COELOM.

One benefit of copyediting specialized material is that you learn new words. Taking my first glance at a new article about coelomic effusion in frogs (exciting, I know), I immediately wanted to know what coelomic meant. It certainly looked like it came ultimately from Greek κοιλος [koilos] ‘hollow,’ but that was pretty vague. So I went to the dictionary. It’s the adjective of coelom (SEE-lum), which Merriam-Webster said is “the usually epithelium-lined space between the body wall and the digestive tract of metazoans above the lower worms,” which told me basically nothing. The New Oxford American Dictionary said “the body cavity in metazoans, located between the intestinal canal and the body wall,” which was better, except that I had no idea what a metazoan was. M-W: “any of a group (Metazoa) that comprises all animals having the body composed of cells differentiated into tissues and organs and usually a digestive cavity lined with specialized cells.” No good whatever. NOAD: “Metazoa a major division of the animal kingdom that comprises all animals other than protozoans and sponges.” Much better; everybody and his dog is a metazoan. We see the virtues of NOAD’s “core sense” system—M-W’s definitions are absolutely accurate but sometimes make no sense to the average user, whereas NOAD’s are written with the nonspecialist in mind; if more specifics are needed, they are given after the core sense (here, “they are multicellular animals with differentiated tissues”).
I decided to see how other major dictionaries handle coelom. The OED says “The body-cavity of a cœlomate animal,” which is both good (“body cavity” is clear) and bad (what’s a “cœlomate animal”? why, it’s one “having a cœlome or body-cavity distinct from the intestinal cavity; belonging to the Cœlomata“—gee, thanks a heap!). But the American Heritage hits the jackpot:

The cavity within the body of all animals higher than the coelenterates and certain primitive worms, formed by the splitting of the embryonic mesoderm into two layers. In mammals it forms the peritoneal, pleural, and pericardial cavities. Also called body cavity.

It uses some fancy words, but the meaning is clear: it’s the body cavity in higher animals. Well done, AHD!
And now, back to the frogs…

Comments

  1. What do you find wrong with the OED entry you say “gee thanks” at? I mean “body-cavity” is clear, and it’s how _you_ explain it in your summation of the AHD …

  2. It’s the body cavity of a coelomate animal, and that phrase is not usefully defined.

  3. dungbeetle says:

    “body cavity of a coelomate animal” ’tis simple, it be the cavity of an animal that has a body cavity.[coele Gr Koilia body cavity a chamber]. like “win a victory”

  4. Michael Farris says:

    I loves the American Heritage Dictionary.

  5. I think this is very subjective; I was quite happy with Merriam Webster’s definition of “metazoan,” for example. I don’t think it takes much special-ist* knowledge to know that even jellyfish, one of the most basic species of animals, have differentiated tissues and organs.
    *Pardon the hyphen. Apparently the string C-I-A-L-I-S is not allowed in comments.

  6. I don’t think it takes much special-ist knowledge to know that even jellyfish, one of the most basic species of animals, have differentiated tissues and organs.
    We’ll have to agree to disagree. I think the vast majority of dictionary users would not find that definition of much use. (I apologize for the obstacle course presented by my spam blocker!)

  7. I’m thinking that in high-school biology kids should memorize the following tree:

    Life
    prokaryotes (bacteria and stuff)
    eukaryotes (made of fancy cells with nuclei)
    a couple of dozen groups of single-celled things
    plants
    fungi/metazoan group (multicelled eating things)
    fungi (includes molds and mushrooms)
    metazoa ("animals")
    a few lower groups
    sponges
    higher animals
    a couple of minor groups
    bilaterally symmetric animals
    without body cavity
    with body cavity
    

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