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.

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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:

• Here’s a very large picture of the tongue-replacement isopod, Cymothoa exigua, mentioned above.
• Here’s an article about the Giant Isopod, Bathynomus giganteus.
• Incidentally, in another group of crustaceans, the Remipedia, there’s a family called Godzillidae.