A, the main characteristics of reptiles: the body surface is covered with horny scales or nails, breathing with the lungs, the body temperature is not constant, it will change with the change of external temperature. The heart has only three cavities, and there is an incomplete diaphragm in the ventricle, which is fertilized in vivo, and the eggs are ovoid or a few viviparous. Because the eggs laid are chorionic eggs with hard shells, the reproductive development of reptiles is completely out of the limit of water, such as turtles and crocodiles. A is wrong.

B, giant salamander and salamander belong to amphibians, and B is correct.

Hippopotamus is the largest omnivorous mammal in freshwater species, and its body is huge.

Most crustaceans are aquatic, and there are many marine species. The body is divided into head, chest and abdomen, and the head and chest are covered with hard head breastplate. Almost every limb has 65,438+0 pairs of appendages, and often maintains the original double-branched shape, with 2 pairs of antennae, breathing through gills. D error.

So choose: B.