The blue-banded sea snake (Hydrophis cyanocinctus) uses a complex system of large blood vessels in its head to draw in extra oxygen when it dives and swims underwater, according to new research.

Sea snakes must surface regularly to breathe but are among the most completely aquatic of all air-breathing vertebrates.

The highly venomous blue-banded sea snake, which lives in tropical waters of Southeast Asia, is found on coral reefs and warm coastal waters.

“For the first time, we describe this modified cephalic vascular network (MCVN) that provides this sea snake with a complementary supply of oxygen to the brain during submersion,” said Dr. Alessandro Palci, a researcher at Flinders University and the University of Alberta.

“Basically we found that this sea snake uses the top of its head as a gill to breathe underwater.”

The MCVN underlies a broad area of skin between the snout and the roof of the snake’s head.

“While the MCVN is structurally very different from the gills of fish and amphibians, its function is nonetheless quite similar, in that it provides a large surface area packed with oxygen-depleted blood vessels that can efficiently take in oxygen from the surrounding water,” Dr. Palci said.

“Our study expands understanding of the unusual cutaneous respiratory anatomy of sea snakes,” said Dr. Kate Sanders, from the University of Adelaide.

“Sea snakes have been extremely successful at adapting to a fully marine lifestyle, including the ability to absorb oxygen through their skin.”

“Now we have discovered this interesting feature in Hydrophis cyanocinctus by using microCT scans and computer modeling.”

“This feature probably allows these sea snakes to stay submerged for longer periods of time, which further research can test.”

The study is published in the journal Royal Society Open Science.

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Alessandro Palci et al. 2019. Novel vascular plexus in the head of a sea snake (Elapidae, Hydrophiinae) revealed by high-resolution computed tomography and histology. R. Soc. open sci 6 (9); doi: 10.1098/rsos.191099