Horse dung sea urchin fossils

The horse dung sea urchin shell is sturdy, hemispherical in shape, with a diameter of 30-40 millimeters and a maximum of 60 millimeters. The opposite side of the mouth is low, slightly raised, and the mouth surface is flat. The width of the step zone is equal to that of the intermediate step zone, but the swelling degree of the intermediate step zone is slightly higher than that of the step zone. Therefore, the shell shape appears as a smooth regular pentagon that is close to a circular shape when viewed from the mouth. The activity of sea urchins relies on the movement of their tubular feet and spines to crawl on the seabed, so their movement speed is relatively slow. Sometimes, they adsorb onto rocks through tubular suction cups. The horse dung sea urchin is usually considered a herbivorous animal that feeds on brown algae, red algae, and green algae. It mainly lives on the seabed of shallow waters such as rocks, gravel, and sand.