[From many - one.]

"...one question why do some organisms never evolve??
even though they are under conditions that have changed over multimillions of years (green algae)- even large animals such as crocks-sharks seem hardly changed??"

several answers

1. they may not change in appearance but may have many metabolic changes

2. the evolved versions and the old versions may co-exist

2 they may be prevectrly siuted to their environment

[ConsentofGoverned]

yes you have listed some ideas but does it not bother you that evolution seems to skip many species ..from the very beginning of life on earth?? what makes these species resistant to the dynamic forces we use to explain evolution?? I don't know but many experts posting here also do not (but will not admit it) ..

ID would say if there is no need in the plan for a species to be changed it will remain unchanged even after a billion years go by.