Aiptasia
1-(EXCERT FROM BAENSCH MARINE ATLAS VOLUME 1) follows;
Rock Anemones - There are pronounced pests among the anthozoans. The rock anemones of the genus Aiptasia can - once introdued with live rock - multiply rapidly in a reef tank. Their potent toxin injures other anthozoans. Large rock anemones can also be a threat to smaller fishes. Mechanical control of these animals is practically impossible. If they are smashed, countless new polyps develop. Only chemical and biological controls remain as options. You can kill aiptasids by injecting a small quantity of hydrochloric acid into the body of the polyp using a hypodermic needle. A few drops are sufficient. These small quantities do not affect the buffering capacity of the aquarium water. The disposable syringe and the 30% hydrochloric acid can be purchased in a drug store. However, when trying to control heavy infestations, this method turns quite laborious and cumbersome. Using fishes to biologically control them would be easier. There are a few butterflyfishes which devour rock anemones with a pleasure (e.g., Chelmon rostratus, Chaetodon kleinii and Ch. lunula). In one or two weeks one Chaetodon can totally free even a heavily infested aquarium. Unfortunately, there is a reason why this idea was intorduced conditionally. The import of these fishes is forbidden in some countries. This method to control aiptasids is only available to our foriegn friends. The only alternative open to hobbyists that cannot import the fish is Chemical control. Feed artemia and Brachionus sparingly as soon as rock anemones begin to multiply heavily. By the way, rock anemones multiply significantly faster in poor water (high nitrate and phosphate concentrations) versus clean water. Good water quality is a control measure against unwanted parasites.
2-(EXCERTS FROM THE REEF AQUARIUM BY DELBEEK/SPRUNG) follows;
Preditor of aiptasia juviniles/ not sure about larger animals - Dancing or Peppermint shrimp (Rhynchocinetidae). Although they can be utilized to eat juvenile aiptasia animones they will not restrict their diets to just this one food item and will eventually attack other cndarians. Note: though they have similar appearance and the same common name, do not confuse this species with lysmata wurdemanni, a cleaning shrimp which does not feed on cnidarians.
Small anemones belonging to the genus Aiptasia can be a real problem in some reef aquariums. If these small anemones are allowed to grow on tridacnid clams, they can reach underneath the mantle and sting the clam. This will result in the mantle pulling away and the clam will eventually die.
HOPE THIS HELPS SOME WHAT. YOU MAY WANT TO GET A SECOND OPINION ON JUST WHAT THE ANIMAL IS AS THE PICTURE IS NOT QUITE FOCUSED. ANYWAY THIS IS MY TWO CENTS. THERE ARE LIQUIDS ON THE MARKET FOR DEALING WITH THIS ANEMONE. CHECK OUT MARINE DEPOT, DRS FOSTER AND SMITH, OR ANY OTHER LARGE OUT LET YOU WILL FIND SOMETHING THERE. OR JUST MIX UP A SMALL STRONG MIXTURE OF KALK AND INJECT THAT. GOOD LUCK.