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  • 1
    Digitale Medien
    Digitale Medien
    Size-related aspects of arm damage, tissue mechanics, and autotomy in the starfish Asterias rubens (2000)
    Springer
    Marine biology 137 (2000), S. 59-70 
    Details
    ISSN: 1432-1793
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  Arm damage is a widely reported but superficially investigated aspect of the biology of the starfish Asterias rubens L. In the present study, the incidence of arm damage was surveyed in populations of A.  rubens at two sites in the Firth of Clyde, Scotland, and three sites in Gullmarsfjorden, Sweden. The mean (±SD) incidence across all sites of individuals with basal arm damage (resulting from detachment at the basal autotomy plane) was 19.69 ± 8.86%, the incidence of those with distal arm damage (resulting from amputation at more distal levels) was 7.74 ± 10.01%. The mean incidence of arms with basal damage was 5.28 ± 4.12%, of those with distal damage 1.83 ± 2.45%. There was a significant negative correlation between size and the incidence of basal damage at all but one site, but no significant correlation between size and distal damage at any site. Mechanical tests on specimens of the aboral body wall from the basal region of the arm (which included the autotomy plane) and from a more distal region revealed that with increasing body size there was a significant increase in yield stress, ultimate stress and Young's modulus (stiffness) but no significant change in yield strain and ultimate strain. There was no significant difference between the relationships for basal and distal specimens. It is hypothesised that in larger individuals increased mechanical toughness replaces autotomy as an effective antipredator strategy. Using two methods to induce autotomy, a significant positive correlation between size and the delay between the onset of stimulation and arm detachment was found; this may represent a size-related decline in the efficiency of the autotomy mechanism through the relaxation of selection pressure. Since size is an unreliable indicator of age in A.  rubens, the trends identified herein can be interpreted only tentatively as age-associated phenomena.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002270000299
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  • 2
    Digitale Medien
    Digitale Medien
    Functional morphology of the autotomy plane of the brittlestarOphiocomina nigra (abildgaard) (ophiuroidea, echinodermata) (1978)
    Springer
    Zoomorphology 91 (1978), S. 289-305 
    Details
    ISSN: 1432-234X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Despite the evident efficiency with which ophiuroids discard their arms, there has been no attempt to understand how the arm is equipped anatomically to achieve and recover from autotomy. A light microscope study of the breakage plane ofOphiocomina nigra revealed a series of features which can be interpreted as adaptations for the process of autotomy. The epidermis splits at a constriction which acts as a pre-determined line of least resistance and which serves to leave lateral flaps for the protection of the retained wound surface. The radial nerve breaks at a level where its cross-sectional area is least and which avoids the ectoneural ganglion; at this point the nerve is attached to the floor of the epineural canal by a collagenous structure which may facilitate its rupture. The lateral compression of the radial haemal canal at the breakage plane is believed to assist its closure after autotomy. The sphincters of the radial water vascular canal are described and it is suggested that since they occur just proximal to the breakage plane, one of their functions may be to seal off the canal after autotomy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00999817
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  • 3
    Digitale Medien
    Digitale Medien
    Morphological and mechanical aspects of fission in Ophiocomella ophiactoides (Echinodermata, Ophiuroida) (1984)
    Springer
    Zoomorphology 104 (1984), S. 310-322 
    Details
    ISSN: 1432-234X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary During fission the ophiuroid Ophiocomella ophiactoides splits across the disc into two halves each of which regenerates to form a complete individual. This paper describes the gross anatomy of the fission plane and the histology, ultrastructure, and mechanical properties of key structures transected during fission. Rupture of the disc integrument appears not to be facilitated by a pre-determined plane of weakness. Comparison of naturally split and artificially split animals showed that at fission a mechanism operates which restricts breakage to the interradial plane of two jaws. The interradial plane is subtended mainly by collagenous ligaments and by muscles linked to the skeletal components by basal lamina-like tendinous fibres. No fission-related adaptations could be identified in the oesophagus, circumoral nerve ring, or circumoral water vascular canal. On the basis of creep tests on isolated preparations of the disc integrument and jaw-frame and the responses of these preparations to ionic manipulation, it is suggested that their behaviour is dominated by collagenous elements that can undergo actively controlled changes in their mechanical properties. A hypothesis is presented which proposes a role for such a mechanism in the initiation and facilitation of fission.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00312013
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  • 4
    Digitale Medien
    Digitale Medien
    A spicule-reinforced contractile mesentery: organisation and mechanical behaviour of the exterior coelomic septum of Stylocidaris affinis (Echinodermata, Echinoida) (2000)
    Springer
    Zoomorphology 120 (2000), S. 119-133 
    Details
    ISSN: 1432-234X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  The exterior coelomic septum (ECS) is a mesentery-like structure that encloses the lantern of regular sea-urchins and connects it to the inner surface of the test. This paper describes the ultrastructure and microarchitecture of the ECS in Stylocidaris affinis (Cidaridae, Echinoida) and provides information on its contractile and passive mechanical properties. The ECS forms five interambulacral pouches each of which has adthecal (test-facing) and adambulacral (ambulacrum-facing) walls. The ECS wall comprises two coelothelia separated by a layer of connective tissue. The outer coelothelium is a single layer of monociliated cuboidal peritoneocytes and basally located axon-like processes. The inner coelothelium is a single layer of squamous peritoneocytes overlying axon-like processes and, in the adthecal regions only, parallel arrays of elongated myocytes orientated obliquely or horizontally. The intraseptal connective tissue consists mainly of collagen fibrils with sparsely distributed spherule cells and cells containing heterogeneous vesicles. In the adambulacral regions of the ECS hollow beaded microfibrils 20–23 nm in diameter form fibre-like aggregations. This layer also contains calcite spicules of variable size, shape, abundance and orientation. Isolated preparations of the ECS show concentration-dependent contractile responses to K+ ions and acetylcholine. The magnitude of the contractile force varies with the vertical position of the lantern (which determines the starting length of the ECS) in an unusual pattern. Cyclical loading-unloading tests indicate that, as the lantern is raised, the ECS shows low stiffness until the lantern reaches its normal resting position. It is concluded that the adthecal regions of the ECS help to set a limit to lantern retraction and that their contractility assists the protractor muscles in exerting a downward pull on the lantern.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004350000029
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  • 5
    Digitale Medien
    Digitale Medien
    The compass depressors ofParacentrotus lividus (Echinodermata, Echinoida): ultrastructural and mechanical aspects of their variable tensility and contractility (1992)
    Springer
    Zoomorphology 112 (1992), S. 143-153 
    Details
    ISSN: 1432-234X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01633105
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  • 6
    Digitale Medien
    Digitale Medien
    The tendons of Ophiocomina nigra and their role in autotomy (Echinodermata, Ophiuroida) (1987)
    Springer
    Zoomorphology 107 (1987), S. 33-44 
    Details
    ISSN: 1432-234X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary In the arm of the ophiuroid Ophiocomina nigra the intervertebral muscles are linked to the vertebral ossicles by tendinous connective tissue fibres. When an arm autotomizes, rupture of the tendons at one end (the autotomy insertion) permits each muscle in the autotomizing segment to separate cleanly from an ossicle while its other attachment (the non-autotomy insertion) remains intact. The anatomical relations, composition and function of the tendons were investigated by histochemical, electron microscopical and experimental methods. The tendons consist of a carbohydrate-rich secreted collagen derived from the basal lamina of the muscles. At autotomy their rupture is preceded and facilitated by an increase in extensibility, which represents the first evidence for variable tensility in an echinoderm connective tissue not composed of interstitial collagen. Granule-containing juxtaligamental cell processes are associated with the tendons of the autotomy insertions but are absent from the non-autotomy insertions. There appears to be widespread release of granules from these processes at autotomy. The results of a simple experiment implicate the juxtaligamental cells in the control of tendon extensibility and a possible mechanism for this control is presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00312127
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  • 7
    Digitale Medien
    Digitale Medien
    Organization and mechanical behaviour of myocyte–ligament composites in a sea-urchin lantern: the compass depressors of Stylocidaris affinis (Echinodermata, Echinoida) (1998)
    Springer
    Zoomorphology 118 (1998), S. 87-101 
    Details
    ISSN: 1432-234X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  Certain components of the jaw apparatus, or lantern, of regular sea-urchins form a ’compass system’ the function of which has still to be established. This system includes ten compass depressors (CDs) which connect the compass ossicles to the inner edge of the test. Previous studies focused on the CDs of euechinoid sea-urchins. This paper provides the first detailed account of the organization and mechanical behaviour of the CDs of a cidaroid sea-urchin, Stylocidaris affinis. The outermost layer of its CDs is a coelothelium comprising apical peritoneocytes, sparse subapical myocytes and two types of granule-containing cells. The central core of the CD is dominated by longitudinally orientated collagen fibrils arranged in bundles surrounded by networks of beaded microfibrils. Myocytes are scattered throughout the core and are always surrounded by a basal lamina which usually encloses the same two types of granule-containing cells observed in the coelothelium. Each CD is attached to the outer coelomic septum by a mesentery, both the connective tissue and coelothelia of which lack myocytes and granule-containing cells. From data on the relationship between the vertical position of the lantern and the passive and active forces developed by intact CD sets, it appears that the CDs resist elevation of the lantern above its ’resting position’ and that they develop a maximal contractile force when their length corresponds to that at the resting position. The connective tissue of the CDs has the capacity to undergo nervously mediated changes in stretch resistance, although this is expressed more weakly than in the euechinoid CDs. These results are related to current views on the physiological role of the compass system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004350050060
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  • 8
    Digitale Medien
    Digitale Medien
    The Aristotle's lantern of the sea-urchin Stylocidaris affinis (Echinoida, Cidaridae): functional morphology of the musculo-skeletal system (1993)
    Springer
    Zoomorphology 113 (1993), S. 173-189 
    Details
    ISSN: 1432-234X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00394858
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  • 9
    Digitale Medien
    Digitale Medien
    Mechanical properties of sea-urchin lantern muscles: a comparative investigation of intact muscle groups in Paracentrotus lividus (Lam.) and Stylocidaris affinis (Phil.) (Echinodermata, Echinoidea) (1998)
    Springer
    Journal of comparative physiology 168 (1998), S. 204-212 
    Details
    ISSN: 1432-136X
    Schlagwort(e): Key words Echinodermata ; Echinoidea ; Lantern of Aristotle ; Muscle mechanics ; Force-length relations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The jaw apparatus, or lantern, of sea-urchins contains five pairs of retractor and protractor muscles which are responsible for lantern displacement. Using intact retractor or protractor groups, the force-length relations of these muscles were compared in two taxonomically distant species, Paracentrotus lividus and Stylocidaris affinis. The total contractile forces generated by the muscles can be resolved into vertical and horizontal components. It was found that the vertical component of the retractors is maximal at a lantern position which is significantly lower (i.e. more protruded) in Paracentrotus than in Stylocidaris. Total forces generated by the retractors were in both species maximal at or above the lantern `resting positions'. In Paracentrotus alone, the total force-displacement curves tended to be bimodal. It is hypothesized that the retractors of Paracentrotus contain two populations of muscle fibres, one adapted for jaw opening and one for lantern retraction. No significant differences in the properties of the protractors of the two species could be identified. The lantern of Paracentrotus is more mobile than that of Stylocidaris and is able to exploit a wider range of food sources. This investigation has shown that the force-length relations of the lantern muscles match their differing working conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003600050138
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  • 10
    Digitale Medien
    Digitale Medien
    The juxtaligamental cells of Ophiocomina nigra (Abildgaard) (Echinodermata: Ophiuroidea) and their possible role in mechano-effector function of collagenous tissue (1979)
    Springer
    Cell & tissue research 197 (1979), S. 515-530 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Echinodermata ; juxtaligamental cells ; Collagenous tissue ; Ophiocomina nigra ; Neurosecretory cells
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary The intervertebral ligament of the brittlestar Ophiocomina nigra contains numerous cellular processes which belong to perikarya located on the outer surfaces of the ligament. These are described as the juxtaligamental cells and have been studied by light and electron microscopy. The cells are mainly concentrated in four pairs of ganglion-like nodes associated with the intervertebral ligament and in similar nodes adjacent to every other major connective tissue component of the arm. Although their histochemistry and ultrastructure indicate a neurosecretory function, they are anomalous in containing unusually large electron-dense granules probably associated with calcium. The ganglion-like nodes are innervated by hyponeural nerves, though synaptic contacts with the juxtaligamental cells have yet to be demonstrated. The function of the cells is discussed and it is suggested that they may be involved in the rapid loss of tensile strength which the intervertebral ligament sustains during arm autotomy. They may achieve this by controlling the availability of Ca2+ ions to the extracellular compartment of the ligament. A version of this paper was read at the U.K.-Eire Echinoderms Colloquium, Bedford College, London, in July 1978
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00233574
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