Taken in Sai Kung West Country Park.
I know very little about Annelids, but after quite a bit of web searching my best guess is that it is an Amynthas earthworm of some kind. From some descriptions A. aspergillum or A robustus seem to be best possibilities?
This worm was about 30 cm long and thick, about 2cm in diameter. It was a shiny pearl colouration. I'd love to know what it is.