Annulated Sea Snake

Head moderate. Diameter of eye less than its distance from the mouth in the adult. Rostral slightly more broad than deep. Nasals shorter than the frontal, more than twice as long as the suture between the prefrontals. Prefrontals usually in contact with the second upper labial. Frontal more long than broad, as long as its distance from the rostral or the tip of the snout. One preocular and two postoculars. Two superposed anterior temporals. Seven or eight upper labials; third, fourth, and usually fifth entering the eye. Both pairs of chin-shields in contact, or posterior pair separated by one scale. Body long. Dorsal scales subimbricate, keeled or with two or three tubercles, in 39-45 rows (27-33 anteriorly). Ventrals 281–385, smooth or with two or more tubercles. Greenish-olive above, with blackish or olive transverse bars or annuli, broadest on the back, sometimes connected by a black band along the belly; or yellowish, with a black vertebral band and a few black bars on the neck. Length of head and body 1,360 mm (54 in); tail 140 mm (5.5 in). In a 2019 study it has been found it uses a complex system of blood vessels in its head called, the Modified Cephalic Vascular Network (MCVN) which is an adaptation that helps provide the brain with extra oxygen from water when submerged.

Found in the Indian Ocean (From the Persian Gulf, Iran, Pakistan, India, Sri Lanka, Bangladesh, Myanmar, Thailand, Malaysia, Philippines: Visayan Sea, Panay) and the marine waters around Korea, Japan, Solomon Islands, South China Sea (including Hainan), East China Sea (including Taiwan), coastal regions of Shandong and Liaoning (China) coasts of Persian Gulf (Oman, United Arab Emirates), east through South Asia until New Guinea. It is also reported from Brunei

Hydrophis cyanocinctus inhabits shallow coastal waters. It is often accidentally caught by prawn trawlers.