Trilobites are not isopods

Prof. PZ Myers at Pharyngula attended a talk by Kent Hovind at a U.S. college, Cloud State University. Among other things, Dr. Myers had this to say:

And the lies were just so painfully blatant: as an example, he claimed that trilobites weren’t old and they weren’t extinct, and to ‘prove’ his claim, he showed a picture of an arctic isopod and announced that there it was, alive and crawling, proof that the biology professors have all been lying to you.

My comments:
Young-earth creationist Kent Hovind includes in his talks an assertion that trilobites are still around because he has—ta-da!—a picture of an isopod. That’s like saying that horseshoe crabs live in the Prairies because you found a grasshopper. But “Dr.” Hovind seems unaware of his mistake. It’s almost as if Hovind’s attitude towards God’s creations is, “If you’ve seen one bug, you’ve seen them all.” Is it a lie if you don’t care?Isopods are only distantly related to trilobites. Allow me to introduce Hovind to the Tree of life page for arthropods.

The further apart the names are in the list, the more distantly related they are. Trilobites are distinguished by the three lengthwise sections of the body. (Harvard University shows a nice selection of trilobite species.) They are also extinct, as shown by the little dagger beside their name. I know of no living crustaceans with bodies divided into three lengthwise lobes. Here is a fossil of a trilobite:
Here is an isopod:

You’ve seen them, because sowbugs and pillbugs are isopods. Sowbugs and pillbugs are those little, segmented grey bugs that hide in damp places. Pillbugs curl into a ball when you pick them up; sowbugs just run away. I remember learning in school that they are crustaceans and breathe with gills, so they must live around moisture.

Both trilobites and isopods are in class Arthropoda (“jointed legs”). To call them the same is like saying or that a clam is the same as an octopus. (Both are in class Mollusca.) To find the isopod branch of the arthropod tree, click on Crustacea, then Malacostraca, then Peracarida, then Isopoda. (The middle picture on the Isopod page shows a parasite that enters the mouth of a fish, then eats the tongue and lives in its place.)

But what is Hovind’s point? Even if an old form persists, “cousin” groups could still have evolved from their common ancestors, and evolutionary pressures continue to operate today. Is it simply a chance for him to laugh at the foolish scientists who can tell the difference between a crustacean or a trilobite? Besides being a cheap shot, it’s a remarkably useless one.

More links:


15 Responses to “Trilobites are not isopods”

  1. Walter Brameld IV Says:

    Regarding the arthropod taxonomy picture from the Tree of Life site:

    “The further apart the names are in the list, the more distantly related they are.”

    I probably don’t know how to read the taxonomy chart so please correct me if I’m wrong, but it seems to me that the four main branches in that tree are sibling branches. If that is the case, then couldn’t they be reordered so that the branch leading to trilobites comes immediately after the branch leading to hexapoda and crustacea, without changing the meaning?

  2. monado Says:

    The four groups are, I believe, subphyla. Exactly how they are related is still being worked out. But isopods are four levels down in Crustacea, so in that sense they are distant.

    However, I believe that current thinking puts chelicerates and trilobites in one group and crustaceans in another.

    This might help: Arthropod cladogram, which comes from Arthropoda.

    But even if they are “only” in different phyla, that is like confusing a vertebrate with a tunicate. No one who cared enough to open a high-school textbook would make that mistake.

    Thanks for the comment! I had fun looking for arthropods on the Web.

  3. monado Says:

    Oops! I meant “different subphyla.”

  4. Anonymous Says:

    Isopods-a sowbug does not roll up, but a pillbug does roll up. They are both isopods.

  5. monado Says:

    Thanks for the correction. That’s what I get for relying on my Grade 9 Biology, where they told me a sowbug was the proper name for a pillbug.

  6. Stanton Says:

    Forgive my late commenting, but, a pillbug is a different genus of isopod than a sowbug…
    The former rolls up into a pill-like sphere, while the latter can not, and has tail-like cerci.

  7. monado Says:

    Thanks for the correction. I’ve fixed it. I thought their behavior just depended on the mood they were in.

  8. How to catch giant isopods « Science Notes Says:

    […] is cute, but as we all know, trilobites are not isopods. Posted in humor, science. Tags: biology, evolution, invertebrates, […]

  9. spencer Says:

    uh. a pillbug and many similar living species are the closest things to trilobites alive from a morphological point of view. they represent a very basal bug form regardless if there are other closer relatives to the trilobite that have derived significantly.

  10. Hmmmm Says:

    Again… Trilobites are extinct, BUT Trilobites and Isopods are still the same kind of things. different species, but they both came from a “common” ancestor. That was his point.

  11. monado Says:

    They are sister groups in the arthropod clade–organisms with jointed legs, as their name states, because they have external skeletons. But to say that trilobites are the same as isopods is the same as saying that spiders are millipedes, scorpions are water fleas, or barnacles are butterflies. The trilobites are extinct. Hovind’s point was that trilobites are not extinct. He is wrong.

    Incidentally, Hovind’s “doctoral dissertation” for Patriot Bible “University” is up on the web. Take a look: I doubt it would get a “C” as a term paper for a Grade 9 student. (Hat tip to Dispatches from the Culture Wars.”

  12. starspawn Says:

    It’s already shown that insects are a side-branch within crustaceans.

    So what is it that makes trilobites more distant to crustaceans than insects ?

    anyone can tell me ?

  13. Wade Nevin Says:

    The post above says:

    Trilobites are distinguished by the three lengthwise sections of the body

    I looked up these three sections of the trilobite:
    Head Body/Thorax Tail/Abdomen

    The SAME 3 lengthwise segments of the isopod.

    Other than that one point, he does not distinguish the isopod or the trilobite in any biological manner. This makes me think the isopod is a modern trilobite if there is nothing biological to distinguish the 2.

  14. monado Says:

    I’m impressed that not only did you fail to read the chart, which clearly shows that isopods, spiders, and butterflies are equally distant from trilobites; you also don’t understand what “lengthwise” means. The three lengthwise lobes of a trilobite are left, centre, right. Meanwhile, an isopod has a cephalothorax, which is a head fused with the first thoracic segment; then two to nine thoracic segments; then about six abdomen segments; and finally tail segments. It’s not exactly the classic crosswise division into head, thorax, and abdomen, although you can find it over-simplified to such in lessons for fourth-graders

  15. John Miller Says:

    What came first the chicken or the egg. My question is how did the giant isopod evolved ?

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