While reading the latest National Geographic mazagine this month, this ancient and evolution-proof creature is written about again. By ancient, I am refering to 450 millions back then, even long before dinosauers came ruling the earth. How could we not be interested by this very organism, which has happened to survice through all the major extinction events, and presenting themselves in the form almost unchanged all these years?
But what amazes is not its age, not its alienoid appearance, not its close relationship with spider and scorpion (ITS NOT A CRAB!), but its blood.
I remember once in Cheung Chau, passing by a seafood restaurant, I encountered a chef preparing a horseshoe crab dish (probably a soup). Flashing back the memory, I didn't see any blood as he chopped the shell into half, at that time I thought: nah its like crab - bloodless.
Now with the magazine in hand, I was shocked. For God's sake, not only does it has blood running inside, it is blue in color!
The peculiar blood color is due to their copper-rich content, instead of hemoglobin in human, they had with them hemocyanin that carry oxygen for them. The blue blood not only charms with its color, but its medical value as well. Amazingly, in these bottles of blue fluid, there runs a type of cell known as amebocytes (literally means: a cell that can changes its shape), which have a special power - they react with the tiniest amount of bacteria in the surrounding and clot the blood. In vivo, these cells act as a defense mechanism for crabs, so that when there is a small leak of seawater into its blood, the breakpoint will seal immediately, stopping bacteria entering its body. Indeed, perhaps it is this unique immune power that makes this creature a living fossil.
And scientists use this very property as a bacterial screen for sterile materials, and help us detect the trival number of bugs, which is exceedingly important for immunodeficient patient. On further readup on the web, once the blue blood was also brought up to the space, to check for possible live-forms outside the earth!
Sadly though, due to recent enviromental over-exploitation, this seemingly-everlasting organisms are reducing in number drastically in recent years. Surviving previous extincting events didn't make it through this one - the human damage. Perhaps, someday later, our grandsons and daughter can only see this lovely creature on fossils, where the sky-blue blood can never and no longer be appreciated.
Its sad, but true.
