Pellegrin rejected the validity of Monostichodus elongatus, described by Vaillant and type species of the genus Monostichodus, based on the lack of a proper species description, and redescribed Vaillant's specimens as Hemistichodus vaillanti. After review of the relevant articles in the International Code of Zoological Nomenclature, however, no arguments were found to consider M. elongatus as a nomen nudum. This implies that Hemistichodus should be considered as a junior synonym of the genus Monostichodus, which includes three valid species: M. elongatus (with Hemistichodus vaillanti as a junior synonym), M. mesmaekersi and M. lootensi.