The vast majority of all living creatures are invertebrates. We do not yet even know the magnitude of their numbers, but research suggests that it is incredible. For example, in Panama, 100 new species of beetle have been discovered in a single tree! Aquarists with an interest in invertebrates have before them a lifetime of fascinating observations and discoveries. From the sessile corals to the intelligent, active cuttlefish, the surprises and opportunities are endless.