One of the most common and inexpensive creatures, it can assume a variety of shapes as it expands and contracts as it pumps water in and out of its body. Many of the poses are quite graceful and beautiful. This is the first specimen I obtained (for free, with some live rock), and I was fascinated with it for weeks.
The first time I woke up and saw my anemone looking like this, I panicked and called the aquarium store. Anemones often expel all of the water inside their bodies, to excrete wastes, and I had no need to be concerned.
Waving its tentacles with wild abandon.
The view from on top: it looks a lot like a flower. The bulge in the middle is in fact a mouth.
Very tiny indeed, with clearly visible excretion.
A close-up of the mouth, eating a piece of macro algae which wandered by.
Yet another strange shape, with the bulk of the body as a bulb, and the tentacles mostly deflated.
Another pose with the "foot" very tall indeed, and the tentacles searching widely for food.
A slightly different atlantic anemone, called a curlicue anemone. The tentacles have a very fine, crinkly shape.