Today I noticed a different form in the substrate, one I'd never seen before. The tank is 4 years old, so that was quite a surprise. I must have imported himwith the rocks and creatures I added on 9/Oct . I recalled seeing something similar in shape in "What Invertebrates?: A Buyer's Guide for Marine Aquariums", which is a simple book but good enough for basic aquarists like me. The thing that looks like the picture is a Chiton, which the book says is safe. Looks like ...