A reader asked where one might be able to purchase small, tropical aquatic worms. Presumably this would exclude the giant tube worm, which lives near undersea volcanic vents and can grow to over seven feet in length. However, for the buyer interested in purchasing tropical aquatic worms of the smaller variety, a number of options abound, including flatworms (phylum Platyhelminthes), roundworms (Nematoda), segmented or “fan” worms (Annelida), and arrow worms (Chaetognatha).