April fool! This ‘snail shell’ isn’t quite what it seems…

When is a snail not a snail? What if it’s something totally, completely different? This mollusc-like shell was described as a new species of¬†trochid in 1903, but in fact it comes from an entire different¬†phylum (one of the highest levels of distinction between animals). Any ideas what it might be instead? … It’s an anemone!…