THE radio source G318.9 + 0.4 has been tentatively identified as a supernova remnant (SNR)1,2. Here I report observations at 843 MHz revealing a remarkable network of arcs in the object which exclude it from any of the standard classes of SNRs. The arcs outline an approximately elliptical region enclosing a bright off-centre core component which has several curved extensions. Although the appearance of the arc structures is unprecedented, G318.9 + 0.4 might belong to a recently proposed class of non-thermal axisymmetric radio sources unrelated to SNRs3. Alternatively, the core component may indeed be a SNR, excited by the stellar remnant of the supernova event, with the arc emission arising through jet activity.