Eyes Perceive Polarized Light

a brown horseshoe crab in shallow water with sand on top of their shell, one large compound eye see on the left

Biological Strategy

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Sense Light (Non-visible Spectrum) From the Environment

Living systems interact with each other and with their environments to gain information. Sometimes that information is in the electromagnetic spectrum. Wavelengths in the electromagnetic spectrum are also called the non-visible spectrum, because humans can’t detect them with the naked eye. These include ultraviolet (UV) light, infrared (IR) light, radio waves, and other wavelengths. Detecting within these spectra requires strategies beyond those used for visible light, so many living systems that depend on these signals have specialized organs to do so. For example, beetles that feed on burned trees have sensory organs that detect infrared radiation emitted by fires, enabling them to quickly locate a burned area.

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Crustaceans

Subphylum Crustacea (“crust”): Crabs, barnacles, shrimp, pillbugs

Some crustaceans, like pillpugs and woodlice, live on land, but most are found in the ocean. Their heads are distinctive among the arthropods: they have two pairs of antennae and three pairs of feeding appendages that help them hold and crunch food. Crustaceans also have a unique larval stage called the nauplius (named after the son of Poseidon) which has three pairs of legs and one eye. Most crustaceans are in class Malacostraca, which contains a wide range of species that live in mostly marine environments, like krill, lobster, and mantis shrimp.

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The eyes of horseshoe crabs reduce glare from sunlight because they contain an area that can perceive polarized light.

Image: Hayden / wikimedia commons /

Horseshoe Crabs mating

Image: Didier Descouens / Wikimedia commons /

Horseshoe crab - Limulus polyphemus - Limulidae - 55 cm (Dorsal view)

“The first aquatic species shown to be able to perceive polarized light was the horseshoe crab (Limulus polyphemus), a sea-dwelling chelicerate arthropod whose compound eyes were found by Dr T. H. Waterman in 1950 to contain an area that could analyze light polarization. Since then, Waterman’s continuing studies have revealed that many aquatic insects, crustaceans, fishes, and even mollusks such as squid and octopuses exhibit similar abilities that allow them to reduce glare or dazzling reflections caused by bright sunlight, just as we do by wearing polarized sunglasses.” (Shuker 2001:49)

Last Updated August 18, 2016

References

Book

The Hidden Powers of Animals: Uncovering the Secrets of Nature

Marshall Editions Ltd. | 26/02/2021 | Dr. Karl P. N. Shuker

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