Long spine urchin question

[TiggrReefer]

As you view the video, what is happening with the movement of the “blue dots” in the center?
What sources do you consult if you want more detailed information?
Thanks

 

[ISpeakForTheSeas]

I would guess (quite possibly incorrectly) that those are the tube feet blowing in the flow of the tank.

I'll give you a bump for others to hopefully list some sources for you.