The specific epithet tenuis ("slender") refers to the snake's appearance.

[2] The species grows to an average of about 130 cm in length.

It is long and slim, with a small brown head and a pale body.

[2] The snake is found in marine waters off the north-west coast of Western Australia, from near Dampier to Broome, and in the Arafura Sea.

The type locality is Cape Jaubert, near Broome.