Final Answer:
The organisms referred to as salamanders that become sexually mature but retain morphological features of larvae, such as gills, are called "neotenic salamanders."
Step-by-step explanation:
Neoteny is a phenomenon in which an organism reaches sexual maturity while retaining juvenile or larval features. In the case of some salamanders, neoteny results in the retention of gills and other larval characteristics even after reaching reproductive maturity. This process allows them to reproduce without undergoing complete metamorphosis. Neotenic salamanders are able to reproduce in their aquatic larval form, providing an interesting adaptation that contrasts with the typical amphibian life cycle.
The retention of larval traits, including gills, can be advantageous in certain environments. Gills enable efficient oxygen exchange in aquatic environments, allowing neotenic salamanders to thrive in habitats such as ponds and other freshwater bodies.
This adaptation is particularly common in species of salamanders belonging to the family Ambystomatidae. The ability to reproduce without undergoing a full transition to a terrestrial adult form can be beneficial in habitats with variable conditions, where maintaining an aquatic lifestyle may offer a survival advantage.
In summary, the term "neotenic salamanders" describes those individuals that reach sexual maturity but maintain morphological features of larvae, such as gills. This adaptation represents a unique strategy among amphibians, allowing these salamanders to reproduce without completing the typical metamorphic process.