Good or Bad anemone?
 

I have recently purchased some live rock. On it has appeared an anemone that is brown with whitish stripes, fairly long tentacles and is the size of a quarter.

sounds like aiptasia.

Aptasia?

Aptasia?
 

Next question is what to do with it?

Sounds like a manjo. Put a shell over it and it will transfer to it, then through it out.

Finally a Pic
 

here it is hope this helps

How big is it?

Majano's more likely my guess.

Ken

Size
 

It is the size of a nickle to quarter

aptsia
 

if its brown and not green it's aptasia-if you only have one you can inject it with lemon juce,or mix up a thick paste(about the thickness of chowder) of kalkwasser and cover it including the base

could be either from the pic Majano's have a bulbous tentacles aptasia is also called the glass anemone and have long slender tentacles both are very common on LR. Majano anemone are a bit harder to get ride of as far as using chemicals to do the job. Because not all that work on Aptasia anemone will work on Majano anemone, joeys juice works well on both as it melts them but peppermint shrimp work the best and some wrasses have been reported to eat them also.

Bill