I wasn't a big fan of Moana. The characters just didn't connect with me. But I DID like Tamatoa! He reminded me of Deadpool, except as a massive crab-monster with a Kiwi accent in a kids movie.

Anyway, in his musical number there is a lyric that breaks through the 4th wall and demands you to investigate:

Maui man, you could try, try, try
But you can't expect a demi-god
To beat a decapod (look it up)

Look it up? OK... let's see... "decapod" eh?

....

This is a Coconut Crab

The coconut crab (Birgus latro) is a species of terrestrial hermit crab, also known as the robber crab or palm thief.

wiki

Let me use this one for some size comparison.

I guess the one on the left is an adult. The one on the right is a juvenile.

You couldn't pay me to touch one of these.

Anyway... aside from being the largest land-living arthropod (Phylum - Order: Decapoda) in the world, measuring in at an average of 1 meter (3ft, 3in) from leg to leg, there are many clues that Tomatoa is actually some kind of a glorified, anthropomorphized Coconut Crab.

1. Coconut Crabs are known to steal shiny things

Anything left unattended on the ground is a potential source of food which they will investigate and may carry away - thereby getting the alternative name of "Robber crab."

This is obviously the whole thrust of the song and the main property of the character, Tomatoa

2. Coconut Crabs are cannibals

Climbing is an immediate escape route (if too far from the burrow) to avoid predation (when young) by large sea birds, or cannibalism (at any age) by bigger, older crabs.

Exhibit A:

3. I heard about a thing where crustaceans can continue to grow so long as they have enough food and are unobstructed

I was looking this up but couldn't find anything quickly so I gave up. But one could assume that Tamatoa's grandma would have provided plenty of food to give him a good start!

Anyway, that's about all.

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