MASTER THESIS Biomimetic potential of sponge ... - IAP/TU Wien

concentration there facilitates secondary bio-silification, i.e. to fuse spicules together in a
silica-based matrix (Wang et al., 2012c) (cf. Figure 5b).
Figure 5: Contrasting biosynthesis and morphology of demosponge- and hexactinellid-spicules ((Müller et al.,
2007a) (Wang et al., 2012b) (Wang et al., 2012c)) (a) Biosynthesis commences in specialized cells called
sclerocytes in both classes of siliceous sponges. After the initial longitudinal growth, immature spicules are
extruded to the extracellular space where appositional, and further longitudinal, growth take place. Thereafter,
all lamellae of each individual spicule are fused together (biosintering) in demosponges (c-f), while in many
hexactinellids a similar process cross-links adjacent spicules (b). Apart from the innermost region, the layers of
most hexactinellid spicules remain distinct. © by (Wang et al., 2012b)(a), (Wang et al., 2012c) (b, f) and (Müller
et al., 2007a) (c-e)
It is interesting to notice that individual spicules can largely vary in their dimension.
Though the terms microsclere and megasclere admittedly give a clear hint to size
differences, these terms come nowhere close to correspond to the differences that span six
orders of magnitude: The limit between micro-and megascleres is usually indicated to be in
the range of tens or hundreds of micrometers ( microscleres < 100 µm and megascleres >
300 µm (Wang et al., 2009), 20 µm (Wang et al., 2012c)). Therefore, the size of megascleres
extends over 4-5 orders of magnitude, while microscleres are much more uniform in size.
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