While diving in the Indo-Australian Ocean, a slender object with bandings on its back catches your eye. What could it be👀? You just met the Annulated Sea Snake Hydrophis cyanocinctus (Daudin, 1803) 🌊🐍 and after reading the following text, you might change your view on your encounter with this fascinating creature.
Sea snakes are generally misunderstood due to most people's fear of snakes. No worries though, sea snakes are often quite chill in the presence of humans😎. Although they are often highly venomous, they tend to reserve the venom for catching prey, and most snake bites are the last line of defensive behaviour . As hinted by its common name, the Annulated Sea Snake are olive or greyish yellow sea snakes encircled with bluish-black bands. They live in shallow and deep water of the coastal areas of Papua New Guinea, Indonesia, The Philippines, India, Southeast Asia and all the way to the Persian Gulf. Although reports of this species accidentally caught by prawn trawlers are rather common, natural encounters with divers are rare🧐.
Compared with marine mammals (e.g. dolphins and whales) that readapted to a marine lifestyle about 65 million years ago, the sea snakes are relatively new members to the aquatic community as they separated from their terrestrial snake ancestors approximately 16 million years ago😯. And just like marine mammals, they have evolved specialized features to support a full marine lifestyle. The annulated sea snake is viviparous, which means the mother will give birth to live young when the embryos are fully developed inside the mother’s body. However, some of its relatives in the Hydrophiinae are ovoviviparous where living young are born from eggs which are hatched within the body of the parent. 🥚Like most of the sea snakes, the Annulated Sea Snakes can absorb oxygen in water through their skin. This feature allows them to submerge under water for up to eight hours🤯. Their nostril openings are located on the upper side of the nose and can close up to keep water out when underwater. When they come up for air, the holes open up so they can breathe. This helps them to swim in areas with big waves without drowning.
If you look closer to the skull of some sea snakes in the 𝘏𝘺𝘥𝘳𝘰𝘱𝘩𝘪𝘴 group, some of them present a mysterious foramen (latin word for “hole”) on the top of their skull💀. The position of the skull foramen resembles those of several lizard species which contain a light-sensitive organ called the pineal eye. However, unlike those in lizards, there is no foramen on the sea snake’s skin (only in the skull) and it is believed that snakes have lost their pineal eyes 100 million years ago according to the fossil record🤔. Therefore, scientists decided to investigate other possible functions of the skull foramen🔍. Surprisingly, a 2019 study on the Annulated Sea Snake revealed that the structure is actually related to the species’ unique respiratory system, helping them in making a step forward to master breathing underwater. The image obtained through CT scanning of specimens revealed that there is a network of blood vessels surrounding the top of the snake’s skull, with a large blood vessel (or a pair) passing through the foramen, and connecting directly to the brain of the snake🧠. As mentioned above, sea snakes can breathe through their skin. Oxygen in seawater goes through their skin and into their blood vessels. The complex network of blood vessels on the skull of the Annulated Sea Snake could enhance uptake of oxygen directly to its brain😲. Now that scientists have unveiled the secrets behind the superpower of the Annulated Sea Snakes, it will not be surprising that a similar vessel network could be found in other species of sea snakes.
Can you think of another group of aquatic species that uses a similar breathing morphology? That’s right: fishes, with the presence of gills which also involve a complex network of blood vessels to enhance oxygen uptake🐟. It is remarkable to note how animals that live in water have developed similar features, even if they are not closely related and had independent evolution to adapt to the aquatic environment. Do come to the Biodiversity Museum and see these features yourself. You might even discover new things that scientists haven’t figured out yet!😶🌫️
Text: Bonnie
Comments