This glass sponge, a cousin of the barrel sponge, produced dense reefs in ancient seas that were shallow and warm. In modern times, the delicate animals were thought to exist only as fossils until explorers in the 1990s discovered large reefs of living relics.
from wikipedia “One ability [Hexactinellid sponges] do possess is a unique system for rapidly conducting electrical impulses across their bodies, making it possible for them to respond quickly to external stimuli . . . They work as optical fibres that are surprisingly similar to those used in modern telecommunication networks and could even be more handy than the artificial versions. The biological fibres of the sponge conduct light beautifully when they are illuminated, and use the same optical principles that modern engineers use to design industrial fibre optics.
Despite not having the ultra-high transparency needed for telecommunication networks, they do have other advantages; unlike commercial fibre, it is possible to tie them in tight knots without them cracking or breaking. Another advantage is the fact that these biological fibres are produced by chemical deposition at the temperature of seawater. For the moment, human fibre optics can only be produced with a high-temperature furnace and expensive equipment.”