The animal which can live both on land as well as in water are called:
a. Polar
b. Hydro-lithozoan
c. Reptile
d. Amphibian

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These vertebrates use their skin as a secondary respiratory surface and lack lungs and rely entirely on their skin for some small terrestrial animals.

Complete answer:
Option A is incorrect. The north polar region's animals may be seasonal tourists on the horizon, permanent High Arctic inhabitants, or anywhere in between. Such as polar bear, it has developed into a narrower ecological niche, with many body characteristics adapted to cold environments, to travel around snow, ice, and open water, and to hunt seals that make up much of its diet. While most polar bears are born on land, much of their time is spent on the sea ice.

Option B is incorrect. Hydrozoans or Hydro-lithozoans are a taxonomic class of very small invasive human creatures, some solitary and some territorial, the majority of which live in saltwater. They live in colonies that may be huge, and in some cases, the individual specialized animals may not survive outside the colony. Within this class, several genera live in freshwater. Hydrozoans are similar to jellyfish and corals and belong to the Cnidaria phylum.

Option C is incorrect. The class tetrapod animals of Reptilia which include tortoises, crocodilians, snakes, amphisbaenians, lizards, tuatara, and extinct relatives. They are vertebrate tetrapod creatures that either have four limbs or descend from four-limbed ancestors, including snakes. Reptiles do not have an aquatic larval stage, as opposed to amphibians. Most reptiles are oviparous while some groups of squamates, including several extinct aquatic clades, are viviparous.

Option D is correct. Amphibians are class Amphibian ectothermic, tetrapod vertebrates. To the Lissamphibia, the group belongs to all living amphibians. They occupy a wide range of environments, with most species living within aquatic ecosystems that are marine, fossorial, arboreal, or freshwater. They typically start as waterborne larvae, but some species have developed behavioral adaptations to overcome this. Their metabolic rate is poor and as a result, their needs for food and energy are minimal.

So, the correct answer is Option D.

Note: Amphibians are also ecological indicators with their diverse reproductive needs and permeable skins; in recent decades several species across the globe have seen a drastic decrease in amphibian populations.