http://www.reefkeeping.com/issues/2002-05/rs/ This is just one link that will open the door for everyone to explore many more links and give you some words to google if you are interested in knowing more about these critters that could be in your tank. NO this is not an attempt to cause panic among members though it is something that many folks need to be aware of due to having some of these specimens pop up in reef aquariums. Isopods are commonly called Pill bugs, Rollie Pollies, and a whole slew of common names much like their Land dwelling relatives we all used to play with when we were children. There are several different types of differing body shapes, sizes, coloration as well as different "roles'' they have in our tanks. Some are just part of the clean up crew as algae eaters while others are parasitic on fish and shrimp, while some are just flat out predatory. In either case of parasitic or predatory Isopods can and will KILL fish. Parasitic usually latch on at night feeding on blood and drop off right after lights on while predatory once actively feed upon the fish until the food is gone being the fish. Parasitic Isopods feeding on the blood of the fish can cause inflammation in areas where they have fed and on smaller fish can lead to a quicker death while larger fish can tolerate this for longer unless the population is numerous. Plenty of information with pictures and descriptions of these crustaceans can be found easily. Note for the ones that are considered harmless to beneficial in our aquariums that eat algae primarily. They are the only KNOWN Isopod that can and will actually ''roll'' up like the land Pill bugs when they are handled. Most all of them are identifiable if enough time is taken to give the specimen a good look with a magnifying glass, doing things like counting segments and noting where certain legs are located or the shape of them. CAUTION -- Take care when handling one of these critters and do not allow one to sit on your skin without watching it closely as the ones that have spike like gripper forelegs use these to grasp prey or host while a second set of legs are like scalpels and SOME species can burrow into human flesh rather quick. As with anything that could be this or that without being certain about Identification you have two choices. 1) destroy the critter/ not putting it back into the tank to be safe. 2) Place the critter into a small cup with tank water or similar container and take many photographs then post them on Larc so others can help ID said critter while you do some leg work too. With option two you are giving the chance for you/others to learn something all the while you may just find out that you have an interesting Harmless/ beneficial critter in your ecosystem. After all if something is not ''bad'' for the tank or its inhabitants why not enjoy the diversity. If anyone finds a good link they would like to add in this thread to share with others please feel free. There are a ton of links out there, some great and some not so great. As always good luck and happy reefing BluewaterLa/ Mike.