TODAY I WAS reading about protostomes and deuterostomes, and in the process stumbled across a mention of chaetognaths as deuterostome-like protostomes. Since I had no clue what a chaetognath is, I looked it up and found Wikipedia’s entry, which describes them as “predatory marine worms”. This prompted the question: What is a worm?

I know it may seem shocking, but I haven’t really given much thought to the essence of wormness since General Zoology in college. So since I was already at Wikipedia, it was convenient to look up their article on worms. I found it wasn’t very illuminating. It lists multiple phyla containing “worms”, whimsically wrapping up the list with “Tapeworm {live in humans}”, which just goes to show you should double-check anything you find on Wikipedia. So I did so–and found “worm” really has no practical meaning at all.

This time I decided to go somewhere authoritative, so I jumped over to the Tree of Life’s page on Bilateria. There I see several groups of “worms” as unrooted clades, more “worms” in Lophotrochozoa (including Annelida, which contains the familiar earthworms), and other “worms” in the sister group Ecdysozoa (one being the Priapulida, which upon further research Terry Pratchett would classify as “humorously-shaped ecdysozoans”). It’s clear that many “worms” are not particularly closely related to each other, but at least so far they’re all protostomes. Shall we say a worm is a soft-bodied, elongated, limbless protostome? Just on a hunch I clicked over to expand the deuterostomes, which I found contain more “worms”! Apparently the word “worm” simply means “a squiggly bilaterian”, and thus is about as useful as the word “bug” in the vernacular, where it means “a crawly bilaterian”.

Based upon this research I propose an abolition of the word “worm” as a descriptor of any animal group and its replacement by “vermiform”, or perhaps “worm-like” for a more general audience. Since most people will think of the earthworm as the iconic worm, this terminology should communicate that it’s a squiggly bilaterian without suggesting a close evolutionary relationship of all “worms”.

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