We herein redescribe Allobenedenia dischizosepta (Suriano, 1975) n. comb. (Monogenoidea: Capsalidae) based on light microscopic analysis of the holotype and 18 paratypes from the gill of Acanthistius brasilianus (Cuvier, 1828) (Perciformes: Serranidae) along with light and scanning electron microscopy of 25 newly collected specimens from the gill of Acanthistius patachonicus (Jenyns, 1842) (new host record) in the southwestern Atlantic Ocean off Argentina. Contradicting the original description of this species and its generic diagnosis, all specimens had 5 loculi (2 anterior plus 3 posterior loculi) plus 5 corresponding haptoral septa only (central loculus absent). The original description of this species erroneously specified 6 loculi, including 2 small anterolateral loculi. Because A. dischizosepta was the type species for Tetrasepta Suriano, 1975 and because it fits the diagnosis of Allobenedenia Yamaguti, 1963, the genus therefore is regarded a junior synonym of Allobenedenia. Allobenedenia dischizosepta differs from its congeners by lacking a haptoral peduncle as well as by having 5 haptoral loculi, accessory sclerites that lack a conspicuous dorsal protuberance and that are weakly bifid, by posssesing robust anterior hamuli that are strongly recurved for half of their total length, by having a male accessory gland reservoir in the extreme posterior portion of the penis sac and lateral to the vitelline reservoir abutting the ovary, and by the presence of a straight (not coiled) proximal portion of the ejaculatory duct within the penis sac.