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 causes of the Great Depression in the early 20th Century are a matter of active debate among economists, and are part of the larger debate about economic crisis, although the common belief is that the Great Depression was triggered by the 1929 crash of the stock market.