Are there any telltale features used to ID the Atlantic Carpet, Stichodactyla helianthus? I'd really hate to pick one of these up since they aren't even a host anemone for clowns.
The difference is more subtle - they can sometimes be mistaken for mertensii.
First, they are brownish in color. I have never seen a colored one (though sometimes the tentacle tips can have spots of color). If you see a colored carpet it is almost certainly NOT a helianthus.
Second, helianthus, though brown/tan, will often have two different colored tentacles (lighter/darker) so that the surface of the anemone looks somewhat checked.
Third, the tentacles of helianthus are fat and stubby. They are considerable fatter than any of the other carpets. Other carpets can often display stubby tentacles (particularly haddonis, but sometimes gigantea and mertensii when stressed), but they are much smaller and look like bulbs packed tightly together.
Fourth, helianthus has dark verricuae that are visible on both upper and lower parts of the column, but they are considerably less numerous than that seen in mertensii. Additionally, the helianthus verrucae are typically brownish colored, while mertensii verrucae are often vibrantly colored.
Sorry about these photos - they're all I have handy
