Hydrophis cyanocinctus, commonly called the annulated sea snake or the blue-banded sea snake, is a species of venomous sea snake in the family Elapidae.
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 1360 mm; tail 140 mm.
Found in the Indian Ocean (From the Persian Gulf, Iran, Pakistan, India, Sri Lanka, Bangladesh, Myanmar, Thailand, Malaysia, Philippines: Visayan Sea, Panay, etc.) 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.
Hydrophis cyanocinctus inhabits shallow coastal waters. It is often accidentally caught by prawn trawlers.
It feeds on marine invertebrates and also on various groups of fish such as eels and gobies.
This species is ovoviviparous. The young are born alive in broods of 3-16. The newborns are about 38 centimetres (15 in) long.