Arachnoids are surface features of the Venusian surface that exhibit circular characteristics such as concentricity, extruding radial fractures, with ridges and valleys. These arachnoids range in size from 50 kilometers (29.9 miles) to 230 kilometers (137.7 miles) in diameter. They resemble to a degree volcanoes and as one theory suggests, they are a precursor to coronae formation. The radial fractures seen in the structure may have been the result of internal pressure.
Arachnoids 
