OK, so here's my AMAZING mini-brittle star story:
I have hundreds of these little buggers all over my live rock of my nitrate high reef system. Yesterday, upon doing a water change (including a 6-month storm major disturbance in the tank) I was aghast to see the following thereafter:
They all started spawning in mass, in the following bizarre fashion: I notice they had all emerged from hiding in rocks, slithered to a local high point in the wide open, did a hand stand with booty shake for about 5 seconds and then looking like they were excreting a fine brownish waste during this strange handstand. But then I suspected they were mass spawning. During each typical spawning, once the handstand discharge dissipated, each returned to normal slithering, and apparently calmed down and eventually returned to the rock. I promise I am not joking nor exaggerating; I sat their with my mouth ajar for about 10 minutes. I also notice some of them apparently moving a little wad (or package) of something from the base of their body, moving in with the cillia of the arm, until the the wad reached the end of the arm, upon which is was let go.
This is one of the strangest things I have ever experienced in my system. Has anybody else seem such?
The source water for the water change was natural sea water from my local aquarium, which I treated to increase salinity, alkalinity, iodine, and M/S. This may be part of the puzzle.