg Brenneis, Gerhard ScholtzAbstract:Early neurogenesis in arthropods has been in the focus of numerous studies, its cellular basis, spatio-temporal dynamics and underlying genetic network being by now comparably well characterized for representatives of chelicerates, myriapods, hexapods and crustaceans. By contrast, neurogenesis during late embryonic and/or post-embryonic development has received less attention, especially in myriapods and chelicerates. Here, we apply (i) immunolabeling, (ii) histology and (iii) scanning electron microscopy to study post-embryonic ventral nerve cord development in Pseudopallene sp., a representative of the sea spiders (Pycnogonida), the presumable sister group of the remaining chelicerates. During early post-embryonic development, large neural stem cells give rise to additional ganglion cell material in segmentally paired invaginations in the ventral ectoderm. These ectodermal cell regions – traditionally designated as ‘ventral organs ’ – detach from the surface into the interior and persist as apical cell clusters on the ventral ganglion side. Each cluster is a post-embryonic neurogenic niche that features a tiny central cavity and initially still houses larger neural stem cells. The cluster stays connected to the underlying ganglionic somata cortex via an anterior and a posterior cell stream. Cell proliferation remains restricted to the cluster and streams, and migration of newly produced cells along the streams seems to account for increasing ganglion cell numbers in the cortex. The pycnogonid cluster-stream-systems show striking similarities to the life-long neurogenic system of decapod crustaceans, and due to their close vicinity to glomerulus-like neuropils, we conside
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serotonin immunoreactivity in the ventral nerve cord of Pycnogonida support for individually identifiable neurons as ancestral feature of the arthropod nervous system
BMC Evolutionary Biology, 2015Co-Authors: Georg Brenneis, Gerhard ScholtzAbstract:The arthropod ventral nerve cord features a comparably low number of serotonin-immunoreactive neurons, occurring in segmentally repeated arrays. In different crustaceans and hexapods, these neurons have been individually identified and even inter-specifically homologized, based on their soma positions and neurite morphologies. Stereotypic sets of serotonin-immunoreactive neurons are also present in myriapods, whereas in the investigated chelicerates segmental neuron clusters with higher and variable cell numbers have been reported. This led to the suggestion that individually identifiable serotonin-immunoreactive neurons are an apomorphic feature of the Mandibulata. To test the validity of this neurophylogenetic hypothesis, we studied serotonin-immunoreactivity in three species of Pycnogonida (sea spiders). This group of marine arthropods is nowadays most plausibly resolved as sister group to all other extant chelicerates, rendering its investigation crucial for a reliable reconstruction of arthropod nervous system evolution. In all three investigated pycnogonids, the ventral walking leg ganglia contain different types of serotonin-immunoreactive neurons, the somata of which occurring mostly singly or in pairs within the ganglionic cortex. Several of these neurons are readily and consistently identifiable due to their stereotypic soma position and characteristic neurite morphology. They can be clearly homologized across different ganglia and different specimens as well as across the three species. Based on these homologous neurons, we reconstruct for their last common ancestor (presumably the pycnogonid stem species) a minimal repertoire of at least seven identified serotonin-immunoreactive neurons per hemiganglion. Beyond that, each studied species features specific pattern variations, which include also some neurons that were not reliably labeled in all specimens. Our results unequivocally demonstrate the presence of individually identifiable serotonin-immunoreactive neurons in the pycnogonid ventral nerve cord. Accordingly, the validity of this neuroanatomical feature as apomorphy of Mandibulata is questioned and we suggest it to be ancestral for arthropods instead. The pronounced disparities between the segmental pattern in pycnogonids and the one of studied euchelicerates call for denser sampling within the latter taxon. By contrast, overall similarities between the pycnogonid and myriapod patterns may be indicative of single cell homologies in these two taxa. This notion awaits further substantiation from future studies.
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The ‘Ventral Organs’ of Pycnogonida (Arthropoda) Are Neurogenic Niches of Late Embryonic and Post-Embryonic Nervous System Development
2014Co-Authors: Georg Brenneis, Gerhard ScholtzAbstract:Early neurogenesis in arthropods has been in the focus of numerous studies, its cellular basis, spatio-temporal dynamics and underlying genetic network being by now comparably well characterized for representatives of chelicerates, myriapods, hexapods and crustaceans. By contrast, neurogenesis during late embryonic and/or post-embryonic development has received less attention, especially in myriapods and chelicerates. Here, we apply (i) immunolabeling, (ii) histology and (iii) scanning electron microscopy to study post-embryonic ventral nerve cord development in Pseudopallene sp., a representative of the sea spiders (Pycnogonida), the presumable sister group of the remaining chelicerates. During early post-embryonic development, large neural stem cells give rise to additional ganglion cell material in segmentally paired invaginations in the ventral ectoderm. These ectodermal cell regions – traditionally designated as ‘ventral organs’ – detach from the surface into the interior and persist as apical cell clusters on the ventral ganglion side. Each cluster is a post-embryonic neurogenic niche that features a tiny central cavity and initially still houses larger neural stem cells. The cluster stays connected to the underlying ganglionic somata cortex via an anterior and a posterior cell stream. Cell proliferation remains restricted to the cluster and streams, and migration of newly produced cells along the streams seems to account for increasing ganglion cell numbers in the cortex. The pycnogonid cluster-stream-systems show striking similarities to the life-long neurogenic system of decapod crustaceans, and due to their close vicinity to glomerulus-like neuropils, we consider their possible involvement in post-embryonic (perhaps even adult) replenishment of olfactory neurons – as in decapods. An instance of a potentially similar post-embryonic/adult neurogenic system in the arthropod outgroup Onychophora is discussed. Additionally, we document two transient posterior ganglia in the ventral nerve cord of Pseudopallene sp. and evaluate this finding in light of the often discussed reduction of a segmented ‘opisthosoma’ during pycnogonid evolution.
Georg Brenneis - One of the best experts on this subject based on the ideXlab platform.
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First description of epimorphic development in Antarctic Pallenopsidae (Arthropoda, Pycnogonida) with insights into the evolution of the four-articled sea spider cheliphore
Zoological Letters, 2019Co-Authors: Georg Brenneis, Claudia P ArangoAbstract:Background Sea spiders (Pycnogonida) are an abundant faunal element of the Southern Ocean (SO). Several recent phylogeographical studies focused on the remarkably diverse SO pycnogonid fauna, resulting in the identification of new species in previously ill-defined species complexes, insights into their genetic population substructures, and hypotheses on glacial refugia and recolonization events after the last ice age. However, knowledge on the life history of many SO pycnogonids is fragmentary, and early ontogenetic stages often remain poorly documented. This impedes assessing the impact of different developmental pathways on pycnogonid dispersal and distributions and also hinders pycnogonid-wide comparison of developmental features from a phylogenetic-evolutionary angle. Results Using scanning electron microscopy (SEM) and fluorescent nuclear staining, we studied embryonic stages and postembryonic instars of three SO representatives of the taxon Pallenopsidae ( Pallenopsis villosa , P. hodgsoni , P. vanhoeffeni ), the development of which being largely unknown. The eggs are large and yolk-rich, and the hatching stage is an advanced lecithotrophic instar that stays attached to the father for additional molts. The first free-living instar is deduced to possess at least three functional walking leg pairs. Despite gross morphological similarities between the congeners, each instar can be reliably assigned to a species based on body size, shape of ocular tubercle and proboscis, structure of the attachment gland processes, and seta patterns on cheliphore and walking legs. Conclusions We encourage combination of SEM with fluorescent markers in developmental studies on ethanol-preserved and/or long term-stored pycnogonid material, as this reveals internal differentiation processes in addition to external morphology. Using this approach, we describe the first known cases of pallenopsid development with epimorphic tendencies, which stand in contrast to the small hatching larvae in other Pallenopsidae. Evaluation against current phylogenetic hypotheses indicates multiple gains of epimorphic development within Pycnogonida. Further, we suggest that the type of development may impact pycnogonid distribution ranges, since free-living larvae potentially have a better dispersal capability than lecithotrophic attaching instars. Finally, we discuss the bearing of pycnogonid cheliphore development on the evolution of the raptorial first limb pair in Chelicerata and support a multi-articled adult limb as the plesiomorphic state of the chelicerate crown group, arising ontogenetically via postembryonic segmentation of a three-articled embryonic limb.
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comparison of ventral organ development across Pycnogonida arthropoda chelicerata provides evidence for a plesiomorphic mode of late neurogenesis in sea spiders and myriapods
BMC Evolutionary Biology, 2018Co-Authors: Georg Brenneis, Gerhard Scholtz, Barbara S. BeltzAbstract:Comparative studies of neuroanatomy and neurodevelopment provide valuable information for phylogenetic inference. Beyond that, they reveal transformations of neuroanatomical structures during animal evolution and modifications in the developmental processes that have shaped these structures. In the extremely diverse Arthropoda, such comparative studies contribute with ever-increasing structural resolution and taxon coverage to our understanding of nervous system evolution. However, at the neurodevelopmental level, in-depth data remain still largely confined to comparably few laboratory model organisms. Therefore, we studied postembryonic neurogenesis in six species of the bizarre Pycnogonida (sea spiders), which – as the likely sister group of all remaining chelicerates – promise to illuminate neurodevelopmental changes in the chelicerate lineage. We performed in vivo cell proliferation experiments with the thymidine analogs 5-bromo-2′-deoxyuridine and 5-ethynl-2′-deoxyuridine coupled to fluorescent histochemical staining and immunolabeling, in order to compare ventral nerve cord anatomy and to localize and characterize centers of postembryonic neurogenesis. We report interspecific differences in the architecture of the subesophageal ganglion (SEG) and show the presence of segmental “ventral organs” (VOs) that act as centers of neural cell production during gangliogenesis. These VOs are either incorporated into the ganglionic soma cortex or found on the external ganglion surface. Despite this difference, several shared features support homology of the two VO types, including (1) a specific arrangement of the cells around a small central cavity, (2) the presence of asymmetrically dividing neural stem cell-like precursors, (3) the migration of newborn cells along corresponding pathways into the cortex, and (4) the same VO origin and formation earlier in development. Evaluation of our findings relative to current hypotheses on pycnogonid phylogeny resolves a bipartite SEG and internal VOs as plesiomorphic conditions in pycnogonids. Although chelicerate taxa other than Pycnogonida lack comparable VOs, they are a characteristic feature of myriapod gangliogenesis. Accordingly, we propose internal VOs with neurogenic function to be part of the ground pattern of Arthropoda. Further, our findings illustrate the importance of dense sampling in old arthropod lineages – even if as gross-anatomically uniform as Pycnogonida – in order to reliably differentiate plesiomorphic from apomorphic neurodevelopmental characteristics prior to outgroup comparison.
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Comparison of ventral organ development across Pycnogonida (Arthropoda, Chelicerata) provides evidence for a plesiomorphic mode of late neurogenesis in sea spiders and myriapods
BMC, 2018Co-Authors: Georg Brenneis, Gerhard Scholtz, Barbara S. BeltzAbstract:Abstract Background Comparative studies of neuroanatomy and neurodevelopment provide valuable information for phylogenetic inference. Beyond that, they reveal transformations of neuroanatomical structures during animal evolution and modifications in the developmental processes that have shaped these structures. In the extremely diverse Arthropoda, such comparative studies contribute with ever-increasing structural resolution and taxon coverage to our understanding of nervous system evolution. However, at the neurodevelopmental level, in-depth data remain still largely confined to comparably few laboratory model organisms. Therefore, we studied postembryonic neurogenesis in six species of the bizarre Pycnogonida (sea spiders), which – as the likely sister group of all remaining chelicerates – promise to illuminate neurodevelopmental changes in the chelicerate lineage. Results We performed in vivo cell proliferation experiments with the thymidine analogs 5-bromo-2′-deoxyuridine and 5-ethynl-2′-deoxyuridine coupled to fluorescent histochemical staining and immunolabeling, in order to compare ventral nerve cord anatomy and to localize and characterize centers of postembryonic neurogenesis. We report interspecific differences in the architecture of the subesophageal ganglion (SEG) and show the presence of segmental “ventral organs” (VOs) that act as centers of neural cell production during gangliogenesis. These VOs are either incorporated into the ganglionic soma cortex or found on the external ganglion surface. Despite this difference, several shared features support homology of the two VO types, including (1) a specific arrangement of the cells around a small central cavity, (2) the presence of asymmetrically dividing neural stem cell-like precursors, (3) the migration of newborn cells along corresponding pathways into the cortex, and (4) the same VO origin and formation earlier in development. Conclusions Evaluation of our findings relative to current hypotheses on pycnogonid phylogeny resolves a bipartite SEG and internal VOs as plesiomorphic conditions in pycnogonids. Although chelicerate taxa other than Pycnogonida lack comparable VOs, they are a characteristic feature of myriapod gangliogenesis. Accordingly, we propose internal VOs with neurogenic function to be part of the ground pattern of Arthropoda. Further, our findings illustrate the importance of dense sampling in old arthropod lineages – even if as gross-anatomically uniform as Pycnogonida – in order to reliably differentiate plesiomorphic from apomorphic neurodevelopmental characteristics prior to outgroup comparison
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The ‘ventral organs’ of Pycnogonida (Arthropoda) are neurogenic niches of late embryonic and post-embryonic nervous system development. PLoS One. 2014;9(4):e95435. doi
2016Co-Authors: Georg Brenneis, Gerhard ScholtzAbstract:Early neurogenesis in arthropods has been in the focus of numerous studies, its cellular basis, spatio-temporal dynamics and underlying genetic network being by now comparably well characterized for representatives of chelicerates, myriapods, hexapods and crustaceans. By contrast, neurogenesis during late embryonic and/or post-embryonic development has received less attention, especially in myriapods and chelicerates. Here, we apply (i) immunolabeling, (ii) histology and (iii) scanning electron microscopy to study post-embryonic ventral nerve cord development in Pseudopallene sp., a representative of the sea spiders (Pycnogonida), the presumable sister group of the remaining chelicerates. During early post-embryonic development, large neural stem cells give rise to additional ganglion cell material in segmentally paired invaginations in the ventral ectoderm. These ectodermal cell regions – traditionally designated as ‘ventral organs ’ – detach from the surface into the interior and persist as apical cell clusters on the ventral ganglion side. Each cluster is a post-embryonic neurogenic niche that features a tiny central cavity and initially still houses larger neural stem cells. The cluster stays connected to the underlying ganglionic somata cortex via an anterior and a posterior cell stream. Cell proliferation remains restricted to the cluster and streams, and migration of newly produced cells along the streams seems to account for increasing ganglion cell numbers in the cortex. The pycnogonid cluster-stream-systems show striking similarities to the life-long neurogenic system of decapod crustaceans, and due to their close vicinity to glomerulus-like neuropils, we conside
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serotonin immunoreactivity in the ventral nerve cord of Pycnogonida support for individually identifiable neurons as ancestral feature of the arthropod nervous system
BMC Evolutionary Biology, 2015Co-Authors: Georg Brenneis, Gerhard ScholtzAbstract:The arthropod ventral nerve cord features a comparably low number of serotonin-immunoreactive neurons, occurring in segmentally repeated arrays. In different crustaceans and hexapods, these neurons have been individually identified and even inter-specifically homologized, based on their soma positions and neurite morphologies. Stereotypic sets of serotonin-immunoreactive neurons are also present in myriapods, whereas in the investigated chelicerates segmental neuron clusters with higher and variable cell numbers have been reported. This led to the suggestion that individually identifiable serotonin-immunoreactive neurons are an apomorphic feature of the Mandibulata. To test the validity of this neurophylogenetic hypothesis, we studied serotonin-immunoreactivity in three species of Pycnogonida (sea spiders). This group of marine arthropods is nowadays most plausibly resolved as sister group to all other extant chelicerates, rendering its investigation crucial for a reliable reconstruction of arthropod nervous system evolution. In all three investigated pycnogonids, the ventral walking leg ganglia contain different types of serotonin-immunoreactive neurons, the somata of which occurring mostly singly or in pairs within the ganglionic cortex. Several of these neurons are readily and consistently identifiable due to their stereotypic soma position and characteristic neurite morphology. They can be clearly homologized across different ganglia and different specimens as well as across the three species. Based on these homologous neurons, we reconstruct for their last common ancestor (presumably the pycnogonid stem species) a minimal repertoire of at least seven identified serotonin-immunoreactive neurons per hemiganglion. Beyond that, each studied species features specific pattern variations, which include also some neurons that were not reliably labeled in all specimens. Our results unequivocally demonstrate the presence of individually identifiable serotonin-immunoreactive neurons in the pycnogonid ventral nerve cord. Accordingly, the validity of this neuroanatomical feature as apomorphy of Mandibulata is questioned and we suggest it to be ancestral for arthropods instead. The pronounced disparities between the segmental pattern in pycnogonids and the one of studied euchelicerates call for denser sampling within the latter taxon. By contrast, overall similarities between the pycnogonid and myriapod patterns may be indicative of single cell homologies in these two taxa. This notion awaits further substantiation from future studies.
Roland R Melzer - One of the best experts on this subject based on the ideXlab platform.
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Feeding ecology in sea spiders (Arthropoda: Pycnogonida): what do we know?
Frontiers in Zoology, 2018Co-Authors: Lars Dietz, Tobias Lehmann, Jana S. Dömel, Florian Leese, Roland R MelzerAbstract:Sea spiders (Pycnogonida) are a widespread and phylogenetically important group of marine arthropods. However, their biology remains understudied, and detailed information about their feeding ecology is difficult to find. Observations on pycnogonid feeding are scattered in the literature, often in older sources written in various languages, and have never been comprehensively summarized. Here we provide an overview of all information on feeding in pycnogonids that we have been able to find and review what is known on feeding specializations and preferences in the various pycnogonid taxa. We deduce general findings where possible and outline future steps necessary to gain a better understanding of the feeding ecology of one of the world’s most bizarre animal taxa.
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Sense organs in Pycnogonida: A review
Acta Zoologica, 2017Co-Authors: Tobias Lehmann, Martin Heß, Roland R MelzerAbstract:The Pycnogonida or sea spiders are exclusively marine invertebrates, numbering about 1,300 described species worldwide. Given their remarkable position in phylogeny as basal chelicerates or even basal euarthropods, the structure of their sense organs can reveal important characters, which—in a comparative framework—provide arguments to phylogenetic discussions and help to develop scenarios of evolutionary transformations. This review summarizes current knowledge and presents new original data on the sense organs in pycnogonids, that is, the eyes, the lateral sense organs and the ciliary or sensillar sense organs. Except for the eyes, there are not many detailed studies available. The ultrastructure of the R-cells of the four eyes located on the ocular tubercle is described as “pseudoinverted”. The eyes are innervated to two visual neuropils located in the protocerebrum. The features of the lateral sense organ, also located on the ocular tubercle, are hitherto not conclusively resolved, a chemo- or thermoreceptive function is suggested. Finally, an overview of the various ciliary or sensillar sense organs distributed all over the body is given and the fine structure of branched setae is shown for the first time. The morphology of the sense organs of pycnogonids is compared with that of other arthropod taxa and assessed against the background of current theories of arthropod evolution.
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scientific note a deep water pycnogonid close to the beach colossendeis macerrima hoek 1881 spotted at 18 m in the chilean fjords chelicerata Pycnogonida colossendeidae
Spixiana, 2013Co-Authors: Gunter Forsterra, Roland R Melzer, Vreni Haussermann, Andrea WeisAbstract:Pycnogonida of the family Colossendeidae are in general deep sea inhabitants only exceptionally reported from depths less than 100 m. A face to face encounter with a Colossendeis during a scuba dive is therefore a singular experience. In the framework of the expeditions organized by the Huinay Scientific Field Station to create an inventory of Southern Chilean benthic communities and species (e. g. Haussermann & Forsterra 2009), a specimen of Colossendeis macerrima (ZSM collection number ZSMA20130110) was spotted at a depth of only 18.3 m on a rocky slope at Canal Farquhar (-48.52 S, -74.24 W) during the “HF13 – Puerto Eden” expedition to the Central Patagonian Zone. C. macerrima has a recorded range of depth between 121 and 4000 m, and in the Chilean fjord region this species was previously found at approx. 500 m (summarized in Weis & Melzer 2012). Thus, this is the only record from the upper infralitoral and euphotic zone. Earlier records of deep water species from various benthic marine groups in the upper part of the water column have been suggested to indicate deep water emergence, a special feature of the Chilean fjords (Forsterra & Haussermann 2003).
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wiring a periscope ocelli retinula axons visual neuropils and the ancestrality of sea spiders
PLOS ONE, 2012Co-Authors: Tobias Lehmann, Martin Hes, Roland R MelzerAbstract:The Pycnogonida or sea spiders are cryptic, eight-legged arthropods with four median ocelli in a ‘periscope’ or eye tubercle. In older attempts at reconstructing phylogeny they were Arthropoda incertae sedis, but recent molecular trees placed them as the sister group either to all other euchelicerates or even to all euarthropods. Thus, pycnogonids are among the oldest extant arthropods and hold a key position for the understanding of arthropod evolution. This has stimulated studies of new sets of characters conductive to cladistic analyses, e.g. of the chelifores and of the hox gene expression pattern. In contrast knowledge of the architecture of the visual system is cursory. A few studies have analysed the ocelli and the uncommon “pseudoinverted” retinula cells. Moreover, analyses of visual neuropils are still at the stage of Hanstrom's early comprehensive works. We have therefore used various techniques to analyse the visual fibre pathways and the structure of their interrelated neuropils in several species. We found that pycnogonid ocelli are innervated to first and second visual neuropils in close vicinity to an unpaired midline neuropil, i.e. possibly the arcuate body, in a way very similar to ancestral euarthropods like Euperipatoides rowelli (Onychophora) and Limulus polyphemus (Xiphosura). This supports the ancestrality of pycnogonids and sheds light on what eyes in the pycnogonid ground plan might have ‘looked’ like. Recently it was suggested that arthropod eyes originated from simple ocelli similar to larval eyes. Hence, pycnogonid eyes would be one of the early offshoots among the wealth of more sophisticated arthropod eyes.
Tobias Lehmann - One of the best experts on this subject based on the ideXlab platform.
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Feeding ecology in sea spiders (Arthropoda: Pycnogonida): what do we know?
Frontiers in Zoology, 2018Co-Authors: Lars Dietz, Tobias Lehmann, Jana S. Dömel, Florian Leese, Roland R MelzerAbstract:Sea spiders (Pycnogonida) are a widespread and phylogenetically important group of marine arthropods. However, their biology remains understudied, and detailed information about their feeding ecology is difficult to find. Observations on pycnogonid feeding are scattered in the literature, often in older sources written in various languages, and have never been comprehensively summarized. Here we provide an overview of all information on feeding in pycnogonids that we have been able to find and review what is known on feeding specializations and preferences in the various pycnogonid taxa. We deduce general findings where possible and outline future steps necessary to gain a better understanding of the feeding ecology of one of the world’s most bizarre animal taxa.
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Sense organs in Pycnogonida: A review
Acta Zoologica, 2017Co-Authors: Tobias Lehmann, Martin Heß, Roland R MelzerAbstract:The Pycnogonida or sea spiders are exclusively marine invertebrates, numbering about 1,300 described species worldwide. Given their remarkable position in phylogeny as basal chelicerates or even basal euarthropods, the structure of their sense organs can reveal important characters, which—in a comparative framework—provide arguments to phylogenetic discussions and help to develop scenarios of evolutionary transformations. This review summarizes current knowledge and presents new original data on the sense organs in pycnogonids, that is, the eyes, the lateral sense organs and the ciliary or sensillar sense organs. Except for the eyes, there are not many detailed studies available. The ultrastructure of the R-cells of the four eyes located on the ocular tubercle is described as “pseudoinverted”. The eyes are innervated to two visual neuropils located in the protocerebrum. The features of the lateral sense organ, also located on the ocular tubercle, are hitherto not conclusively resolved, a chemo- or thermoreceptive function is suggested. Finally, an overview of the various ciliary or sensillar sense organs distributed all over the body is given and the fine structure of branched setae is shown for the first time. The morphology of the sense organs of pycnogonids is compared with that of other arthropod taxa and assessed against the background of current theories of arthropod evolution.
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wiring a periscope ocelli retinula axons visual neuropils and the ancestrality of sea spiders
PLOS ONE, 2012Co-Authors: Tobias Lehmann, Martin Hes, Roland R MelzerAbstract:The Pycnogonida or sea spiders are cryptic, eight-legged arthropods with four median ocelli in a ‘periscope’ or eye tubercle. In older attempts at reconstructing phylogeny they were Arthropoda incertae sedis, but recent molecular trees placed them as the sister group either to all other euchelicerates or even to all euarthropods. Thus, pycnogonids are among the oldest extant arthropods and hold a key position for the understanding of arthropod evolution. This has stimulated studies of new sets of characters conductive to cladistic analyses, e.g. of the chelifores and of the hox gene expression pattern. In contrast knowledge of the architecture of the visual system is cursory. A few studies have analysed the ocelli and the uncommon “pseudoinverted” retinula cells. Moreover, analyses of visual neuropils are still at the stage of Hanstrom's early comprehensive works. We have therefore used various techniques to analyse the visual fibre pathways and the structure of their interrelated neuropils in several species. We found that pycnogonid ocelli are innervated to first and second visual neuropils in close vicinity to an unpaired midline neuropil, i.e. possibly the arcuate body, in a way very similar to ancestral euarthropods like Euperipatoides rowelli (Onychophora) and Limulus polyphemus (Xiphosura). This supports the ancestrality of pycnogonids and sheds light on what eyes in the pycnogonid ground plan might have ‘looked’ like. Recently it was suggested that arthropod eyes originated from simple ocelli similar to larval eyes. Hence, pycnogonid eyes would be one of the early offshoots among the wealth of more sophisticated arthropod eyes.
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Wiring a Periscope – Ocelli, Retinula Axons, Visual Neuropils and the Ancestrality of Sea Spiders
2012Co-Authors: Tobias Lehmann, Martin Heß, R. MelzerAbstract:The Pycnogonida or sea spiders are cryptic, eight-legged arthropods with four median ocelli in a ‘periscope ’ or eye tubercle. In older attempts at reconstructing phylogeny they were Arthropoda incertae sedis, but recent molecular trees placed them as the sister group either to all other euchelicerates or even to all euarthropods. Thus, pycnogonids are among the oldest extant arthropods and hold a key position for the understanding of arthropod evolution. This has stimulated studies of new sets of characters conductive to cladistic analyses, e.g. of the chelifores and of the hox gene expression pattern. In contrast knowledge of the architecture of the visual system is cursory. A few studies have analysed the ocelli and the uncommon ‘‘pseudoinverted’ ’ retinula cells. Moreover, analyses of visual neuropils are still at the stage of Hanström’s early comprehensive works. We have therefore used various techniques to analyse the visual fibre pathways and the structure of their interrelated neuropils in several species. We found that pycnogonid ocelli are innervated to first and second visual neuropils in close vicinity to an unpaired midline neuropil, i.e. possibly the arcuate body, in a way very similar to ancestral euarthropods like Euperipatoides rowelli (Onychophora) and Limulus polyphemus (Xiphosura). This supports the ancestrality of pycnogonids and sheds light on what eyes in the pycnogonid ground plan might have ‘looked ’ like. Recently it was suggested that arthropod eyes originated from simple ocelli similar to larval eyes. Hence, pycnogonid eyes would be one o
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Wiring a Periscope – Ocelli, Retinula Axons, Visual Neuropils and the Ancestrality of Sea Spiders
2011Co-Authors: Tobias Lehmann, Martin Heß, R. MelzerAbstract:The Pycnogonida or sea spiders are cryptic, eight-legged arthropods with four median ocelli in a ‘periscope ’ or eye tubercle. In older attempts at reconstructing phylogeny they were Arthropoda incertae sedis, but recent molecular trees placed them as the sister group either to all other euchelicerates or even to all euarthropods. Thus, pycnogonids are among the oldest extant arthropods and hold a key position for the understanding of arthropod evolution. This has stimulated studies of new sets of characters conductive to cladistic analyses, e.g. of the chelifores and of the hox gene expression pattern. In contrast knowledge of the architecture of the visual system is cursory. A few studies have analysed the ocelli and the uncommon ‘‘pseudoinverted’ ’ retinula cells. Moreover, analyses of visual neuropils are still at the stage of Hanström’s early comprehensive works. We have therefore used various techniques to analyse the visual fibre pathways and the structure of their interrelated neuropils in several species. We found that pycnogonid ocelli are innervated to first and second visual neuropils in close vicinity to an unpaired midline neuropil, i.e. possibly the arcuate body, in a way very similar to ancestral euarthropods like Euperipatoides rowelli (Onychophora) and Limulus polyphemus (Xiphosura). This supports the ancestrality of pycnogonids and sheds light on what eyes in the pycnogonid ground plan might have ‘looked ’ like. Recently it was suggested that arthropod eyes originated from simple ocelli similar to larval eyes. Hence, pycnogonid eyes would be one of the early offshoots among the wealth of more sophisticated arthropod eyes
Claudia P Arango - One of the best experts on this subject based on the ideXlab platform.
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First description of epimorphic development in Antarctic Pallenopsidae (Arthropoda, Pycnogonida) with insights into the evolution of the four-articled sea spider cheliphore
Zoological Letters, 2019Co-Authors: Georg Brenneis, Claudia P ArangoAbstract:Background Sea spiders (Pycnogonida) are an abundant faunal element of the Southern Ocean (SO). Several recent phylogeographical studies focused on the remarkably diverse SO pycnogonid fauna, resulting in the identification of new species in previously ill-defined species complexes, insights into their genetic population substructures, and hypotheses on glacial refugia and recolonization events after the last ice age. However, knowledge on the life history of many SO pycnogonids is fragmentary, and early ontogenetic stages often remain poorly documented. This impedes assessing the impact of different developmental pathways on pycnogonid dispersal and distributions and also hinders pycnogonid-wide comparison of developmental features from a phylogenetic-evolutionary angle. Results Using scanning electron microscopy (SEM) and fluorescent nuclear staining, we studied embryonic stages and postembryonic instars of three SO representatives of the taxon Pallenopsidae ( Pallenopsis villosa , P. hodgsoni , P. vanhoeffeni ), the development of which being largely unknown. The eggs are large and yolk-rich, and the hatching stage is an advanced lecithotrophic instar that stays attached to the father for additional molts. The first free-living instar is deduced to possess at least three functional walking leg pairs. Despite gross morphological similarities between the congeners, each instar can be reliably assigned to a species based on body size, shape of ocular tubercle and proboscis, structure of the attachment gland processes, and seta patterns on cheliphore and walking legs. Conclusions We encourage combination of SEM with fluorescent markers in developmental studies on ethanol-preserved and/or long term-stored pycnogonid material, as this reveals internal differentiation processes in addition to external morphology. Using this approach, we describe the first known cases of pallenopsid development with epimorphic tendencies, which stand in contrast to the small hatching larvae in other Pallenopsidae. Evaluation against current phylogenetic hypotheses indicates multiple gains of epimorphic development within Pycnogonida. Further, we suggest that the type of development may impact pycnogonid distribution ranges, since free-living larvae potentially have a better dispersal capability than lecithotrophic attaching instars. Finally, we discuss the bearing of pycnogonid cheliphore development on the evolution of the raptorial first limb pair in Chelicerata and support a multi-articled adult limb as the plesiomorphic state of the chelicerate crown group, arising ontogenetically via postembryonic segmentation of a three-articled embryonic limb.
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feeding biology of carnivore and detritivore mediterranean pycnogonids
Journal of the Marine Biological Association of the United Kingdom, 2013Co-Authors: Anna Solermembrives, Claudia P Arango, Montserrat Cuadrado, Tomas MunillaAbstract:The digestive system of sea spiders (Pycnogonida) presents peculiarities that have not been discussed in the context of their ecology or feeding behaviour. We investigated the digestive system of two Mediterranean species, a carnivorous species Ammothella longipes and a detritivorous Endeis spinosa , with special focus on its correlation with behavioural feeding habits. The midgut and hindgut sections did not present significant differences between the two species, but major differences were observed in the foregut, reflecting concordance to their diet and their feeding behaviour. Jaws, setose lips, the structure of the pharyngeal filter and musculature of the proboscis are the main differential elements when comparing feeding habits of A. longipes and E. spinosa . These elements are responsible for the reduction of the food pulp down to subcellular size. The digestion process observed in the species studied agrees with that observed in other pycnogonid lineages, but differs from most marine arthropods mainly because of the absence of midgut gland cells and the presence of a unique multifunctional type of midgut epithelial cell. Epithelial digestive cells are present in a small ‘resting’ form during starvation periods. During digestion, secretion granules possibly containing zymogen move to their apical border to be secreted to the midgut lumen, secondary lysosomes are formed and intracellular digestion occurs within them. Residual bodies are formed within the epithelial cell and released to the midgut lumen to be transported towards the hindgut. The characteristics of the digestive process of the pycnogonids studied seem to reflect a plesiomorphic state in arthropods.
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oxygen hypothesis of polar gigantism not supported by performance of antarctic pycnogonids in hypoxia
Proceedings of The Royal Society B: Biological Sciences, 2009Co-Authors: Arthur H Woods, Claudia P Arango, Amy L Moran, Lindy Mullen, Chris ShieldsAbstract:Compared to temperate and tropical relatives, some high-latitude marine species are large-bodied, a phenomenon known as polar gigantism. A leading hypothesis on the physiological basis of gigantism posits that, in polar water, high oxygen availability coupled to low metabolic rates relieves constraints on oxygen transport and allows the evolution of large body size. Here, we test the oxygen hypothesis using Antarctic pycnogonids, which have been evolving in very cold conditions (−1.8–0°C) for several million years and contain spectacular examples of gigantism. Pycnogonids from 12 species, spanning three orders of magnitude in body mass, were collected from McMurdo Sound, Antarctica. Individual sea spiders were forced into activity and their performance was measured at different experimental levels of dissolved oxygen (DO). The oxygen hypothesis predicts that, all else being equal, large pycnogonids should perform disproportionately poorly in hypoxia, an outcome that would appear as a statistically significant interaction between body size and oxygen level. In fact, although we found large effects of DO on performance, and substantial interspecific variability in oxygen sensitivity, there was no evidence for size×DO interactions. These data do not support the oxygen hypothesis of Antarctic pycnogonid gigantism and suggest that explanations must be sought in other ecological or evolutionary processes.
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microscopic anatomy of Pycnogonida ii digestive system iii excretory system
Journal of Morphology, 2007Co-Authors: W H Fahrenbach, Claudia P ArangoAbstract:The digestive system of several species of sea spiders (Pycnogonida, Arthropoda) was studied by electron microscopy. It is composed of the foregut inside a long proboscis, a midgut and a hindgut. Lips near the three jaws at the tip of the proboscis receive several hundred ductules originating from salivary glands. These previously undetected glands open on the lips, a fluted, projecting ridge at the external hinge line of the jaws, i.e., to the outside of the mouth. This disposition suggests affinities to the chelicerate line. The trigonal esophagus within the proboscis contains a complex, setose filter device, operated by dedicated muscles, that serves to reduce ingested food to subcellular dimensions. The midgut has diverticula into the bases of all legs. Its cells differentiate from the basal layer and contain a bewildering array of secretion droplets, lysosomes and phagosomes. In the absence of a hepatopancreas, the midgut serves both digestive and absorptive functions. The cuticle-lined hindgut lies in the highly reduced, peg-like abdomen. Traditionally, pycnogonids have been claimed to have no excretory organ at all. Such a structure, however, has been located in at least one ammotheid, Nymphopsis spinosissima, in which a simple, but standard, excretory gland has been found in the scape of the chelifore. It consists of an end sac, a straight proximal tubule, a short distal tubule, and a raised nephropore. The end sac is a thin-walled and polygonal chamber, about 150 μm in cross section, suspended in the hemocoel of the appendage, its edges radially tethered to the cuticle at more than half a dozen locations. This wall consists of a filtration basement membrane, 1–4 μm thick, facing the hemocoel, and internally of a continuous carpet of podocytes and their pedicels. The podocytes, measuring maximally 10 by 15 μm, have complex contents, of which a labyrinthine system of connected intracellular channels stands out. These coated cisternae open into a central vacuole that often rivals the nucleus in size. The design of the organ closely approximates that of the primitive crustacean Hutchinsoniella macracantha. J. Morphol., 2007. © 2007 Wiley-Liss, Inc.
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phylogeny of the sea spiders arthropoda Pycnogonida based on direct optimization of six loci and morphology
Cladistics, 2007Co-Authors: Claudia P ArangoAbstract:Higher-level phylogenetics of Pycnogonida has been discussed for many decades but scarcely studied from a cladistic perspective. Traditional taxonomic classifications are yet to be tested and affinities among families and genera are not well understood. Pycnogonida includes more than 1300 species described, but no systematic revisions at any level are available. Previous attempts to propose a phylogeny of the sea spiders were limited in characters and taxon sampling, therefore not allowing a robust test of relationships among lineages. Herein, we present the first comprehensive phylogenetic analysis of the Pycnogonida based on a total evidence approach and Direct Optimization. Sixty-three pycnogonid species representing all families including fossil taxa were included. For most of the extant taxa more than 6 kb of nuclear and mitochondrial DNA and 78 morphological characters were scored. The most parsimonious hypotheses obtained in equally weighted total evidence analyses show the two most diverse families Ammotheidae and Callipallenidae to be non-monophyletic. Austrodecidae + Colossendeidae + Pycnogonidae are in the basal most clade, these are morphologically diverse groups of species mostly found in cold waters. The raising of the family Pallenopsidae is supported, while Eurycyde and Ascorhynchus are definitely separated from Ammotheidae. The four fossil taxa are grouped within living Pycnogonida, instead of being an early derived clade. This phylogeny represents a solid framework to work towards the understanding of pycnogonid systematics, providing a data set and a testable hypothesis that indicate those clades that need severe testing, especially some of the deep nodes of the pycnogonid tree and the relationships of ammotheid and callipallenid forms. The inclusion of more rare taxa and additional sources of evidence are necessary for a phylogenetic classification of the Pycnogonida. © The Willi Hennig Society 2006.
