Glass sponge
The glass sponge builds its skeleton from tiny needles of glass and looks like a delicate, see-through little basket. It lives very deep and can grow extremely old, some more than a thousand years. Inside it a pair of small shrimp often lives, slipping in as youngsters and then never coming out again.
For scientists
Glass sponges (Hexactinellida) such as the Venus flower basket (Euplectella) build a skeleton of silica needles (spicules) fused into a stable lattice; its glass fibers guide light about as well as engineered optical fibers. They filter the finest particles in the cold deep sea and are among the longest-lived animals of all. A pair of cleaner shrimp often lives trapped inside for life, which in Japan is seen as a symbol of fidelity.
Source: Wikipedia
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