Monumentials

Monumentials are giant sea creatures, thousands of years old and many times bigger than the Aronnax. According to Nereus, the name Monumential is the Lemurian term for 'Mega Big'.

They are distributed in all the oceans around the world. Of the 8 Monumentials shown on Queen Doreus' Sceptre, 6 are known as of Season 3: the Terror (Kraken), the Sea-Worm, Tartaruga, the Electric Ray, the Jellyfish, and the Pistol Shrimp.

The Monumentials can be controlled by the Sceptre of Queen Doreus that is hidden in Lemuria and was crafted 6,000 years ago by Zeberus.

Proteus and Alpheus wanted to control the Monumentials to bring chaos to the world.

History
6,000 years ago, Queen Doreus of Lemuria used her scepter to send the monumentials into a deep hibernation. They have only recently started to awaken.

Sea Worm
A gigantic Sea Worm that was assumed to be a long undersea tunnel. It rests behind an underwater current resembling a waterfall. It feeds by inhaling micro-organisms from the current.

According to Nereus, it's one of the smaller Monumentials. It is the first the Nekton Family discovered, and one of two that were found in Season 1.

Tartaruga
A gigantic Sea Turtle that was assumed to be an island for many years. It rested on the surface of the ocean and a small village was built on top of its shell prior to its awakening.

The Tartaruga is also part of a certain island's legend; basically, if the islands water become filled with jellyfish, the Tartaruga will be summoned to devour them.

Electric Ray
A gigantic Electric Ray that used to sleep off the eastern coast of Central America. Its ability to attract and generate electricity is so great, it creates a never ending electric storm that follows it wherever it goes. This storm is called the Catatumbo Storm after the bay in which it originated.

In Season 3, the Ray wakes up and tries to free the Kraken (for unknown reasons) by using his electricity to try to open the gate behind which the Kraken is trapped. However, Ant succeeds in using Queen Doreus' sceptre to put the Ray back into deep sleep.

Kraken
A gigantic Squid, and the most fearsome of all the Monumentals. It rested just behind the gate to the ruins of the hidden city of Lemuria. According to Nereus, the Kraken was responsible for the destruction of Lemuria 6,000 years ago.

Pistol Shrimp
A gigantic Pistol Shrimp that is able to snap its huge claw with enough speed and force to create a powerful shockwave.

6,000 years ago the enemies of Queen Doreus tried to wake the Pistol Shrimp to use against Lemuria. The plan backfired as the Monumential destroyed the ship, resulting in the death of the entire crew.

It made its debut in the series in Season 3. The Nektons (and the Dark Orca Pirates did, in fact, survive the first snap, but it dealt major damage

Jellyfish
A gigantic jellyfish, large enough to entrap two massive submarines inside it and still give both ample room to move around. Its tentacles are highly corrosive, as is the inside of its bulb.

It is first seen when the Nektons find its tentacles, not knowing what they are. It makes an appearance in Season 3 and is the sixth Monumental the Nektons have encountered.

Alpheus tried to wake the the jellyfish, but when he found the Monumential, the jellyfish had long been awake, although the exact reasons for this are unknown. Alpheus was then trapped in the jellyfish for three months while his submarine was slowly digested before he was finally rescued by the Nektons.

The encounter with the jellyfish had far-reaching effects on Alpheus, as after his rescue he finally gave up his plans to use the Monumentials to conquer the world.