Alpine newts (especially 2 the Italian subspecies) are very prone to retaining their gills and some larval characteristics for a couple of years, but not as many become truely Neotenic (adult retaining larval characteristics) though it does happen more than in many other species. Triturus species quite often retain gills for a couple of years, but again, not many will become truely Neotenic. For example, as far as I know, there is only one documented case of true neoteny in Triturus marmoratus, and none for T. pygmaeus. Lissotriton species are quite prone to neoteny, there are lots of cases of Neotenic smooth newts, Lissotriton vulgaris. A lot of cases of neoteny end up just being 'arrested development' and many newts which retain larval characteristics for 2-3 years do eventually look just like normal adults of the species, however they are still fascinating.