An unsuspecting mollusk with an adorable-looking shell may be hiding the secret to fast internet speeds.

Hearts (Corculum cardissa) have special windows in their shells that let light in through fiber-optic crystal structures, according to a new paper in the journal The nature of communication.

This evolutionary quirk is the first time fiber-optic cable bundles have been seen in a living organism, and it could inspire cheaper methods of making Internet fiber-optic cables.

“Optical cables and microlenses of the heart of a cockroach can inspire optical technologies,” the researchers wrote in the paper.

Like many molluscs, these cockles – which resemble clams – have a symbiotic relationship with the algae that live inside their shells. In these relationships, the algae gain access to light and food while living in the animal’s shell. In return, the mollusk eats the algae.

Other mollusk species that have this type of symbiotic relationship open their shells to let light in and allow the algae to photosynthesize. However, the ventricles remain closed. That’s because their shells are made of aragonite—a crystalline form of calcium carbonate—and they have special tiny windows in those shells that transmit light along optical fibers made of the mineral. This allows light to penetrate the shell without having to open it.

Fiber optic windows let in twice as much light as if they were holes. These windows also filter out ultraviolet wavelengths from light entering the shell that would kill the algae inside.

“Heart cockles transmit 11-62 percent of photosynthetically active radiation to their symbionts, but only 5-28 percent of potentially harmful UV radiation. Under each window, microlenses condense light to penetrate deeper into symbiont-rich tissue,” the researchers wrote.

The fiber optic cables we use for the Internet are made of thin strands of glass or plastic, each about the diameter of a human hair, that are bundled together in cables. Each strand of fiber has a core (where light travels) surrounded by a cladding that reflects light back into the core and prevents signal loss.

Aragonite in the shells forms a window thanks to the organic matrix that controls the growth of the shell and forms the mineral into long, fibrous crystals. In the window, these crystals are tied into a section of optical cables that focus the light, while in the rest of the shell, the aragonite is cross-linked and opaque.

“Inside each window, aragonite forms narrow fibrous prisms perpendicular to the surface. These bundled ‘fiber optic cables’ project images through the shell,” the researchers wrote. “Heartworms have developed transparent windows in their shells with what is, to our knowledge, the first example of bundled optic cables in a living creature.”

The researchers reported that the aragonite filaments strongly resembled human fiber optic cables, except without the sheath. This suggests that these natural fibers could inspire cheaper and more efficient ways to make optical cables for human use.

This is not the first time humans have stolen technology from the natural world.

The researchers wrote: “Previously, the glass tips of sponges inspired lightweight mechanical architectures, while the microlenses in spiders inspired anti-reflective polymer microchips.”

Reference

McCoy, DE, Burns, DH, Klopfer, E., Herndon, LK, Ogunlade, B., Dionne, JA, & Johnsen, S. (2024). Cordyceps transmit sunlight to photosymbiotic algae using bundled optical cables and condenser lenses. The nature of communication15(1).