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  • 1
    Electronic Resource
    Electronic Resource
    Electron microscopic studies of the digestive tract and absorption from the gut lumen of a feather star, oligometra serripinna (Echinodermata) (1984)
    Springer
    Zoomorphology 104 (1984), S. 252-259 
    Details
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The gut of a crinoid echinoderm is described for the first time by transmission electron microscopy. The gut comprises a short esophagus, a relatively long intestine and a short rectum. From the luminal side to the coelomic side, the layers of the gut wall are an inner epithelium, an epineural plexus (much reduced or absent in the intestine and rectum), haemal fluid, smooth muscles mixed with a hyponeural plexus, and a visceral peritoneum. The inner epithelium of the esophagus consists of numerous flagellated enterocytes and some mucous cells containing abundant mucous granules. The luminal surface of the esophagus, but not that of the other gut regions, is covered by a conspicuous cuticle. The inner epithelium of the intestine consists of some exocrine cells, presumably exporting digestive enzymes to the gut lumen, and numerous vesicular enterocytes that are flagellated and contain a few apical mucous granules. The inner epithelium of the rectum is made up entirely of vesicular enterocytes most of which lack a flagellum. The uptake of macromolecules from the gut lumen was demonstrated by feeding the feather stars food mixed with ferritin. By 4 h after feeding, ferritin was identified in presumed secondary lysosomes within the enterocytes of the esophagus and within the vesicular enterocytes of the intestine and rectum. The functional implications of the new fine structural results are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00312039
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  • 2
    Electronic Resource
    Electronic Resource
    Fine structure of the stalk of an isocrinid sea lily (Metacrinus rotundus) (Echinodermata, Crinoidea) (1985)
    Springer
    Zoomorphology 105 (1985), S. 39-50 
    Details
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Sea lilies of the order Isocrinida (Metacrinus rotundus) were dredged from Sagami Bay, Japan, and their stalks were studied by transmission electron microscopy. New contributions to stalk histology are: an exact description of the different cell types in the stereom spaces; a demonstration of the haemal channel; and the discovery of (1) coelomic nerves, (2) collateral stalk nerves and (3) nerve tracts running with the aboral extension of the axial organ. Within the stalk, there is no structure derived from the axial sinus (=axocoel), and the widely accepted homology between the crinoid stalk and the larval asteroid stalk is thus open to serious question. The stalk has collagenous ligaments of two main types (intercolumnal ligaments and peripheral through-going ligaments); however, there are no central through-going ligaments comparable to those in stalks of larval feather stars and of bourgueticrinid sea lilies. The absence of muscles or other cells specialized for contractility indicates that the stalk of isocrinid sea lilies cannot bend actively. The cirri, which project from the stalk of M. rotundus, contain no muscle cells; however, the epithelial cells lining the oral and aboral coeloms of each cirrus contain a presumed contractile apparatus that is a bundle of 5 nm cytoplasmic filaments oriented parallel to each other and to the long axis of the cirrus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00312072
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  • 3
    Electronic Resource
    Electronic Resource
    Fine structure of syzygial articulations before and after arm autotomy in florometra serratissima (Echinodermata: Crinoidea) (1981)
    Springer
    Zoomorphology 98 (1981), S. 169-183 
    Details
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary About 1 s after appropriate stimulation, arms of Florometra serratissima break at articulations called syzygies that are specialized for autotomy. The fine structure of unreacted and of newly broken syzygies is described. The unreacted syzygy includes (1) ligament fibers consisting of collagen fibrils interconnected by interfibrillar strands and (2) axons filled with presumed neurosecretory granules. The newly broken syzygy includes (1) ruptured ligament fibers consisting of swollen collagen fibrils associated with interfibrillar globules and (2) axons containing few presumed neurosecretory granules, some of which are fixed in the act of exocytosis; moreover, the calcareous skeleton adjacent to the broken syzygy is partly eroded. The observations before and after breaking suggest that the autotomy mechanism may comprise the following sequence of events: rapid neural transmission from stimulation site to syzygy triggers a massive exocytosis of granules from presumed neurosecretory axons; the released neurosecretions (which could include chelating agents, strong acids, proteolytic enzymes or enzyme activators) etch the skeleton and lower the tensile strength of the ligament fibers by weakening the collagen fibrils and/or the interfibrillar material; breakage of the ligament fibers, the major connective tissue of the articulation, is quickly followed by rupture of all the other tissues at the syzygy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310434
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  • 4
    Electronic Resource
    Electronic Resource
    The structure of the sea lilyCalamocrinus diomedae, with special reference to the articulations, skeletal microstructure, symbiotic bacteria, axial organs, and stalk tissues (Crinoida, Millericrinida) (1991)
    Springer
    Zoomorphology 110 (1991), S. 115-132 
    Details
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Calamocrinus diomedae was collected in deep water in the eastern Pacific. The skeleton and soft tissues were studied by light microscopy and by scanning and transmission electron microscopy. The skeleton of the arms and pinnules was unusual in lacking any galleried stereom; thus the ligaments as well as the muscles inserted on labyrinthic stereom. Therefore, the type of skeletal microstructure may not always be a sure guide to where the ligaments and muscles insert, and crinoid paleontologists should use caution when reconstructing soft parts from fossil skeletons. Contrary to the original species description, the skeleton of the theca apparently includes no infrabasal ossicles, andC. diomedae is monocyclic like other millericrinid sea lilies. Although many of the soft tissues resemble those of other crinoids, there are several exceptional features. The visceral mass within the theca includes not only a glandular axial organ typical of crinoids generally, but also what appears to be a second axial organ of the eleutherozoan type; dual axial organs have been seen before only in isocrinid sea lilies. The gut contents include partially digested crustacean prey, including some calanoid copepods. The soft tissues of the axial cord of the stalk comprise a haemal vessel, an aboral extension of the glandular axial organ, aboral coelomic extensions of the chambered organ, coelomic nerves, stalk nerves, an inconspicuous central through-going ligament, and aggregations of cells in each radial sector. Spherical bodies filled with rodshaped symbiotic bacteria are embedded in the soft connective tissues of the arms and pinnules. Possible chemosynthetic and bioluminescent roles for these bacteria are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01632868
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  • 5
    Electronic Resource
    Electronic Resource
    Haemal and coelomic circulatory systems in the arms and pinnules ofFlorometra serratissima (Echinodermata: Crinoidea) (1979)
    Springer
    Zoomorphology 94 (1979), S. 93-109 
    Details
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The haemal and coelomic circulatory systems in arms and pinnules of a stalkless crinoid are described by transmission electron microscopy, and the coelomic topography is revealed by scanning electron microscopy of corrosion casts and peritoneal surfaces. In addition, the route of the coelomic circulation in the living crinoid is shown by injection of carmine particles, and sites of peritoneal phagocytosis are demonstrated by injection of latex beads. The most important morphological findings are: the controversial hyponeural circulation is haemal and not coelomic; peritoneal ciliation is general and not limited to the cells of the ciliated pits; and occur smooth muscle cells occur below the peritoneum. Carmine particles injected into the central body coelom rapidly travel outward toward the arm and pinnule tips via the aboral canals; the particles return to the central body via the subtentacular canals. Latex beads injected intracoelomically are taken up by peritoneal cells throughout the subtentacular, genital and aboral canals. The possible functions of the haemal and coelomic circulatory systems of crinoids are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00994059
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  • 6
    Electronic Resource
    Electronic Resource
    Epidermal mucus and the reproduction of a crinoid echinoderm (1975)
    [s.l.] : Nature Publishing Group
    Nature 255 (1975), S. 223-224 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In both sexes the volume of the epidermal mucous cell population increases conspicuously in the weeks before spawn ing (Fig. 2). In the female (Fig. 20) this increase is about ten times as great as in the male (Fig. 2b). The volume of the mucous cell population decreases markedly around the time of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/255223a0
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  • 7
    Electronic Resource
    Electronic Resource
    Annual Cycle in the Size of the Gut of the Purple Sea Urchin, Strongylocentrotus purpuratus (Stimpson) (1965)
    [s.l.] : Nature Publishing Group
    Nature 205 (1965), S. 1238-1239 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Twenty urchins were collected monthly from a tide pool near Yankee Point, California (36 33' N., 121 57' W.). The gut, exclusive of the pharynx, was dissected from each urchin, washed free of its contents, drained of free water, and weighed. The gonads were also removed, drained, and weighed. Both ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/2051238a0
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  • 8
    Electronic Resource
    Electronic Resource
    ‘Lophenteropneust’ hypothesis refuted by collection and photos of new deep-sea hemichordates (2005)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 434 (2005), S. 374-376 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The deep ocean is home to a group of broad-collared hemichordates—the so-called ‘lophenteropneusts’—that have been photographed gliding on the sea floor but have not previously been collected. It has been claimed that these worms have collar tentacles and blend ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature03382
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  • 9
    Electronic Resource
    Electronic Resource
    Axial patterning in cephalochordates and the evolution of the organizer (2007)
    [s.l.] : Nature Publishing Group
    Nature 445 (2007), S. 613-617 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The organizer of the vertebrate gastrula is an important signalling centre that induces and patterns dorsal axial structures. Although a topic of long-standing interest, the evolutionary origin of the organizer remains unclear. Here we show that the gastrula of the cephalochordate amphioxus ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature05472
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  • 10
    Electronic Resource
    Electronic Resource
    Differential gene expression and intracellular mRNA localization of amphioxus actin isoforms throughout development: Implications for conserved mechanisms of chordate development (1997)
    Springer
    Development genes and evolution 207 (1997), S. 203-215 
    Details
    ISSN: 1432-041X
    Keywords: Key words Amphioxus ; Actin ; Tissue-specific gene expression ; Chordate evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The cephalochordate amphioxus is thought to share a common ancestor with vertebrates. To investigate the evolution of developmental mechanisms in chordates, cDNA clones for two amphioxus actin genes, BfCA1 and BfMA1, were isolated. BfCA1 encodes a cytoplasmic actin and is expressed in a variety of tissues during embryogenesis, beginning in the dorsolateral mesendoderm of the mid-gastrula. At the open neural plate stage, BfCA1 transcripts accumulate at the bases of the neuroectodermal cells adjacent the presumptive notochord. The 3’ untranslated region of BfCA1 contains a sequence that is similar to the ”zipcode” sequence of chicken β-cytoplasmic actin gene, which is thought to direct intracellular mRNA localization. BfCA1 is also expressed in the notochord through the early larval stage, in the pharynx and in the somites at the onset of muscle-cell differentiation. BfMA1 is a vertebrate-type muscle actin gene, although the deduced amino acid sequence is fairly divergent. Transcripts first appear in the early neurula in the somites as they begin to differentiate into axial muscle cells and persist into the adult stage. In young adults, transcripts are localized in the Z-discs of the muscle cells. Smooth muscle cells around the gill slits and striated muscle cells in the pterygeal muscle also express BfMA1; however, there is never any detectable expression in the notochord, which is a modified striated muscle. Together with the alkali myosin light chain gene AmphiMLC-alk, the sequence and muscle-specific expression of BfMA1 implies a conserved mechanism of muscle cell differentiation between amphioxus and vertebrates. Evolution of the chordate actin gene family is discussed based on molecular phylogenetic analysis and expression patterns of amphioxus actin genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004270050109
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