Cnidaria is a phylum within Kingdom Animalia which consists of hydras, jellies (or jellyfish), sea anemones, and corals. All cnidarians are radially symmetrical, and there are two main radially symmetrical body types.
The stock market crash, on black Tuesday (October 29, 1929) began the Great Depression.
The only near consensus is on the question of what triggered the not-quite-a-depression. In 2007, the housing bubble burst, leading to a high rate of defaults on subprime mortgages. Exposure to bad mortgages doomed Bear Stearns in March 2008, then led to a banking crisis that fall. A global recession became inevitable once the government decided not to rescue Lehman Bros. from default in September 2008.