well they DO look like the creature from the black lagoon, just wiki it.

Obviously mirelurks are there to fufill the "Its-a-guy-in-a-suit" aesthetic of some of the monsters.

Regarding the specific vault, no they're not from there. If you go into the flooded basemant, you can find one of the tapes that chronicles the fact that the Vault had a consistent problem with water leaking and the like--eventually the pipes burst it seems, flooded parts of the vault and allowed some of the walls to cave in. The crabs moved in shortly thereafter.

At least that was my understanding of the situation.

I think it's because Crabs and Turtles are Neutral towards eachother. Maybe under the Turtle's "Rule", they live with eachother for a form of protection or one of the two gets food.

Or mirelurk king is just a name and they have no actual authority.

No....not really.

The Creature from the Black Lagoon really looks like a Zora or something....or just your stereotypical fish man. The Mirelurks, well they're crab people. There's a huge difference between the Mirelurks and the creature, and that difference is: Mirelurks are crabs with bodies, the Creature is a man with fins on his head.

If you ask me, the think that looks the most like Mirelurks are Crab People from South Park, even though the Crab people are more lobster-like than crab-like.

<.<;

The mirelurk KINGS resemble the creature from the black lagoon.

The normal mirelurks look like a guy in a kaiju suit on the next godzilla film.

"Oh no, it is crabbor! We must run!"