|MadSci Network: Zoology|
The giant green anemone (Its scientific name is Anthopleura xanthogrammica, if you're interested) is common along the Pacific coast of North America, from Alaska all the way to Panama. So, if you looked in the right place (tide pools and deep channels, on rocky shores) in Oregon, you'd probably be able to find some. The giant green anemone can grow to be larger than a foot in diameter, and can live for several decades. I've attached a couple of pictures I found.
When I looked around, I found that these anemones like to eat lots of things, including crabs, sea urchins, and small fish- basically whatever they can catch. But most of all these guys like to eat mussels: they're usually found around mussel beds, and they eat mussels that get dislodged from the beds and swept to them by water currents. Anemones, which are very similar to corals, are a class of animals (called Anthozoans) in the phylum Cnidaria, which also includes Jellyfish. Cnidarians share with jellyfish something called nematocysts, or "stinging cells". Anemones have stinging cells on structures called acontia, which look like little white threads on their tentacles. When they capture prey they wrap their tentacles and acontia around it. The nematocysts discharge, releasing a toxin into the prey. Once the prey is sufficiently subdued, they can take it into their mouth at their leisure. The giant green anemone also has little symbiotic algae cells that live inside cells of the digestive layer. In exchange for a place to live, and a little carbon dioxide, these algae release small amounts of sugars into their host anemone.
Because these anemones can get so big, and live so long, I don't think there's a lot of predation on them. I have been able to find references to them being fed on by sculpins (a type of small fish), sea snails, and sea spiders- I've attached a picture of each.
Try the links in the MadSci Library for more information on Zoology.