The Collaborative International Dictionary
Perennibranchiate \Per*en`ni*bran"chi*ate\, a. [See Perennial, and Branchiate.]
(Anat.) Having branch[ae], or gills, through life; -- said especially of certain Amphibia, like the menobranchus. Opposed to caducibranchiate.
(Zo["o]l.) Belonging to the Perennibranchiata.
Wiktionary
a. (label en obsolete of some amphibia) having gills throughout life
Wikipedia
Perennibranchiate, in zoology, is the condition of an organism retaining branchae, or gills, through life; This condition is generally said of certain amphibia, such as the mudpuppy; the term is opposed to caducibranchiate. In some cases only a small proportion of a given amphibian population is perennibranchiate, but in other instances a preponderance of the individuals have an adult gill retention. For example, in the case of the Rough-skinned Newt in the Cascade Mountains populations, approximately ninety percent of the adult population is perennibranchiate.