Spiny Orbweaver

"Spiny orb-weavers is a common name for Gasteracantha, a genus of spiders. They are also commonly called Spiny-backed orb-weavers, due to the prominent spines on their abdomen (cf. genus Isoxya). These spiders can reach sizes of up to 30mm in diameter (measured from spike to spike). Although their shell is shaped like a crab shell with spikes, it is not to be confused with a crab spider."
Ref: http://en.wikipedia.org/wiki/Spiny_orb-weaver

Ref:http://en.wikipedia.org/wiki/Spiny_orb-weaver