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

That leaves us to talk of “siliceous sponges”, a subgroup of sponges that shares the
common, derived trait (synapomorphy) of a skeleton containing glass-spicules, among other
features. For readability, we will nonetheless continue to use the term “sponge”, specifying
the taxon when it is relevant. Commonly, researchers divide this group in Hexactinellids
(Glass sponges) and Demosponges (Borchiellini et al., 2001). While none of these
classifications is unchallenged, we will focus on the characteristics of sponges currently
described as the classes Demospongiae (Sollas, 1885) and Hexactinellida (Schmidt, 1870)
(Brien et al., 1973) (Tabachnick & Reiswig, 2002).
Demosponges include the vast majority of the 5,000-10,000 known extant sponges,
among them various species known as “common bath sponges” (e.g. Spongia officinalis var.,
Hippospongia equina). Not so common are glass sponges, with a mere 500 described species
(Tabachnick & Reiswig, 2002). Since, however, we know more about the dark side of the
moon than about their preferred habitat - the deep sea - these figures might change
drastically.
For (evolutionary) biologists, sponges are fascinating organisms, since they are believed
to bear resemblance with the Urmetazoa, the precursor of all animals. Intriguingly, sponges
have survived several evolutionary bottlenecks and changes in their environment over the
course of more than 540 million years - earning them sobriquets like “living dinosaurs” and
“living fossils” (Krautter et al., 2001) (Müller, 1998) (Steiner et al., 1993) (Steiner, 1994).
When siliceous sponges first emerged, oceans were richer in silica than today and hence
suggested Silicium to be included in the first skeletons. In fact silicatein, the enzyme driving
the formation of glassy sponge spicules, has likely heralded the era of biogenic mineral
deposition/ biomineralization (Li et al., 1998) (Müller et al., 2007a), a process that is
essential for the formation of all hard skeletons. This view has been challenged by the
discovery of fossils from Namibia representing 750 million year old, possibly calcareous
sponges (with Ca-based skeletons) that were reported in July 2012 (Brain et al., 2012).
Molecular data, however, still suggests that Hexactinellida are the phylogenetically oldest
extant animals (Müller, 1998) (Müller et al., 1995) (Kruse et al., 1997).
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