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 immediate cause of the Great Depression of the 1930's was the catastrophic collapse of investment purchases. There were prior causes, such as the real interest rate stemming from restrictive monetary policy, but it is in investment purchases that these factors have their effect.