Thats very helpful, thanks!
In addition to existing iNat data, it’s given me a starting point.
For anyone else who is trying to figure this out down the line :
In summary :
Annelida - segmented + worm OR leech-shaped
Nematoda - non-segmented + worm-shaped
Platyhelminthes - non-segmented + leech-shaped
Best to place obs like these into these common larger groups I think.
The delineations are overly simplistic and there are clearly exceptions but better than trapping them at Kingdom level.
In more detail for now :
Most non-microscopic worm-like beings will belong to Annelida ( Segmented worms - 160000 obs) with segmentation being the delineating feature as @tiwane said.
If no segments visible, most obs belong to Nematoda (Nematodes - 5000 obs) or Nematomorpha ( Horsehair worms - 2800 obs ) but the latter look visually distinct ( extremely long and thin ) and their habitat is freshwater.
Most non-segmented leech-like beings seem to be Platyhelminthes (Flatworms - 46000 obs ) or Nemertea (Ribbon worms - 3700 obs). Not sure how to delineate these groups but I guess better to just place in Flatworms and await correction than leave at kingdom. (Actual leeches belong in Annelida though!.. as they have visible segments)
Beyond that the other worm-named phyla are not so commonly observed :
541 observations :
Phoronida ( Horseshoe worms ) - confusing common name! not very worm-like.
237 observations :
Hemichordata ( Acorn worms ) - existing obs look like the kind of thing one might well find in tidal zone, so not sure why there are so few obs of this. Not sure how to delineate these.
114 observations :
Chaetognatha (Arrow worms ) are marine. Existing obs are almost all translucent.
48 observations :
Acanthocephala ( Thorny-headed worms ) - existing obs seem to be almost exclusively parasites on Amphipods.
28 observations :
Priapulida ( Priapulid worms aka penis worms ) - relatively large, phallic in shape and distinctively patterned skin
Then only in southern hemisphere it seems :
1600 obs :
Onychophora (Velvet worms) - but they have lots of legs so are v distinctive
Sipuncula ( Peanut worms - 1250 obs ) are mentioned by both @sedgequeen and the article as being unsegmented. They fall under the phylum Annelida (segmented worms) in iNat taxonomy though for some reason …so this may be a source of confusion when placing. However, most obs seem to have a distinctive peanut-like patternation to the skin.