What are the rest of seven underwater kingdoms?

Copy-pasting my answer to What are the Seven Kingdoms in Aquaman? on SFF:

1. Atlantis. No need to explain that one, I think.
2. Xebel, ruled by King Nereus. IIRC Xebel isn't shown in the movie.
3. The Trench, inhabited by monsters.
4. The Fishermen Kingdom, land waters of the mermaid-looking people.
5. The Brine, with its crab-like people, and where the final battle begins.
6. The Deserters Kingdom, now buried in the Sahara after it was draught.

7. The Hidden Sea (in Earth's Core, no less), where Atlan's trident was hidden, and which can be accessed from the portal thingy beyond the Trench.

While there is quite a bit we do not know about the fictional fantasy world of Atlantis, we have been told that Atlantis split into 7 kingdoms. Four specifically mentioned in the movie, three to remain largely a mystery, or at least a puzzle, but truly six kingdoms are represented in the movie.. Fandom's website has listed all seven, but their pages are little more than placeholders for future content. It stands to reason:

1. Atlantis, remains a kingdom

The seven kingdoms split from Atlantis, but did not destroy Atlantis. Atlantis, and three other kingdoms allegiance were necessary for King Orm to hold the title Ocean Master.

2. The Fisherman Kingdom

...seem to go along, reluctantly. As Arthur/Aquaman and Mera head off to find King Atlan and the Trident, they fight off creatures from the

3. Trench Kingdom,

diving into the water to find the

4. Missing Kingdom (aka the Lost Nation)

where King Atlan leaves cryptic clues to the location of his famed Trident. Their journey continues when they, quite unexpectedly, find Mom/Atlana in the center of and at the bottom of the ocean in what appears to be a rather nice piece of real estate. Stuck for a couple of decades because she wasn't able to get the Trident herself (the key to leaving). This idyllic setting is likely the:

5. Deserter Kingdom.

Apparently, the only people able to speak to sea creatures are King Atlan and Arthur/Aquaman. Once the gi-normous crustacean stops fighting Arthur/Aquaman, it breaks free from the lava laden depths to help Aquaman claim his title as True King/Ocean Master. The scene takes place in the

6. Brine Kingdom

The only kingdom that I do not remember from the movie is

7. Xebel

Once ruled by Mera and originally an "other-demensional" kingdom, now a penal colony for Atlantean crimes. But don't confuse that with the name Xebel, there seems to be some confusion between film and comic references. In the comic, King Nereus is Mera's fiancee, not father.

Aquaman's Seven Kingdom of Atlantis, Explained: But it's possible -- maybe even likely -- that the Lost Kingdom is actually where Arthur and Mera discover Atlan's tomb, the Hidden Sea at the Earth's core.