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Hawaiian Bobtail Squid Glows from Below

By Kate Ruder

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Oceans
Weird Science

The tiny Hawaiian bobtail squid Euprymna scolopes hunts for shrimp at night and buries itself in the sand during the day.
The Hawaiian bobtail squid beams light from its belly to camouflage its dark shadow from predatory fish on the sea floor, and now scientists know how.

The small squid is about two inches long and swims in shallow waters around Hawaii. It searches for and feeds on shrimp at night, when moonlight would cast the squid’s shadow on the sea floor below and alert fish that might eat the squid.

Researchers have discovered that the squid has developed specialized proteins in its belly that reflect light given off by luminescent bacteria that live on the squid. The reflected light camouflages the squid’s shadow, and the squid is effectively masked in its own moonlight glow.

The new proteins, which the researchers dubbed “reflectins,” are found in a special organ in the squid’s belly called the light organ reflector. In addition, similar proteins are found around the squid’s eyes and could help the squid see its food.

“The proteins are unlike anything that anyone has seen before in both their composition and behavior,” says Wendy J. Crookes of the University of Hawaii-Manoa in Honolulu, who was a member of the research team.

You or I probably could not see the squid’s beam of belly light with the naked eye. The researchers use specialized instruments in the lab to measure the squid’s glow.

The squid proteins might someday be used to manufacture nanomaterials for optics and human medicine, although even the researchers admit that this is speculative.

Crookes, W. J. et al. Reflectins: The Unusual Proteins of Squid Reflective Tissues. Science 303, 235-238 (January 9, 2004).

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