Last night, I attempted to make a large Hallucigenia sculpture, but I couldn't get the spike-like legs to stay on so I destroyed it. I tried again with a smaller, simpler piece. The key was to attach the legs before the tentacle-like structures on the back. Of course, this is all based on an obsolete interpretation of the fossil. Hallucigenia really walked on the tentacle-like structures and had the spikes protruding from its back.
