|A BALANCING ACT: Ctenophore statocysts (1), consist of a statolith composed of lithocyte cells and four compound cilia called balancers that serve as the statolith’s legs. As the animal tilts in the water, the statolith falls to the side, bending the balancers and triggering a mechanical signal to adjust the frequency of ciliary beating along the ctenophore’s eight comb plates. Other invertebrates have a more complex statocyst, in which a sphere of sensory hair cells detects the movement of a statolith floating within it (2). When the statolith falls against a hair cell, it triggers an electrical impulse that sends the information to the animal’s central nervous system.|
|HAIRLINE: Modified epithelial cells called hair cells—similar to those in the mammalian inner ear—are the work horses of the lateral line in fishes. Hair cells connect to afferent neurons and are grouped together into structures called neuromasts whose hairs are covered by a jelly-like secretion called the cupula. When moving water or vibrations trigger neuromasts, which sit inside pores on the head, body, and tail of the fish, hair cells stimulate neurons to relay information about velocity or acceleration to sensory ganglia distributed through the fish’s body.|
MAGNETO #1: There are two prominent ideas for how some animals are able to detect the Earth’s magnetic fields. Diverse species have magnetite-containing cells, which are thought to be innervated and contain surface ion channels that are physically pulled open as magnetic fields tug on magnetite tethered to the cell membrane or the channel itself.
MAGNETO #2: Birds and possibly other animals also appear to “see” magnetic fields through the visual system. Proteins called cryptochromes that reside in the eye’s cones can form a pair of radicals (unpaired electrons), whose spin is affected by magnetic fields and may affect the animal’s sensitivity to light.
HEAT SENSE: Pit organs consist of a large, hollow, air-filled outer chamber and a smaller inner chamber separated by a membrane embedded with heat-sensitive receptors. The receptors are innervated by the trigeminal ganglia (TG), which transmit the infrared signals to the brain.
|ELECTRIC SLIDE: Sharks and other cartilaginous fish have highly specialized electroreceptive organs called the ampullae of Lorenzini. These bundles of sensory cells, situated at the end of jelly-filled pores in the skin, detect electric fields in the water surrounding the fish and send signals to the brain.|
ILLUSTRATIONS BY LAURIE O'KEEFE
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