Placement of worms, leeches and similar beings beyond kingdom

Can anyone give pointers for how to place intertidal worms and leeches beyond kingdom?

Atm I think I understand what a planarian looks like… and inland, an earthworm is obvious… … otherwise I’m pretty lost on where to place these sort of observations… at the level of phylum there are a lot of different options with worm as the common name.

I think most bristly worms can be placed in

Edit: and I guess they’re in Phylum Annelida, which I think most segmented worms can be put in. But I’m definitely no worm expert.

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Thanks! Yes…the bristly Polychaeta I see do look simpler… though I also found this one this week which is also Polychaeta but not bristly!

I wondered how literally I should take the name segmented worms in terms of placement so that’s good to know. I will be more confident in placing ones with segments there.

But yes, I guess more confusing are the leechy creatures like this or non-segmented worms like this or this…autosuggest just arbitrarily throws up Potworms for most of them no matter what it seems …

For the first, consider “The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a class containing about 162 species of unsegmented marine annelid worms.” – Wikipedia.

For the others, I’m curious. I’ve seen those before but have no idea what they are.

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There’s a fairly decent non-technical guide to the 31 invertebrate phyla here:
It has pictures of representative species and a general description of ecology and where they’re likely to be found (e.g., parasites, marine, terrestrial, …). And yes, a lot of them have “worm” in their common name even though they are not what we may think of as “worms.”


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.