1,721,016 research outputs found
Temporal plasticity in annelid development--ontogeny of Phyllodoce groenlandica (Phyllodocidae, Annelida) reveals heterochronous patterns
No full textThe variety of annelid larval types and developmental modes reflects the high diversity and variability within these lophotrochozoans. However, our knowledge of pattern formation and tissue development in annelids and allies is scarce. In order to gain more data concerning neurogenesis and myogenesis in annelid trochophores, we analyzed different larval stages of Phyllodoce groenlandica using immunohistochemical staining techniques and subsequent confocal laser scanning microscopy (clsm). Focusing on pre-metamorphic stages, we reconstruct the process of tissue and body formation within planktonic polychaetous trochophore larvae. Our investigations revealed detailed knowledge of general developmental modes in Annelida and exhibit ontogenetic heterochrony of tissue development between two closely related annelid species. As such, P. groenlandica shows a delayed onset of nervous system development when compared with P. maculata. In contrast to the latter species, we were not able to detect the posterior sensory organ in larval P. groenlandica. We draw conclusions concerning general development of annelid trochophores and provide data showing new insights into the plasticity of body plans in Annelida
Loss of complexity from larval towards adult nervous systems in Chaetopteridae (Chaetopteriformia, Annelida) unveils evolutionary patterns in Annelida
No full textAbstract Chaetopteridae — the parchment worms — comprise a group of early branching annelids with a scarcely investigated neuroanatomy and neurogenesis. Due to their phylogenetic position in the annelid tree, studying them is nevertheless inevitable for our understanding of character evolution in segmented worms. Therefore, we investigated several adult und larval chaetopterids using a broad set of morphological methods — including serial azan-stained histological sections as well as ultrastructural and immunohistochemical approaches. Our investigations shows that the chaetopterid nervous system consists of a medullary and intraepidermal anterior brain without major commissures and only one neuron type. Nuchal organs and complex cup-shaped eyes are absent in adult specimens. The developmental investigations reveal an antero-posterior origin of the larval nervous system, which is in line with previous investigations and supports this character as being plesiomorphic at least for Annelida. Furthermore, the reduction of neuronal complexity during ontogenesis hints towards the necessity of developmental examinations to understand the evolutionary scenarios behind nervous system diversity not only in annelid taxa. Our detailed investigations will help to deepen our knowledge in terms of annelid character evolution and will build up a basis for further detailed examinations dealing with this fascinating group of segmented worms.Deutsche ForschungsgemeinschaftGeorg-August-Universität Göttingen 50110000338
Development and structure of the anterior nervous system and sense organs in the holopelagic annelid Tomopteris spp. (Phyllodocida, Errantia)
No full textAbstract Tomopteridae are transparent, predatory Annelida inhabiting pelagic ocean zones. Despite being well-known for their fast metachronal swimming and species-specific bioluminescence, our knowledge of morphological adaptations in these fascinating holopelagic worms remains extremely limited. In particular, the evolutionary scenarios and adaptive changes related to the transition from putative benthic ancestors to recent free-swimming groups remain poorly investigated and understood. Therefore, we investigated different taxa and developmental stages within the holopelagic Tomopteridae. We used a comparative morphological approach, including a range of microscopic methods, in our investigations focused on the anterior nervous system and prominent sensory structures, such as nuchal organs and tentacular cirri, in early developmental and adult stages of four tomopterid species. Our data show that Tomopteridae undergo heterochronic, lecithotrophic development with early visibility of adult-like features, which is consistent with earlier investigations. Furthermore, our ultrastructural examinations of the tomopterid nuchal organ highlight the conservativism in the fine structure and development of this prominent polychaete chemosensory organ. Nevertheless, our data indicate ultrastructural differences, such as an extraordinary number of supporting cell types and a bipartite olfactory chamber, potentially related to their pelagic lifestyle. In contrast to previous assumptions, it is shown that the supporting structures in the cirrus-like appendages of the first chaetiger contain prominent intracellular skeletal elements rather than annelid chaetae. These findings highlight the need for further investigations to understand Annelida’s immense morphological diversity of organ systems. Furthermore, our data demonstrate the necessity of functional analyses to understand Annelida’s adaptive radiation of sensory and neuronal structures.DFGUniversität Osnabrück http://dx.doi.org/10.13039/50110001637
Immunohistochemical investigations of Myzostoma cirriferum and Mesomyzostoma cf. katoi (Myzostomida, Annelida) with implications for the evolution of the myzostomid body plan
No full textFrom two segments and beyond: Investigating the onset of regeneration in Syllis malaquini
No full textAbstract Annelids feature a diverse range of regenerative abilities, but complete whole‐body regeneration is less common, particularly in the context of the head and anterior body regeneration. This study provides a detailed morphological description of Syllis malaquini regenerative abilities. By replicating previous experiments and performing diverse surgical procedures, we explored the capacity of this species for whole‐body regeneration. We detailed the precise timing of regeneration of particular structures such as the eyes, proventricle, pharyngeal tooth, nuchal organs, and body pigmentation after amputation. Our high‐resolution scanning electron microscopy and confocal laser‐scanning microscopy images provide details of the blastema region, revealing that while anal opening remains in connection to the exterior environment, oral opening is formed “ de novo ” during blastema differentiation. Additionally, we performed amputations to isolate fragments consisting of one, two, and three segments from the intestinal trunk region. We found that S. malaquini requires at least two to three segments to successfully regenerate the whole body. In addition, we verified a variable capacity to regenerate depending upon the gut region, with structures of the foregut greatly impairing some steps of the regenerative process. Our work notably addresses the gap in knowledge concerning gut formation and its impact on regenerative capabilities. Ongoing research is crucial to unravel the role of gut tissue specificity and plasticity during regeneration in annelids, and particularly in syllids.Research Highlights The study reveals that the segmented worm Syllis malaquini achieves successful whole‐body regeneration with a minimum of two segments, and underscores the relevance of gut tissue specificity and plasticity during regeneration.Abstract Annelids feature a diverse range of regenerative abilities, but complete whole‐body regeneration is less common, particularly in the context of the head and anterior body regeneration. This study provides a detailed morphological description of Syllis malaquini regenerative abilities. By replicating previous experiments and performing diverse surgical procedures, we explored the capacity of this species for whole‐body regeneration. We detailed the precise timing of regeneration of particular structures such as the eyes, proventricle, pharyngeal tooth, nuchal organs, and body pigmentation after amputation. Our high‐resolution scanning electron microscopy and confocal laser‐scanning microscopy images provide details of the blastema region, revealing that while anal opening remains in connection to the exterior environment, oral opening is formed “ de novo ” during blastema differentiation. Additionally, we performed amputations to isolate fragments consisting of one, two, and three segments from the intestinal trunk region. We found that S. malaquini requires at least two to three segments to successfully regenerate the whole body. In addition, we verified a variable capacity to regenerate depending upon the gut region, with structures of the foregut greatly impairing some steps of the regenerative process. Our work notably addresses the gap in knowledge concerning gut formation and its impact on regenerative capabilities. Ongoing research is crucial to unravel the role of gut tissue specificity and plasticity during regeneration in annelids, and particularly in syllids.Research Highlights The study reveals that the segmented worm Syllis malaquini achieves successful whole‐body regeneration with a minimum of two segments, and underscores the relevance of gut tissue specificity and plasticity during regeneration
Palps across the tree - the neuronal innervation and development of sensory head appendages in Annelida
No full textPolychaetes inhabit a wide variety of habitats and show a great morphological diversity. In this context, a key morphological structure for adapting to their individual lifestyles and ecological niches are the prominent head appendages. In the last years more and more studies focused on the mainly sensory annelid head appendages - namely the antennae, palps, buccal lips and cirri - to unravel the evolutionary origin and phylogeny of Annelida. Unfortunately, comparable data for most of the polychaete families are lacking so far, especially when it comes to features of the larval anterior nervous system and the related innervation and potential homology of these head appendages. In this study, we therefore use an integrative morphological approach including immunohistochemistry and confocal laser scanning microscopy in combination with histological serial sections and 3D-visualizations. With special focus on the palp-like appendages, our data provides a closer look into the development of the larval anterior nervous system and the related sensory structures of three polychaete families representing major groups of the annelid tree of life. Hence, we investigate members of the palaeoannelid Magelonidae as well as basally-branching Amphinomidae, and the pleistoannelid Spionidae forming a taxon deeply nested within Sedentaria. Our comparative data of larval and adult neuronal features support the homology of feeding-palps across the annelid tree. Furthermore, our observations show that larval palps gradually transform into the adult ones while keeping a very similar neuronal innervation pattern. Solely for Amphinomidae a loss of larval palps during ontogenesis has to be assumed. Therefore, our investigations uncover important and so far unknown details in terms of structural homology across Annelida and provide important results necessary for our understanding of annelid evolution.Open-Access-Publikationsfonds 202
Myoanatomy of Myzostoma cirriferum (Annelida, Myzostomida): implications for the evolution of the myzostomid body plan
No full textStudies of rare genomic marker systems suggest that Myzostomida are a subgroup of Annelida and phylogenomic analyses indicate an early divergence of this taxon within annelids. However, adult myzostomids show a highly specialized body plan, which lacks typical annelid features, such as external body annulation, coelomic cavities with metanephridia, and segmental ganglia of the nervous system. The putative loss of these features might be due to the parasitic/symbiotic lifestyle of myzostomids associated with echinoderms. In contrast, the larval anatomy and adult locomotory system resemble those of annelids. To clarify whether the myoanatomy of myzostomids reflects their relationship to annelids, we analyzed the distribution of f-actin, a common component of muscle fibers, in specimens of Myzostoma cirriferum using phalloidin-rhodamine labeling in conjunction with confocal laser-scanning microscopy. Our data reveal that the musculature of the myzostomid body comprises an outer circular layer, an inner longitudinal layer, numerous dorsoventral muscles, and prominent muscles of the parapodial complex. These features correspond well with the common organization of the muscular system in Annelida. In contrast to other annelids, however, several elements of the muscular system in M. cirriferum, including the musculature of the body wall, and the parapodial flexor muscles, exhibit radial symmetry overlaying a bilateral body plan. These findings are in line with the annelid affinity of myzostomids and suggest that the apparent partial radial symmetry of M. cirriferum arose secondarily in this species. Based on our data, we provide a scenario on the rearrangements of muscle fibers that might have taken place in the lineage leading to this species
Description of a new syllid species as a model for evolutionary research of reproduction and regeneration in annelids
No full textThe anatomy and development of the nervous system in Magelonidae (Annelida) – insights into the evolution of the annelid brain
No full textAbstract Background The annelid anterior central nervous system is often described to consist of a dorsal prostomial brain, consisting of several commissures and connected to the ventral ganglionic nerve cord via circumesophageal connectives. In the light of current molecular phylogenies, our assumptions on the primary design of the nervous system in Annelida has to be reconsidered. For that purpose we provide a detailed investigation of the adult nervous system of Magelonidae – a putatively basally branching annelid family - and studied early stages of the development of the latter. Results Our comparative investigation using an integrative morphological approach shows that the nervous system of Magelonidae is located inside the epidermis. The brain is composed of an anterior compact neuropil and posteriorly encircles the prostomial coelomic cavities. From the brain two lateral medullary cords branch off which fuse caudally. Prominent brain structures such as nuchal organs, ganglia or mushroom bodies are absent and the entire nervous system is medullary. Our investigations also contradict previous investigations and present an updated view on established assumptions and descriptions. Conclusion The comprehensive dataset presented herein enables a detailed investigation of the magelonid anterior central nervous system for the first time. The data reveal that early in annelid evolution complexity of brains and anterior sensory structures rises. Polymorphic neurons in clusters and distinct brain parts, as well as lateral organs - all of which are not present in outgroup taxa and in the putative magelonid sister group Oweniidae - already evolved in Magelonidae. Commissures inside the brain, ganglia and nuchal organs, however, most likely evolved in the stem lineage of Amphinomidae + Sipuncula and Pleistoannelida (Errantia+ Sedentaria). The investigation demonstrates the necessity to continuously question established descriptions and interpretations of earlier publications and the need for transparent datasets. Our results also hint towards a stronger inclusion of larval morphology and developmental investigations in order to understand adult morphological features, not only in Annelida
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