A part of the ventral disc of Giardia species (trophozoite stage) consisting of a spiral array of microtubules linked to the ventral membrane. These microtubules form the base of the ventral disc dorsal microribbons that extend nearly perpendicular from the membrane.
Comment:
Due to the asymmetric nature of the Giardia trophozoite, this term is defined spatially as the trophozoite is viewed from the dorsal side, with the two nuclei dorsal to the ventral disc, and the ventral disc toward the anterior.