Fig. 8
Microstructures of the Sabellaria alveolata bioconstruction in plane-polarized light photos (a, c, e) and between crossed-polarized photos (b, d, f). The internal part of the worm tubes (in white) has been redrawn. (a, b) Two tubes with different diameters. Note the increase of the grain size outside the tube; (c, d) Sets of small-scale worm tubes. Tube grains are very fine-grained; (e, f) Cross-section of a tube in a plane parallel to its vertical development. Note the perfect alignment of elongated grains along the tube wall