- Source: Calveriosoma hystrix
Calveriosoma hystrix is a species of sea urchin of the family Echinothuriidae. Their armour is covered with spines. Calveriosoma hystrix was first scientifically described in 1872 by Thomson. C. hystrix has a structure known as a siphon, which is a thin tube that runs parallel to the stomach. While its function is not certain, it likely serves a way of moving water from the esophagus to the beginning of the intestine.