except in environments, like the mud of the ocean floor, where the conditions don't change much.
The coelacanth - the fish in question which has remained unchanged for 380 million years does not live on the ocean floor. Further, the environment comprises not just the physical environment of weather and habitat, but competing species. Are you going to assert that no new species evolved during the 380 million years in which the coelacanth has been around in the ocean???????????????