The largest group of fanworm species with rigid chalky (calcareous) tubes belong to the Hydroides genus, and are easily recognised thanks to the shape of their beautifully ornate tube plugs. Hydroides is economically important as its members have the potential to cover immersed marine structures with massive nuisance settlements of chalky biofouling. The best-known example is Hydroides elegans, which settles on boat hulls so readily that colonies of it are perpetually in transit around the world, hitch-hiking to new places.