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.
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