Anyone knows what's this?

[EeyoreIsMySpiritAnimal]

Put the chaeto back in the bag, and take it back to the LFS for a refund.

Unless you got it for free... Then I could see rinsing it well and inspecting for other pests, and then using it. But I wouldn't pay $$ for chaeto with Aiptasia in it

 

[DeadEnd]

Unless you got it for free... Then I could see rinsing it well and inspecting for other pests, and then using it. But I wouldn't pay $$ for chaeto with Aiptasia in it

It wasn't free... I paid $20 for it... The provider is one of their employees so they were confident to say it was "clean"...