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  • 1990-1994  (2)
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  • 1
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The compass depressors are bands of soft tissue which connect the compass ossicles of the echinoid lantern to the inner edge of the test. They are essentially ligaments with on one side a thin layer of muscle cells. The ligamentous component consists mainly of a parallel array of collagen fibrils with interspersed 12 nm microfibrils. The most notable cellular constituents are granule-containing cell bodies and their processes which resemble the juxtaligamental cells that have been found in all echinoderm mutable collagenous tissues and which may control the tensility of these tissues. The muscle cells occupy about 8% of the total cross-sectional area of the compass depressor and are located in a richly innervated pseudostratified myoepithelium. When subjected to constant low loads in creep tests the compass depressor stretches to a fixed length beyond which there is no further extension. The length at this creep limit coincides with the maximum length to which the compass depressor is stretched by natural movements of the intact lantern. Stress-strain tests show that treatment with 1 mM acetylcholine or 100 mM K+ ions can increase reversibly the stiffness of the compass depressor to an extent that cannot be due to contraction of the myoepithelium, suggesting that the mechanical properties of the ligament are under physiological control. Tension-length data on the myoepithelium suggest that it generates a maximum active tension when the compass depressor is stretched to the creep limit. The implications of these results for the function of the compass depressors are discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The Aristotle's lantern, or masticatory apparatus, of regular sea-urchins is a complex musculo-skeletal system which is thought to have contributed significantly to the evolutionary success of these animals. This paper gives an account of the antomical relationships and functional morphology of both skeletal and soft tissue components in the lantern and related structures of the sea-urchin Stylocidaris affinis (Cidaridae), and compares these features with their equivalent in the previously described lantern of the sea-urchin Paracentrotus lividus (Echinidae, Camarodonta). There are major differences in the skeletons of these lanterns which involve mostly the arrangement and morphology of elements participating in movement, i.e. joints and articular surfaces, and which highlight the generally heavier and less mobile nature of the lantern in the Cidaridae. There are remarkably few differences, however, in the microstructure of the skeletal stereom. Significant dissimilarities were found in the anatomical arrangement of muscles and ligamentous structures and in their macro- and microstructure. The implications of these morphological features for the functioning of the lantern of the Cidaridae are discussed in the context of an integrated model of lantern biomechanics.
    Type of Medium: Electronic Resource
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