Neptune satellite (6)
I believe the answer is:
triton
'neptune satellite' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for triton that I've seen before include "Greek sea-god like man with fish's tail, trident and shelltrumpet" , "conch-blowing deity" , "Moon" , "Son of Poseidon, shown as man with fish's tail with trident and shell-trumpet" , "Greek minor sea-god with trident, fish-tail and shell trumpet" .)