They look like tunicates to me. They have an incurrent and outcurrent syphon.
They are filter feeders and should not cause any problems in a tank. I've actually purchased larger species.
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72 gal bowfromt mixed reef sps dominated, 25 gal mineral mud type sump/refugium Skimmerless
2x250 14000k phoenix hqi 2x96 pc actinic, 50x flow
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