Mating sand sifting stars?

[PsychFish13]

i have 2 sand sfiting stars and they seem to always on top of each other. I noticed this behavior at the LFS but no other idea other than mating or eating that they'd do this. The one on top is not distending its stomata or appear to be hurting the other star. The top star is always the darker, smaller creature. Am I missing something?

[dan]

mine are allways doing this. been doing that for five months now. i think they just like that.

[::pete::]

There was just a thread on RC for the same thing. They are mating.