Arpylorus antiquus, erected by Calandra in 1964, was isolated from upper Silurian sedimentary rocks from the Mechiguig 1 borehole in southern Tunisia, with other palynomorphs. The folded vesicle and the quadrangular form of the aperture break down into platelike fragments, resembling the tabulation of dinoflagellates. The presence of these elements has been used to interpret A. antiquus as a dinoflagellate cyst. The morphology and affinity of A. antiquus is reinterpreted herein based on investigation of larger sets of samples, including material from the type locality, together with material of Algeria, Saudi Arabia, and Brazil. More complete specimens than those previously described have been observed using gentle laboratory techniques, showing a large development of a fine membrane at the periphery of vesicles. This element was destroyed using classical palynological treatments, implying that the holotype is an incomplete specimen. The membrane at the periphery of vesicles and dorsoventral differentiation of these vesicles suggest that A. antiquus is a part of a more complex biological structure. We suggest a possible relationship with eurypterids, arthropods related to phyllocarids, represented by abundant fragments in the assemblages. Arpylorus antiquus is possibly a structure of storage. The chemical composition of A. antiquus using a Fourier transform infrared FTIR microspectroscopy analysis, reveals a wall composed of biopolymer that is not consistent with dinosporin. We conclude that Arpylorus antiquus is definitively not a dinoflagellate cyst. Although dinoflagellates may have older Paleozoic or even Proterozoic ancestors as the biomarker record may suggest, the dinoflagellate tabulation evolved only in the early Mesozoic.