Tuesday, February 17, 2009
Well I am not quite sure how this happened but we are up to the letter 'E' in ABC Wednesday already. Where does the time go?
This week I am going with E is for Exuvia. An exuvia is the shed exoskeleton of an arthropod, arachnid or crustacean. Sometimes it is the adult form that has just grown larger. Like Harriet our Tarantula, this is an old exuvia of hers from about two years ago.
When she sheds she flips upside down, splits the back and pulls all her legs out from the old shell, here you can see the openings where her legs were.
Crustaceans too will shed as they grow, like our Devil crayfish. This exuvia was soft and the same muddy bluish/gray as the crayfish when it was first shed but after a couple of hours out of the water it hardened and turned to this bright orange colour.
Our hermit crabs shed from time to time too although I must be careful not to remove the exuvia because after they have shed it, they have to eat it to reabsorb the calcium. This helps the new exoskeleton to harden properly.
Another time an exuvia is produced is when an organism is transforming between life stages. This dragonfly nymph would have lived under water for many months before eventually climbing up a twig or reed, out of the water and emerging into the adult dragonfly form, leaving the nymph exuvia still gripped firmly onto the stem.
There is some question as to whether the term relates to the shed skins of reptiles like snakes, it seems to depend who you ask! Certainly it is far less widely used with reference to herps than it is with inverts but strictly speaking I suppose it is not incorrect. What do you think?
For many great posts on or about the letter 'E' go to ABC Wednesday and travel the blogosphere!
Photo Credits - CJT
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