The genera Reclinomonas and Histiona are very closely related on the basis of ultrastructural characters. In the former genus, with the one species R. americana, there is no prominent ventral sail, the lorica is laterally flattened, and the lorica bears scales. In the latter genus, with the species H. velifera and H. aroides, there is a prominent ventral sail, the lorica is not laterally flattened, and scales are absent. The species H. campanula, known only from one report, has a prominent ventral sail but also a laterally flattened lorica; there is no information on lorica scales. It is unclear whether this species should be referred to Histiona or Reclinomonas. As more species are discovered, it may prove that there is no valid reason to recognize two genera. If so, species of Reclinomonas would be placed in Histiona, because Histiona is the older of the two genus names and therefore has priority.
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