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.
They argue that the Great Depression was caused by the banking crisis that caused 1/3 of all banks to vanish, a reduction of bank shareholder wealth and more importantly monetary contraction by 35%. This caused a price drop by 33% (Deflation).