Evolution:
Evolved before annelids and arthropods diverged?
The two pictures on the top show
Jaw of Polychaete worm, Nereis virens while the two pictures on the bottom show
Sting of scorpion Vaejovis confusus.
In both organisms: Ca is present in Mn region, and Cl in Zn region.
Evidence for early evolution:
- Widespread phylogenetic distribution (more than ½ of examined species), with repeated element patterns (distal Zn and Cl, proximal Mn and Ca).
- Similar ultrastructure (e.g. nano-canals) in examined chelicerates and insects
- Time course of Zn incorporation is similar in the examined chelicerate and insect, beginning roughly 150 hrs. after pre- ecdysial tanning and lasting about 100 hours. Time course for Mn and Cl incorporation also similar (Mn before Zn, Cl with Zn).