This spider is very unique and completely different to the ones I have seen so far. It looks like a hermit crab. The spider was guarding its nest and perfectly camouflaged. If anyone can ID it , will be great.
I wonder if it could be a species of Poltys. The posture with legs drawn up around the carapace, along with the bizarre shaped abdomen would fit this genus. See, for example: http://www.findaspider.org.au/find/spiders/142.htm and http://www.arachne.org.au/_dbase_upl/Araneidae_Poltys_Smith1465_complete.pdf