The first echinoderms evolved on our planet about 520 million years ago, long before the first dinosaurs.
Some of them are considered harmful species. Sea stars of the crown of thorns species, for example, destroy corals, and their active reproduction in general threatens them with complete extinction. One adult crown of thorns (by the way, they are very poisonous) can destroy up to 10-20 sq. feet (1.5-2 m²) of corals per day, absorbing the necessary nutrients from them.
Most echinoderms have shrunk in comparison to their ancestors over hundreds of millions of years of evolution, but otherwise have not changed at all.
Some of their species are vital for the ecology of the world’s oceans. Sea cucumbers constantly sift through the bottom sand and absorb dead organic matter from it.
Echinoderms cannot control the composition of their body’s saline fluids, and therefore any change in the salinity of water is deadly for them.