This one appears to be the widespread Ptychodera flava. The worms tend to be small, usually 150mm or less when exposed, with thin skins through which you can easily see the sand particles that they are passing through their guts. These are abundant in some lagoon sand flats, such as the sand spits near South Loi, North Loi and Gugeegue Islands. While there is generally no visible indication of their presence, sweeping the top layer of sand away will often reveal many individuals. But they do not appear to leave the spaghetti-like mounds on the surface of the sand.
We presume, but are not sure, that the white ones below are a color form of Ptychodera flava.
Created 16 February 2019
Updated 27 April 2021