Heart-shaped mollusks with window-like structures that function as optical fibers

Heart-shaped mollusks have evolved tiny windows that function like fiber optic cables, the first known examples in nature.

Heart monkey (Corculum Cardissa) are bivalves that look a bit like shellfish and have a symbiotic relationship with the photosynthetic algae that live inside them. Algae have a safe home, receive light, perform photosynthesis, and provide nutrients to their hosts.

Unlike other bivalves, cockles do not open their shells wide, but they somehow concentrate light inside even though they remain closed.

now, dakota mccoy Researchers at the University of Chicago discovered that cockles have transparent calcium carbonate crystal structures inside their shells that act like bundles of optical fibers, trapping light inside and showering it on the algae. “If you don't have to open it and you have a clear window, it's a very safe way to irradiate algae,” McCoy said.

The researchers examined shell fragments of various heart monkeys and the transparent structures within them, as well as the intensity and color of the light that passes through them. The researchers discovered that the windows are made of long, thin fibers of a mineral called aragonite, a type of calcium carbonate, which allows twice as much light, useful for photosynthesis, to pass through as it does harmful ultraviolet light. “We wear sunscreen because ultraviolet light can cause mutations and cancer, and the cockles use this window as a sunscreen,” McCoy said.

Aragonite threads are similar to manufactured optical fibers, but they transmit light just as effectively, although they lack a protective insulating sheath called a cladding. This could be an inspiration for cladding-free fiber optic cables that are cheaper to produce.

Shells' natural UV-blocking properties could also be used to protect corals. Like cockles, corals harbor photosynthetic algae inside, but McCoy said they are susceptible to environmental stresses such as light and heat.