Thai National Parks

Species of Thailand

Dwarf sea snake

Hydrophis caerulescens, George Shaw, 1802

(In Thai: งูแสมรังลายเยื้อง, ngu saem rang lai yeuang)

Hydrophis caerulescens, commonly known as the dwarf sea snake, is a species of venomous sea snake in the family Elapidae.

Geographic range

Indian Ocean (Pakistan, India, Bangladesh, Myanmar (Burma), Thailand, W Indonesia, Malaysia), Coasts of Shandong and Guangdong (China), South China Sea, Australia (Queensland), New Caledonia/Loyalty Islands.


The dwarf sea snake is bluish or grayish blue dorsally, merging to yellowish ventrally, with 35-58 deep bluish-black crossbands. The crossbands are as wide or wider than the interspaces, well defined in younger specimens, but obscure in older specimens. The head is black, and in juveniles may also have a yellowish horseshoe-shaped mark.

Adults may attain a total length of 74 cm (2 ft 5 in).

The dorsal scales are arranged in 38-54 rows at midbody (31-43 rows on the neck). Ventrals 253-334.

Each hollow poison fang is followed by a series of 14-18 solid maxillary teeth. The dorsal scales on the thickest part of the body are quadrangular or hexagonal in shape, feebly imbricate (overlapping) or juxtaposed. The ventrals are almost twice as large as the adjacent body scales.

Head very small. Anterior part of body very slender, its diameter about one third the diameter of the posterior part. Rostral broader than deep. Frontal longer than broad, shorter than its distance from the rostral, much shorter than the parietals. One preocular, and one post ocular. Two superposed anterior temporals. Seven upper labials, the third and fourth entering the eye. Chin shields very small, the posterior pair separated by scales. Ventrals distinct throughout the entire body length.

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Scientific classification

Hydrophis caerulescens

Common names

  • English:
    • Dwarf sea snake
    • Dark blue-banded sea snake
  • Thai: งูแสมรังลายเยื้อง, ngu saem rang lai yeuang


  • Hydrophis caerulescens caerulescens, George Shaw, 1802

  • Hydrophis caerulescens hybridus, Hermann Schlegel, 1844


  • Polyodontognathus caerulescens, Tanya Chan-Ard et al. (2015)
  • Polyodontognathus caerulescens, Van Stanley Bartholomew Wallach et al. (2014)
  • Hydrophis caerulescens, K.L. Sanders et al. (2012)
  • Hydrophis caerulescens, Arne Redsted Rasmussen et al. (2011)
  • Hydrophis caerulescens, Nguyen Van Sang et al. (2009)
  • Polyodontognathus caerulescens hybridus, Vladimir Emelyanovich Kharin (2005)
  • Polyodontognathus caerulescens, Vladimir Emelyanovich Kharin (2005)
  • Hydrophis caerulescens, Patrick David et al. (2004)
  • Polyodontognathus caerulescens, Vladimir Emelyanovich Kharin (2004)
  • Hydrophis caerulescens, Harold Cogger (2000)

Conservation status

Least Concern (IUCN3.1)

Least Concern (IUCN3.1)


No photo for this species yet

Range Map

Distribution map of Dwarf sea snake, Hydrophis caerulescens in Thailand
  • Bangkok Coast
  • Narathiwat Coast
  • Phuket Coast
  • Ranong Coast
  • Samut Prakan Coast
  • Satun Coast
  • Surat Thani Coast
Range map of Hydrophis caerulescens in Thailand