Click to view This gigantic sea sponge has an exoskeleton made of glass rods, and each rod can grow up to a meter in length. In the deep sea, these massive sponges contain a menagerie of other tiny lifeforms, all dependent on their sea sponge hosts for something in short supply far under the water. They need light - and some sponges have a evolved a way to provide it using fiber optics.Sea sponges are among the most primitive animals on Earth. They don't move and don't have differentiated body structures. They basically have organized groups of cells living in an exoskeletal framework. Glass sponges build their exoskeletons from silica and create elaborate shapes from glass-like rods called spicules, pictured below.
Some glass sponges get incredibly large, with spicules a meter long and surprisingly wide. No one was really sure why the sponges and their spicules sometimes grew so large. It turns out another mystery about sea sponges was the key to solving this one. The sponges often have millions of tiny organisms living inside them, like glass shrimp and algae. Those organisms need light to survive, and if you were writing a Lovecraftian horror story, there are worse analogies you could use than, "Dark as the inside of a sea sponge." Some curious German scientists stuck photosensitive paper inside glass sponges, then shined a light into their spicules. Sure enough, the paper showed light exposure patterns consistent with the spicule positions. Those glass-like tubes are more glass-like than we thought. The sponges use them to transmit light (a rare commodity deep beneath the ocean) down into their own bodies, where it shines (dimly) onto their wee symbiotes. The spicules act exactly like fiber optic cables, even bending the light around curves. They're still waiting for FiOS though. Images by: National Biological Information Infrastructure/Randolph Femmer ; Walla Walla University/Dave Cowles. Nature's 'fibre optics' experts. [BBC News]