Sea snakes’ sixth sense

By Georgie Meredith 14 June 2016
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Sea snakes have evolved an extra sense to feel movement underwater, according to new research.

SENSORY SCALES ON sea snakes are far more developed than previously thought, allowing them to sense vibrations underwater, a new study has found.

Researchers at the University of Adelaide in South Australia looked at 19 species of snakes, including fully-aquatic, semi-aquatic and land species, and measured the coverage of tiny and poorly understood structures on their heads known as scale sensilla.

“Land snakes and many lizards have small raised structures on the scales on their heads, called scale sensilla, that they use to sense objects by direct touch,” explained Jenna Crowe-Riddell, University of Adelaide PhD student and lead author of the study.

Sea snake sensilla

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 its surface, these small organs may allow aquatic snakes to ‘feel’ their environment. Scale bar, 3 mm. (Photo credit: Jenna Crowe-Riddell)

“We found that the scale sensilla of sea snakes were much more dome-shaped than the sensilla of land snakes, with the organs protruding further from the animals’ scales, potentially making them more likely to be able to sense vibrations from all directions.”

Sea snakes evolved from land-living snakes, taking to life in the sea between 9 and 20 million years ago.

Until now, little has been known about the underwater sensory perception of the snakes. 

“Every movement of a fin or flipper generates vibrations underwater, like when you drop a stone into a pond and the surrounding ripples spread to every corner of the pond,” said Jenna.

Sea snake sensilla

Lead author Jenna Crowe-Riddell observes a juvenile stokes sea snake (Hydrophis stokesii) (Photo credit: Ruchira Somaweera)

Future experiments could provide important information on the evolution of both touch and hydrodynamic receptors, commented Shaun Collin, Deputy Director of University of Western Australia’s Ocean Institute.

“The need to detect small hydrodynamic disturbances will be important for avoiding predation and detecting potential food objects, especially under conditions when some of the other sensory modalities may not be as useful,” said Shaun, who wasn’t involved with this study.

“It will be interesting to explore the physiological function of these raised sensillae,” he said.

Potential impact

The study, published in the Royal Society journal Open Biology, highlights the potential impacts on sea snake populations from man-derived disturbances such as motor boats and seismic surveys.

According to the researchers, the next step is to investigate the physiology of these scale sensilla and demonstrate exactly what they can sense.

“If they are hydrodynamic tactile sense organs, as we suspect, 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,” said Dr Kate Sanders, another co-author of the study.