Hi I found hundreds of these creatures washed up on the shore of Pankor Island Malaysia the other day. The reminded me of a ragworm but were different. I'm not sure if the emerged from the sand or were washed up by the sea. They were about 2 inches in length until they stretched themselves while attempting to walk/swim back into the water then they extended to about 2.75 inches.
Thanks bombuslucorum for putting me on the right track. Do you have any idea if they might have crawled out of the sand, or been washed up by the tide? There were literally thousands of them all along the water mark. I wondered if this was a nightly event or just a one off. Unfortunately I was only there for one night, so I couldn't check myself. There had been no rough weather or heavy sea state.