A reef is a ridge of a rock of any type of land that extends some distance just under the surface of the water. A coral reef is a lot of calcium carbonate that is also made up of living creatures. A coral reef is created when a small amount of dead coral turns into calcium carbonate. This process is very slow. The famous reefs are the Great barrier Reef of Austria and Belize and Cayman Islands. Wave actions are usually not a problem due to hard coral reefs. The reef reduces a wave energy. But sometimes waves can break off or flatten large portions of coral reefs, forming grooves in once circular reef. The higher areas between the grooves are known as buttresses and may grow together at the top producing arches. Answer: Landform that develops on coral reefs as a result of wave action are Arches.
Based on the scenario being described within the question it can be said that the most likely reason for this misconception would be that the spiral galaxies looked like clouds of gas and dust through telescopes because of their distance from Earth. During that time telescopes were still not as advanced and could only see so much, nowadays they are much more advanced and these galaxies are being analyzed and understood more clearly.
