Sea Snake Scales May Have Special Sensing Powers

Structures on individual scales may be capable of sensing vibrations in the water, helping the animals 'feel' objects up ahead.

Photo: An Olive sea snake (Aipysurus laevis) dives after taking a breath at the water's surface. Sea snakes are fully aquatic reptiles that live their whole lives at sea. Little is known about how they sense their underwater environment. Credit: Chris Malam After sea snakes left their land-bound cousins behind and took to water some 9 to 20 million years ago, they may have evolved a sense mechanism that lets them feel vibrations in the water and gather information about objects in the distance.

That was the suggestion behind a new study led by scientists at the University of Adelaide, who took a closer look at structures on the head of a snake called scale sensilla.

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Scale sensilla are raised structures on the heads of land snakes and some lizards. The creatures use them to sense objects in front of them directly, by touch (see photo below).

With the help of microscope imaging systems, the researchers studied 19 snake species – from land-based, to seafaring, to semi-aquatic – and gauged the number of scale sensilla present on individual scales in the creatures' heads as well as the shapes of the structures.

The researchers found that on sea snakes the scale sensilla tended to jut out more from the scales and were shaped differently – more like domes – than those of land snakes.

What's more, the scale sensilla covered larger areas of a sea snake's body.

Shown is the head of a Beaked sea snake (Hydrophis schistosus) and a close up of a single scale on head. Each scale has many 'scale sensilla' that protrude from it's surface. These small organs may allow aquatic snakes to 'feel' their environment. Credit: Jenna Crowe-Riddell

Those differences suggested to the researchers that in sea snakes the structures have the potential to function as sensory surfaces.

"We believe sea snakes use these organs to sense objects at a distance by 'feeling' movements in the water," said the lead author of the study, University of Adelaide PhD student Jenna Crowe-Riddell, in a statement. "This hydrodynamic sense is not an option for land animals. In water, a new way of sensing the environment becomes possible."

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Scientists know a lot about sea snakes, the curious creatures that look like they should be on land but spend most of their lives swimming, diving, coming topside to breathe the air, and tracking down fish to eat. Less well known, say the researchers, are their sensory capabilities while in the deep.

"What we now need to do is to investigate the physiology of these scale sensilla and demonstrate exactly what they can sense," said the lead scientist of the study, Kate Sanders.

"If they are hydrodynamic tactile sense organs, as we suspect," she said, "then by comparing them to the scale sensilla of closely related land snakes we can start to understand how evolution has changed these organs from direct-touch sensors to distance vibration sensors that work underwater."

Details of the study have been published in the Royal Society journal Open Biology.