The African elephant is the largest animal species on land, with the largest individuals growing up to 4m tall, but it is dwarfed by the largest marine animal, the blue whale, which reaches 30m in length. The vast size of the blue whale is an example of how large animals can grow when unconstrained by the effects of gravity. The buoyancy provided by the ocean means that sea creatures can grow as large as is necessary to support their existence, and such whales need to grow large enough to prevent them from losing too much body heat to the surrounding water. They are, like elephants, warm-blooded mammals after all. However, the blue whale is not the only marine animal to grow to vast sizes – there are many deep-sea creatures that similarly dwarf their terrestrial or shallow-water counterparts, a concept known as deep-sea gigantism.

The giant isopod (a massive crustacean related to woodlice, shrimp, crabs, and so on) is just one example of a deep-sea dweller that grows much larger than its terrestrial relatives. Living on the ocean floor at depths of over 500m, its body length can grow up to 50cm, which is impressive considering that terrestrial and shallow-water isopods rarely exceed 3–5cm in length. Similarly, the Japanese spider crab occupies the same habitat, and its carapace, the main part of its body, can reach 40cm, while its claws span up to 3.7m. In comparison, the European spider crab, a related shallow-water species, only reaches a carapace length of up to 20cm and claw span of 50cm.