The presence/absence and number of vaginae is essential for the systematics of the Monogenea. Two genera share similar morphology and anatomy but are distinguished by this character: Pseudaxine Parona & Perugia, 1890 has no vagina, Pseudaxinoides Lebedev, 1968 has multiple vaginae. During a study of Pseudaxine trachuri Parona & Perugia 1890, we found specimens with structures resembling multiple vaginae; compared them with specimens without vaginae in terms of both morphology and molecular, and found that they belonged to the same species. We investigated its male copulatory organ and found that it is armed with a single circle of 12 hooks and a central stylet which is probably involved in traumatic insemination. We redescribed Pseudaxine trachuri based on newly collected specimens from off Algeria and Museum specimens from off France. Specimens from the type-host, Trachurus trachurus, were found to be similar, for molecular sequences and morphology to those found on Boops boops. We confirm that B. boops is a host of this parasite. We consider that Pseudaxinoides was erected on the basis of an erroneous interpretation of structures which are not vaginae and propose the transfer of most of its species to Pseudaxine.