Canon Elan IIe, tripod
|One of my favorites|
In establishing and decorating my ecosystem, I gathered a few 'living rocks' from the river, stones with plant life and barnacles on them. One small stone the size of my palm turned out to be populated far better than I thought.
I had spotted the numerous barnacles, but what I didn't see in my flashlight beam was the colony of anemones all over the surface. Anemones contract themselves into a tight ball when danger threatens, so once I'd handled the rock they had made themselves practically indistinguishable from the stone itself. But after only a few minutes in my tank, they had 'blossomed' out into feeding mode, extending the stalk of their body and a bloom of small arms at the head.
To the best of my knowledge these are commonly known as "triffids" or "glass anemones," more scientifically known as the genus Aiptasia. In researching this, I learned that those who maintain reef aquariums generally try to get rid of them because they reproduce quickly and may eat fish species that the owner wants to keep. From my perspective however, they were permitted to make as good a go at it as they could, and I liked their appearance. Not very many things in the tank were vulnerable to them anyway.
This is the largest example, and appears to be a different species from some of the others - others don't have the triangular mouth opening in the center, but rather a flat one. The full spread of arms around the head measures roughly 1.5 cm across. You're looking directly at the top of the anemone and straight into its mouth, which feeds directly into the stalk of the body. You can also see a sequence of this one feeding at this link.