Comparative morphology of statocysts in the Plathelminthes and the Xenoturbellida

Ehlers, Ulrich

doi:10.1007/978-94-011-2775-2_38

Cited by 14 publications

(12 citation statements)

References 7 publications

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“…(Ehlers 1985 ), and Xenoturbellida (with one single hitherto described species, Xenoturbella bocki ) are simple, aquatic, acoelomate worms that measure between 100 μm and 1 cm. Or is their development due to the fact that ctenophores are holopelagic, direct-developing organisms that put a premium on getting to a free-living feeding stage as quickly as possible?…”

Section: Open Questionsmentioning

confidence: 99%

Evolutionary Developmental Biology of Invertebrates 1

2015

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Section: Open Questionsmentioning

confidence: 99%

Evolutionary Developmental Biology of Invertebrates 1

2015

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“…The hypothesis stating that Xenoturbellida forms a sister taxon to Bilateria was proposed by Ehlers (1991) and Ehlers and Sopott-Ehlers (1997a). The very simple organisation of the nervous system in Xenoturbellida described above is quite compatible with a basal position in the bilaterian tree.…”

Section: Phylogenetic Considerationsmentioning

confidence: 99%

“…According to Franzen and Afzelius (1987), Rohde et al (1988), Raikova (1989) and Lundin (1998), the ultrastructure of the ciliary tips and the system of the epidermal ciliary rootlets in X. bocki is similar to that of the Acoela and the Nemertodermatida, indicating a close relationship with these groups of Plathelminthes. According to Ehlers (1991), Xenoturbella constitutes a sister taxon to Bilateria. Recent cladistic analysis of 18S rDNA and cytochrome c oxidase subunit I nucleotide data in X. bocki points to a position within the Lophotrochozoa, most likely closely related to the protobranch bivalves (Norén and Jondelius 1997).…”

Section: A Introductionmentioning

confidence: 99%

An immunocytochemical and ultrastructural study of the nervous and muscular systems of Xenoturbella westbladi (Bilateria inc. sed.)

et al. 2000

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The phylogenetic position of the Xenoturbellida is highly disputed. Are they primitive flatworms? Are they related to Deuterostomia? Do they form a sister taxon to other Bilateria? Are they bivalve molluscs? In order to provide more data for this discussion, a study of the nervous system of Xenoturbella westbladi and its relation to the musculature was performed, using 5-HT and FMRFamide immunocytochemistry, TRITC-conjugated phalloidin fluorescence for staining of F-actin filaments, confocal scanning laser microscopy and transmission electron microscopy. The nervous system comprises solely an intraepidermal net of nerve cells and processes. No ganglia or any other internal nervous structures could be detected. No evidence of 5-HT-or FMRFamide-immunoreactive innervation below the subepidermal membrane complex was obtained. The 5-HT and FMRFamide immunoreactivity occurs in separate sets of neurones. On the ultrastructural level, three types of neurones were observed: (1) the predominating "light" neurones, (2) the smaller "dark" neurones and (3) the bipolar sensory neurones bearing a single cilium with a long bipartite rootlet. Non-synaptic, paracrine, release sites are common and synapses are inconspicuous. In the layer of epidermal cells, close to the lateral furrow, F-actin filaments were observed. They reach from the basal membrane to the surface. The organisation of the nervous system appears very simple. Our results are compatible with the hypothesis of Xenoturbellida forming a sister taxon to Bilateria. No evidence was obtained for inclusion of X. westbladi in either the Mollusca or Plathelminthes.An immunocytochemical and ultrastructural study of the nervous and muscular systems of Xenoturbella westbladi (Bilateria inc. sed.)

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“…Fine-structural investigations of X. bocki have been done by Pedersen andPedersen (1986, 1988) on the subepidermal extracellular matrices and on the organization of the epidermis, by Franzén and Afzelius (1987) on the epidermal cilia and by Ehlers (1991) on the intraepidermal statocyst-like organ. The epidermal cilia with shelflike terminations of the axonemes resemble those of species of the Acoelomorpha (Plathelminthes) and revived O R I G I N A L A RT I C L E…”

Section: A Introductionmentioning

confidence: 99%

Ultrastructure of the subepidermal musculature of Xenoturbella bocki, the adelphotaxon of the Bilateria

Ehlers

Sopott‐Ehlers

1997

Zoomorphology

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Xenoturbella bocki is the only species of the high-ranked taxon Xenoturbellida. The species lives on marine mud bottoms at a depth of 20-120 m and moves extremely slowly by ciliary gliding. Nevertheless it possesses a well-developed body wall musculature with outer circular muscles, a prominent layer of inner longitudinal muscles and radial muscles that extend from the outer circular myocytes to the musculature surrounding the gastrodermis. The longitudinal myocytes are not compact cells, but form fascicles of fibrils running parallel to each other. Fine cytoplasmic cords connect the fibres of a cell to each other and with its nuclear region. The muscles are embedded within a sometimes expansive extracellular matrix (ECM) that lacks any fibrillar components. All muscle cells display conspicuous and numerous cytoplasmic extensions that are intermingled with each other. Tight coupling between adjacent cell membranes is not found, but zonula adhaerens-like junctions exist. Fibrils belonging to different myocytes, but also fibrils of the same cell, are coupled by such cytoplasmic extensions. Circular, radial and at least the peripheral longitudinal myocytes display cell-matrix connections with the internal lamina, a component of the subepidermal ECM. This internal lamina projects down into the centres of the fascicles with longitudinal muscle fibrils and forms extensive attachment zones with the muscle cells, reminiscent of focal contacts. For the ingestion of food, X. bocki opens the simple mouth pore and protrudes the aciliated gastrodermis. The body wall musculature is responsible for this protrusion and also for the withdrawal of the gastrodermis. In the past, possible phylogenetic kinships with the Acoelomorpha (Plathelminthes) or the Enteropneusta and Holothuroidea were discussed, but, on the basis of all information available, X. bocki is hypothesized to be the sister taxon of the Bilateria.& b d y :

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Comparative morphology of statocysts in the Plathelminthes and the Xenoturbellida

Cited by 14 publications

References 7 publications

Evolutionary Developmental Biology of Invertebrates 1

Evolutionary Developmental Biology of Invertebrates 1

An immunocytochemical and ultrastructural study of the nervous and muscular systems of Xenoturbella westbladi (Bilateria inc. sed.)

Ultrastructure of the subepidermal musculature of Xenoturbella bocki, the adelphotaxon of the Bilateria

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