I've already discussed what I suspect is the reasoning behind Attina's design. To summarize, her crown resembles that of the Statue of Liberty, and the Colossus of Rhodes--the latter of which is Helos, the Greek God of the Sun, explaining her red and orange color scheme.
But what exactly is that spiky tiara made out of?
There are a few possibilities.
The spikes could be very smooth turritella shells. Or, the entire tiara might be cut from a single huge shell with exceptionally long spikes (a spider conch perhaps). The longer versions of her crown also resemble the spikes of a Crown of Thorns starfish.
Since Attina has more than one tiara, it could be "D, All of the above."
Harder to identify is the lifeform that she employs as a hat during the opening concert.
It seems to be some kind of ray. If so, it's either de-stingered, or Ariel isn't the only sister who likes to live dangerously.
There is of course, also the possibility that it's just a giant ocean mushroom, or something.