Scorpions vs. Crayfish

[David Stuchkus]

     My name is Steve Byrd and I am a laboratory assistant at Clayton
State College in Morrow, GA.  While researching in preparation of a
comparative anatomy lab, I noticed an interesting difference between
the crayfish and scorpion.

    Both of these creatures have opposable "thumbs" on their chela.
However, the opposable "thumb" on the crayfish is medial where the
scorpion's is lateral.

    If anyone has any idea as to what caused this evolutionary
difference, I would by interested in hearing them.

    Please respond to:

stuchkus at gg.csc.peachnet.edu

Thanks in advance,
Steve B.
Clayton State College