Its larva drifts in open water for months and was, for a long time, classified as a completely different animal.
Tube anemones have a planktonic stage so unlike the adult, and so long-lived, that early naturalists described these larvae as their own genera with their own names. They are transparent, tentacled, and they swim in the open ocean for weeks or months while the adults spend decades in a single hole in the sand, which is roughly the opposite of what most sedentary animals do with their larvae. Some of them even reproduce while still in the larval form.
The adult is a night animal. By day the tube in the sediment holds nothing visible; after dark the crown comes up, a ring of long banded tentacles with a second short ring around the mouth, and it fishes for plankton drifting past. Touch the sand anywhere near it and the whole thing is gone before you register the movement, drawn into the tube by a muscle that runs its length.
It looks like an anemone and is not one, and it lives where anemones cannot: soft sediment, with no rock to attach to, held in place by a tube it built itself.
- two sets of tentacles: a long outer ring and a short inner ring around the mouth
- banded tentacles, brown and cream
- rises from a soft tube buried in sand, and vanishes into it instantly
- out at night, closed by day
