Correct, which is why they are used so much in scientific research. One of mine had lost the tip of one of his gills, which has now grown back, but is branched.
They are critically endangered and possibly extinct in the wild (basically 1 area of lake in Mexico city), but will never be completely extinct due to breeding for scientific research and the pet trade.
They also have both external gills and internal lungs.
They are neotenic - they reach sexual maturity whilst still in the juvenile form.
Their eyesight is not good, they are goofy, look like a cartoon character and are far from graceful.
They are adorable, cute, amazing, and are pretty much guaranteed to raise a smile or chuckle with their antics.