An emendation of the generic diagnosis of Phoreiobothrium Linton, 1889 (Tetraphyllidea: Onchobothriidae) with a detailed description of bothridia and hooks

Abstract

Hook terminology for the three-pronged hooks of Phoreiobothrium Linton, 1889 is reconciled with that for two-pronged hooks such that the two outermost prongs are considered homologous with the prongs of a two-pronged hook and the third inner prong is termed the basal prong. Scanning electron microscopy was performed on the scolex of Phoreiobothrium lasium Linton, 1889 and the solid nature of the bothridia was reconfirmed. Examination of material of all four species of Phoreiobothrium leads to the conclusion that each species possesses three-pronged hooks that are hollow and open to the outside via pores. The bothridia of each species are considered to be horizontally divided into two loculi, the posterior one being recessed and vertically subdivided. The diagnosis of the genus Phoreiobothrium is emended, and the four species allocated to it are redescribed. Phoreiobothrium is determined to be a monophyletic group on the basis of two synapomorphies and a key to the four species of the genus is presented.