Among the early life histories of Cobitidae reported to date, external gills
always appear in the pre-larval stage except in the case of N.
Over the coming weeks an ancient life cycle will repeat: the larvae will hatch, grow, lose their external gills, develop legs and lungs, and move onto land as adults.
As it grows from infancy the hellbender only partially changes form, sprouting legs and losing its external gills but never quite outgrowing its youthful larval physique, and never leaving its watery environment.
There, they spend all their lives in a larval form, complete with external gills
and a tadpole-like tail.
V Observations on external gills
of juvenile of Ichthyophis bombayensis (Amphibia-Ichthyophiidae).
The biggest difference is that mudpuppies have very noticeable bushy, red external gills
, whereas hellbenders don't have external gills
Although the larvae lose their external gills
at about two years, hellbenders remain fully aquatic throughout their lives, never leaving the water.