Hi James,
Can’t be certain, as microscopy would be needed to be sure, but they have the general looks of Physarum album.
Pretty common, and can appear on all sorts of herbaceous/leafy/mossy/very rotten wood debris types of substrates: –

[attachment=2]Physarum album 01a 051111.jpg[/attachment]

[attachment=1]Physarum album 02b 100412.jpg[/attachment]

[attachment=0]Physarum album 02a 160212.jpg[/attachment]
Regards,
Mike.