It has a characteristic inflated air pocket. This animal feeds on various nematocysts, and the effects of it's touch varies depending on the nematocyst it consumed. If tentacles of nematocysts are still stuck to the skin, they need to be removed gently. Be careful not to squeeze them as to not discharge more nematocysts. Local anesthetic spray or ointment may remove some of the pain on minor stings.
Tannic acid is believed to work well.
Give cardiovascular and respiratory assistance if needed. Benadryl cream isn't as effective. Commercial creams don't work as long. Severe itching may occur after a few days.