First place on the planet definitely belongs to sperm whale. These mammals that can grow up to 18m are heavy 50t and produce incredibly loud sound of 230 dB, and the highest measured was 236 dB.

The second place belongs to much, much smaller animal, one of which you at least expect to produce sound twice stronger than Sharapova. It's a shrimp, and not just any, but a tiger pistol shrimp that grows only about 4-5 cm, and produces a sound of 200 decibels.

Bulldog bat is currently the loudest known bat in the world and it uses an extremely loud sound over 140 dB to track the movement of fish in the water (echolocation). Fortunately, people cannot hear this sound that could otherwise damage our hearing, since it is ultrasound and is happening at a frequency beyond human hearing.

Kakapo is a parrot species. It is unique in several ways: it is the only parrot in the world that cannot fly, it is the heaviest parrot, nocturnal bird, an herbivore and the male takes care of the cubs. It is also the loudest bird in the world!!

Crickets are somewhat less loud than bulldog bats, and their loudest measured sound is 120 dB and people can hear it at a distance of 2.4 km. Crickets use their sound to confuse birds, since all the crickets emit sounds that bounce off nearby objects, thus creating an echo that confuses predators so they cannot locate the pray.

Although the sound of roaring lions, in some way, became iconic, they are still far from the loudest creatures on Earth. Lions roar with strength up to 114 dB, and the sound can be heard at a distance of 8 km.

However, the loudest animal, in relation to its size is Micronecta Scholtzi, small aquatic insect size of 2 mm. They can produce a sound of 99.2dB. The most bizarre part of the story is that males Micronecta Scholtz insects produce this incredibly loud sound with their penis. Male "rubs" penis on the rough surface of the abdomen and thus creates this sound!