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

shape of spicules, for most spicule-morphologies observed in the fossil record can still be
found in living organisms today, i.e. they occur in extant species (Hinde, 1887-1893)
(Wiedenmayer, 1994). This clearly demonstrates that this architecture is favourable under a
variety of conditions, for sponges have survived long geological times and concomitantly
changing environments (Uriz, 2006) This striking adaptability makes them very competitive
in regions with strong anthropogenic influences. In the western central pacific, e.g.,
encrusting demosponges of the genus Terpios have been found to overgrow (and thereby
kill) coral reefs in pollution-stressed zones off the coasts of Guam, Micronesia (Bryan, 1973),
and Japan (Rützler & Muzik, 1993).
Spicules are, however, not always just “needles” scattered throughout the body of
sponges. On a larger scale, individual spicules can be fused together to form massive
endoskeletons (cf. Figure 6h) in some hexactinellid sponges, but more frequently they occur
unattached throughout the body of sponges, interlocked (Figure 7c) or joined by the protein
spongin (Butler, 1961) (Uriz, 2006). Especially in sponges with rigid skeletons like Venus’
Flower Basket (Euplectella aspergillum) individual spicules may be barely discernible (cf.
Figure 6d,h, Figure 7d). In contrast loosely attached or unattached spicules of other sponges
readily scatter around the site upon death and disintegration of the sponge (Butler, 1961).
The morphology of spicules has been widely used for identification of genera and species
(Butler, 1961) (Dohrmann et al., 2011) (Li, 1987). However this is far from trivial, since one
individual sponge usually contains spicules with differences regarding number of symmetry
axes, surface, size, ornaments and extremities while similar spicules are shared among
various genera. The most basic distinction has been to distinguish larger spicules
(megascleres) from smaller microscleres (Lévi, 1973). Although the concept has been shown
to be flawed, since calcareous spicules do not represent this dichotomy and in siliceous
sponges microscleres exceeding the size of megascleres have been found (Uriz, 2006), it is
still widely used (Wiens et al., 2011) (Valisano et al., 2012) (Voznesenskiy et al., 2011).
The main purpose of this classification is nowadays a functional one. Megascleres are
essential for the architecture of the spongial skeleton, while the lack of microscleres, which
are considered accessory skeletal elements, does not seem to involve any conceivable
disadvantage for a sponge (Uriz et al., 2003). Another basic distinction regards the number
of axes of symmetry (cf. Figure 4). While megascleres of demosponges either are monaxons
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