Heart cockles are multi-colored and host photosynthetic algae in their shells
Dakota McCoy
A heart-shaped mollusk has developed tiny windows that work like fiber optic cables, the first known example in nature.
Heart cockles (Corculum cardissa) are bivalve molluscs, a bit like clams, that have a symbiotic relationship with the photosynthetic algae that live inside them. Algae have a safe home, they get light for photosynthesis and provide nutrients to their hosts.
Unlike other bivalves, heart cockles do not spread their shells open, but they somehow direct light to the interior even when closed.
now, Dakota McCoy At the University of Chicago and his colleagues, they discovered that the shells of heart cockles contain transparent calcium carbonate crystal structures that act like bundles of optical fibers, allowing light inside to bathe the algae. “If you don’t have to open it and just have a clear window, that’s a very safe way to irradiate your algae,” says McCoy.
The researchers looked at parts of different cockle shells and the transparent structures inside them, as well as the intensity and color of the light passing through them. They found that the windows were made of long, thin fibers of a mineral called aragonite, through a layer of calcium carbonate, which lets in twice as much photosynthetically useful light as it filters harmful ultraviolet light. “We put on sunblock because UV causes mutations and cancer. Cockroaches in the heart are using these windows as sunblock,” says McCoy.
Heart cockle shells illuminated from within to reveal transparent windows in their shells, which can be small triangles (left) or stripes (right).
Dakota McCoy
Although aragonite strands are similar to manufactured optical fiber, they lack an insulating and protective sheath called a cladding, but they transmit light just as efficiently. This could serve as inspiration for uncoated fiber optic cables, which would be cheaper to manufacture.
The shells’ natural UV-blocking properties could also be used to help protect corals, which harbor photosynthetic algae like cockles inside them but are exposed to environmental stresses like light and heat, McCoy says.
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