They are everywhere!
Admit it, the lampray is the perfect animal ~ untouched by the forces of Natural Selection ~ beyond mere statistics.
It appears by the most common classification schemes there are about 40 species of lamprey distributed among 9 or 10 genera and 3 subfamilies, lampreys themselves collectively constituting a family. This makes lampreys about as diverse as horses (that is including horses, zebras, donkeys, asses, etc). I wouldn't call that "pitifully few" species.
Yes, there are far more species of mosquitoes. But then, as you probably already know, insects in general are far, far, far more diverse in numbers of species than animals, and the distinction would be just about as striking in the case of any comparable analogy between animal and insect.
lampray is the perfect animal ~ untouched by the forces of Natural Selection ~ beyond mere statistics
I'm no expert on the critters, but at least at first blush I don't think I'd call all of the variation in living lamprey species "mere statistics". I think the differences in adaptation between living life-long in fresh water, versus a life cycle transitioning from fresh water to the ocean and back to fresh water, and even among the sea going lampreys some that are merely coastal versus others that appear to range across vast distances, and a range of (adult) feeding habits from pure parasite to pure predator, are at least a little bit "beyond mere statistics".