Mucilago crustacea goes through a white plasmodial stage and is generally associated in grassy areas rather than on chip mulch. Are you able to revisit this today or tomorrow to observe the mature stage? We we last saw some similar to this it took five days to mature before we could positively say it was a Fuligo species, most probably F. septica; its impossible to be 100% certain without microscopic examination, perhaps you can do some micros or collect and lodge at the herbarium.
Thanks so much for your comments @Teresa . Unfortunately I wasn't able to head back to gather further observations. Will keep your helpful comments in mind for next time I come across slime mould though!