sea snake
Refers to true sea snakes (Hydrophiinae), venomous marine reptiles found in warm coastal waters.
I saw a sea snake in the sea off Okinawa.
worm eel; snake eel
Refers to eels of the family Ophichthidae, which resemble snakes but are fish. Often encountered by divers and fishermen.
The snake eel that buries itself in the sand is actually a type of fish.
yellow-bellied sea snake; pelagic sea snake
slender-necked sea snake; Hydrophis melanocephalus
Katakana spelling is the most common written form for this word.
Kanji spelling is understandable but the word is usually written in kana.
Hiragana spelling is also used, though katakana is more typical for animal names.
Compound of 海 (umi, 'sea') and 蛇 (hebi, 'snake'). The katakana spelling is standard for biological names.