Functional morphology of Tethya species (Porifera) 2. Three-dimensional morphometrics on spicules and skeleton superstructures of T-minuta

M. Nickel, Eric Bullinger, F. Beckmann

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

The biomechanics of body contraction in Porifera is almost unknown, although sponge contraction has been observed already in ancient times. Some members of the genus Tethya represent the most contractile poriferan species. All of them show a highly ordered skeleton layout. Based on three main spicule types, functional units are assembled, termed skeleton superstructures here. Using synchrotron radiation based x-ray microtomography and quantitative image analysis with specially developed particle and structure recognition algorithms allowed us to perform spatial allocation and 3D-morphometric characterizations of single spicules and skeleton superstructures in T. minuta. We found and analyzed three skeleton superstructures in the investigated specimen: (1) 85 megasclere bundles, (2) a megaster sphere, composed by 16,646 oxyasters
and (3) a pinacoderm–tylaster layer composed by micrasters. All three skeleton superstructures represent composite materials of siliceous spicules and extracellular matrix. From structure recognition we developed an abstracted mathematical model of the bundles and the sphere. In addition, we analyzed the megaster network interrelation topology and found a baso-apical linear symmetry axis for the megaster density inside the sphere. Based on our results, we propose a hypothetical biomechanical contraction model for T. minuta
and T. wilhelma, in which the skeleton superstructures restrain physical stress generated by contraction in the tissue. While skeletal structures within the genus
Tethya have been explained using R. Buckminster Fullers principle of tensegrity by other authors, we prefer material science based biomechanical approaches, to
understand skeletal superstructures by referring to their composite material properties.
Original languageEnglish
Pages (from-to)225-239
Number of pages15
JournalZoomorphology
Volume125
Issue number4
DOIs
Publication statusPublished - 2006

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Keywords

  • porifera
  • microtomography
  • tethya
  • biomechanics
  • skeleton superstructure
  • tensegrity
  • composite materials
  • synchrotron radiation

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