Friday, October 28, 2011

New Suit of Armour


The trouble with being an invertebrate with a hard external skeleton is that you have to change your suit of armour every time you grow a little bigger - which is what this woodlouse is doing. It's a risky business, leaving you exposed to predators until your new exoskeleton hardens, so this cautious crustacean is doing it in two stages. It's already slipped out of the rear half and its new shell plates have become hard and shiny. Now it's extricating itself from the head end, and here you can see that the newly exposed shell plates are still soft, with a dull surface. The animal hasn't quite removed its delicate, all-important antennae from inside their armour yet - if you double-click the image to enlarge you can just make them out inside their old translucent covering. 

This woodlouse is Oniscus asellus and you can find more about its biology here

The whole process is known as ecdysis and all invertebrates that shed their old armour in this way are grouped together as ecdysozoans. You can read all about it here.

6 comments:

  1. I really enjoyed this..........superb photograph. The microscope images are even better. How do you keep it still? Pop it in alcohol?

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  2. Hi Adrian, Just cooled it down a bit (several times - they recover quite quickly) in the fridge (while the wife wasn't looking!).Still got a lot of blurred images though...

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  3. That's what I do for macro.......I then get the beetle out after twenty minutes and pop it on a big leaf. Hopeless it is. I just get all set up and off they trot. The Stag Beetle I found earlier this year escaped in the fridge.....I never have located it......still feel a little guilty as they are rare in Derbyshire. I look at some of the focus stacked images and they have to be both dead and Superglued.

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  4. I've had accidents like that Adrian. I once put a New Zealand flatworm in the fridge in a screw-topped jar without realising that these worms are the Houdinis of the animal world and can crawl around screw threads. I was in the doghouse for some time after that - and we never found the flatworm...

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  5. I was going to comment on the woodlouse but the idea of a New Zealand flatworm wandering in your fridge has put any other thoughts right out of my head! That and Adrian's beetle.

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  6. Hi Toffeeapple, it isn't a pleasant thought, I have to admit...

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