Pest ID please

[oryansreef]

I was moving a frag and found these on the bottom of the plug. I thought they were flat worms and treated with some funky brand of flat worm treatment and did nothing. People I've seen using flat worm exit seems to make corals mucus and this stuff did not.
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[xilez]

Nudibranches? Flatworms are red I think

 

[oryansreef]

xilez;1099389 wrote: Nudibranches? Flatworms are red I think

Good, bad? I see them on an acan frag they go in between the frag and plug. Also clam doesn't look good

 

[bhodges82]

They look like stomatella snails to me.

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[bhodges82]

Or ostracod

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[jennm]

Nice clear picture but I can't quite tell either. Can you tell if they have hard shells or not? I don't think they are necessarily a pest.

Jenn