Tube Anemone (Cerianthus sp.)

Tube Anemones are a genuinely different animal from the clownfish-hosting anemones most reef keepers know, building a long, parchment-like tube in the sand that they retreat into instantly at the first sign of disturbance, extending a wide crown of fine, stinging tentacles when undisturbed. They're not reef compatible in the usual sense — those tentacles carry a potent sting capable of seriously harming fish and other invertebrates that brush against them, so they're best kept in a species-specific setup or well clear of anything you'd mind losing. A striking, almost otherworldly display animal for the right tank, not a community reef addition.