Astraspids are thought to have been about 7.9 inches in length. They are also thought to have had a mobile tail covered with small protective plates of less than 0.039 inches and a head region covered with plates larger than 0.079 inches. The specimen from North America is thought to have had relatively large, lateral eyes and a series of eight gill openings on each side. The specimen was generally oval in cross-section. The protective bony plates covering the animal were composed of aspidin (chemically similar to modern shark's teeth), covered by tubercles composed to dentine. It is from these tubercles (which are generally star-shaped) that the name 'Astraspis' is derived.