Unlike a Corona, it also has a set of radial ridges which arc away from the fault ring. It is also much smaller than most coronas. In this case, the fault ring is about 95 km across, and most arachnoids are about the same size. In contrast, most coronas are over 200 km across. Still, outside the fault ring, the ridges seem to run 100 to 200 km before merging with other ridge systems.
Most arachnoids show few signs of volcanism.
Here, there are a few small shields in the center, but the plains lavas show the clearest signs of volcanism. Note the bright lava flows on the northwest and southeast that seem to come out of the fault ring. These all suggest that many large, thin lava flows were erupted as the arachnoid was forming. Complex Arachnoids Arachnoids often lie in faulted plains, and their outer ridges tend to turn into regional patterns. Thus, they often look like spiders on a bright web.