"First, it's misleading to say that the lampreys "haven't evolved". Some of their descendants have a very similar shape to their remote ancestors, that's all you can say. Those descendants may well have changed in many ways that aren't reflected in their morphology, but morphology is all that the fossil record preserves."
I don't know...that sounds pretty weak. Concerning the many changes you speculated about, what kind of things are you referring to? What else is there to a lamprey? There isn't much left when you take out morphology. Eye color or personality?
And think I stated correctly "hasn't changed much" not "hasn't evolved".
Sincerely.
Only a few of an organisms genes specify its shape. Most of the genes control the detailed composition of proteins. There could have been wholesale changes at the cellular level, but you'd never know it from the fossil record.
That's not wild speculation, either. We observe such low-level divergence occurring in the real world, almost in realtime. Consider the wide variety of bacteria that exist in the world today, all sharing very similar morphologies. If you only knew the shapes, you'd never guess at the extreme variety.
The only really surprising result from this discovery is that an ecological niche has remained so stable for 360,000,000 years.