larvae fed sewage worms (Tubifex)--a heterospecific prey—under the high-density conditions, head width increased, but body size remained unchanged. Development into the cannibalistic morph is thus influenced by both chemical and visual cues of density and diet. Observations of wild populations revealed that cannibalistic dimorphism within ponds was limited to early periods of development and disappeared as development progressed. Reproduction and Life Cycle The breeding season of the Ezo salamander runs from April to May, with eggs hatching between early- and mid-May. The species has a biphasic life cycle, with the first stage of life spent as aquatic larvae and the second, after metamorphosis, spent on land as a terrestrial adult. Development Ezo salamanders develop interdigital membranes on their fore- and hindlimbs during their juvenile stages. The forelimbs develop first, as is the same of other salamander species that spawn aquatic larvae. The earliest stages of forelimb development showcase morphology similar to a spear, with symmetrical digits developing on either side of the pointed interdigital membrane until the limb adopts three digits and the membrane disappears. This trait is commonly seen in other aquatic larvae that live within ponds but is absent in larvae that develop in quickly flowing streams. Paedomorphosis The population of H. retardatus found within Lake Kuttara exhibited paedomorphosis, a mechanism where adults maintain larval features even after metamorphosing and reaching sexual maturity. While this mechanism is common in many salamander species—found in nine of the ten salamander families—it is rare in the Hynobiidae family, recorded only in H. retardatus and the Longdong stream salamander (Batrachuperus londongensis). Paedomorphosis of the Ezo salamander was first recorded in 1924 within the Lake Kuttara population and was last encountered in 1932. These H. retardatus individuals were sexually mature but morphologically similar to the larvae of the species, with features such as external gills and caudal fins. The exact year of extinction for this population is unknown but can likely be attributed to the introduction of salmon into the lake habitat. After the loss of the Lake Kuttara population, paedomorphy in H. retardatus was not documented for almost 100 years and the trait was presumed to have gone extinct. However, on December 1, 2020, and April 5, 2021, three male paedomorph-like individuals were documented in the Iburi subprefecture within 40 km of Lake Kuttara. The three individuals were 14% smaller than metamorphosed males when comparing snout-vent lengths and 2.26 times larger than