On Sat, 10 May 2003 18:58:44 +0000 (UTC), "Robert Karl Stonjek"
 wrote:

>I'm wondering if anyone knows anything interesting about the evolution
>of blue blood?
>
>As you all no doubt know, rusty blood is red (from iron oxide) and blue
>blood occurs because the oxygen carrying component in the blood is
>copper.
>
>The Horseshoe crab is the best known blue blood, but what of others?
>And if the Horseshoe crab had Blue Blood, does this mean that other
>ancient animals such as trilobites might also have been blue blooded?
>
>I'll be interested to hear any comments on Blue Blood (thoughts of
>"knowing the basics" were severely dashed when my complete ignorance of
>blue blood was revealed during a "coffee table" television documentary.
>Fortunately, no-one was around to witness my feebleness of knowledge
>about Horseshoe crabs and their Blue Blood).

There are a variety of oxygen carrying compounds in the blood of
different organisms.  The four major ones are 
  Hemoglobin: 
      protein with heme group binding iron,  
      found in the vertebrates and scattered also among annelids, 
      arthropods, and molluscs
      red when oxygenated, bluish when deoxygenated
  Hemocyanin: 
      protein binding copper, 
      found in arthropods and molluscs
      blue when oxygenated, clear when deoxygenated
  Chlorocruorin: 
      protein with heme group binding iron
      found in annelids
      green when oxygenated, clear when deoxygenated
  Hemerythrin:
      protein directly binding iron with no heme
      found in annelids
      violet-pink when oxygenated, clear when deoxygenated
See 
http://webusers.xula.edu/cdoumen/CAP/RespPigm1.html
or
http://www.j-bradford-delong.net/movable_type/archives/000566.html
or
http://www.wikipedia.org/wiki/Blood
and many other sites (search "respiratory pigments")

I don't have any good references (or any information at all, for that
matter) on why hemoglobin should be so widespread or why annelids
should be so diverse. Can anyone help out here?
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