External gills, functional eyes, tailfin--the larval grotto salamander has all three.
Currently there are 191 named species of salamanders in the USA. This large amphibian grouping is contained in 8 families of which the largest by far is the Plethodontidae with 147 species plus well over a dozen subspecies. With the use of genetics it is probable that an additional 25+ species will soon be added to this family.

The plethodontids vary in size from 2” long dwarfs to what are considered in this family comparative giants of 9”. Among these are species that are entirely aquatic throughout their lives (paedomorphic taxa), others which are just as entirely terrestrial, and many that are in between these two extremes. Most seek seclusion beneath logs and rocks in damp woodlands, some prefer a similar microhabitat along stream edges, and others live beneath rocks and leaf litter submerged in streams, creeks, or rivulets. Terrestrial taxa have well developed, fully functional eyes, some aquatic forms have reduced vision, and some aquatics are blind. And then there’s the grotto salamander, Eurycea (formerly Typhlotriton) spelaea, a most remarkable little beast that may be encountered in the cave systems of Southeastern Kansas , Northeastern Oklahoma, Southern Missouri and Northern Arkansas.

Troglodytic when adult and in its later stages as a larva, after hatching the larvae often follow connecting underground streams from the darkness of caves to the daylight outside. At that point they are pigmented, being a weakly patterned olive brown to tan. They then have functional eyes, 3 pairs of external gills, and a well-developed tailfin. During the daylight hours they, like many aquatic salamanders, hide beneath rocks and stream bottom debris. On cloudy days and at night they are more inclined to depart their lairs, swimming and foraging in the open.

After a larval duration of several years the 3 or 4 inch long larvae follow their home streams back into the darkness and undergo a metamorphosis that is typical in some respects but atypical in others. Simplified, typically the gills and tailfin lessen in size and function until they are fully resorbed and the larvae become capable of existing terrestrially. Atypically the pigment of the now subterranean salamander is gradually lost and rather than becoming lidded and terrestrially functional as do the eyes of other plethodontids, the eyes of the grotto salamander degenerate and the lids fuse, producing at adulthood a pinkish, sightless, terrestrial, troglodyte.

Welcome to the wonderfully complex world of Mother Nature.