[5] The body color ranges from dark brown to yellow orange and this species has two or three white bars.

[4] In some varieties, typically those specimens initially associated with Heteractis crispa anemone, the saddle shape may extend up onto the fish's Dorsal fin with a third white bar or margin located across the caudal peduncle,[4] (pictured in taxobox).

[13] A. polymnus has a diurnal activity, is aggressively territorial and is dependent on its host sea anemone which it uses as a shelter for the group and for the nest.

[6] Both species of sea anemone, which host A. polymnus, are known to bury themselves in the sand when they are under stress, leaving the fish vulnerable to predation.

It has been suggested that the almost equal size of the male is an adaptation to allow it to elude predators by erratic swimming in the water column or covering the relatively long distance to shelter in coral rubble.

Like corals, anemones contain intracellular endosymbionts, zooxanthellae, and can suffer from bleaching due to triggers such as increased water temperature or acidification.

This is due to the poor survival rate of wild collected specimens and the overall shortened lifespans these normally centarian[citation needed] organisms often experience in captivity.