Slender-necked Sea Snake (Hydrophis melanocephalus) is also known as a Black Headed Sea Snake. There is a bit of variation in most of the sea snakes. They look a lot alike and good information is hard to find. This snake seems to fit the name above. Amami
Same snake as the one above it. Long with a very slender neck. Amami
Slender-necked Sea Snake (Hydrophis coggeri) this snake is also long with a slender neck. The body has more distinct white markings and the head less black with a white blotch behind the eye. It looks just like snakes described as (Hydrophis coggeri). All the descriptions describe the range as around Autralia and the South Pacific. This was taken at Amami. Trying to identify sea snakes is a little frustrating. If anyone knows for sure what these are let me know.