Large acritarchs were recovered from the Awaynat Wanin II Formation in the A1-69 borehole, western Libya at 394.4 m. This sample has been dated by acritarchs and spores as Givetian (Middle Devonian). Two species of acanthomorph acritarchs were recovered that are unusually large for the Paleozoic. The first type, represented by a single specimen, is a new occurrence of a previously described but unnamed form from the Middle Devonian of the Sahara. The second type, which is more abundant, is named as Vanguestainidium cucurbitulum gen. et sp. nov. Biogeochemical analysis using infrared microspectroscopy shows that the wall composition of this new taxon is close to algaenans isolated from the green alga Botryococcus brauniiKützing 1849 although these forms are not morphologically similar. The presence of well-preserved fragile palynomorphs, abundant terrestrially-derived palynomorphs including large megaspores, and rare marine palynomorphs suggests deposition in a low-energy nearshore environment such as a coastal swamp.