The Pink Magnet Slug

Zoologger has a feature on the Pink Magnet Slug. The nudibranch Rosy tritonia isn’t exactly cuddly-looking, nor is it brightly patterned like its recently discovered cousin, the Sea Pancake, but it has an enviable perk: its entire body is a compass.

The rosy tritonia is one of the growing list of animals that are known to sense Earth’s magnetic field to help them navigate. It was first seen doing so in 1987.
The discovery raised two questions: how does it do it, and why? A. O. Dennis Willows of the University of Washington in Friday Harbor has spent the past two decades trying to get answers.
Many animals use localized sensors to detect magnetic fields – some birds seem to use special chemicals in their eyes, for instance – but Willows says the rosy tritonia has sensors throughout its body.
Early experiments identified pairs of neurons in the rosy tritonia’s brain that fired more, or in some cases less, when the direction of the magnetic field was changed. But those neurons aren’t the sensors: cutting the nerves running into the brain stopped the neurons responding.
Willows and colleagues have now tried recording from peripheral nerves in animals that have had their brains removed. Nerves from all over the body responded when he rotated the magnetic field. The response was stronger on the right side: 43 axons responded on the right but only 25 on the left.
Because so many nerves responded, Willows thinks the rosy tritonia must have sensors distributed throughout its body. But he doesn’t know what sort of sensors: it might be a chemical like the one birds use, or small bits of magnetic metal embedded in cells.

Read more about the Pink Magnet Slug at New Scientist.