Sand sifting star breeding?

[Littlemikey]

I have had two sand sifting stars in my tank for several months and for the past three days one has been on top of another hitching a free ride. I’m curious if this is breeding habits or what. The one on bottom is clearly alive and well as it’s moving around. From what I have read this Specias does not mate in this manner

 

[cristata.reef]

Sand sifters (Archaster typicus) <-- most/all places list it as Astropecten polyacanthus but they're wrong, are broadcast spawners meaning that they release gametes into the water column. They have never been successfully bred in captivity

 

[Littlemikey]

Figured as much thanks

 

[Sallstrom]

I have had two sand sifting stars in my tank for several months and for the past three days one has been on top of another hitching a free ride. I’m curious if this is breeding habits or what. The one on bottom is clearly alive and well as it’s moving around. From what I have read this Specias does not mate in this manner

This is a common thing to see them do in aquariums. They are preparing to spawn, synchronising so they are ready to realise their gametes at the same time. The male are on top. Read more here:
https://en.m.wikipedia.org/wiki/Archaster_typicus

/ David