Two species of sea urchins live practically side-by-side in sandy bottoms. The two species appear to have the same diet: drift seaweeds and other bits of organic matter. They can live in the same environment without competing.
As it compels them to live in the same environmental surroundings so the characteristics of living nature also get developed as their current following situation that's helping them to get the same food & habitat.
I am going to go with steroids because they are a type of lipid.
A flagella helps an animal sperm move!
