Cidaridae

Cidaridae is a family of sea urchins, commonly known as slate pencil urchins or pencil urchins. These echinoderms are distinguished by their exceptionally long, stout, and often brightly colored spines. Unlike many other sea urchin families where the spines are relatively short and thin, the spines of Cidaridae are thick and have a calcareous, porous structure, giving them a resemblance to pencils or chalk. The apical system, which includes the anus and madreporite, is typically large and prominent.

The family Cidaridae is diverse, with numerous genera and species found in marine environments worldwide, from shallow coastal waters to the deep sea. They inhabit a variety of substrates, including rocky reefs, coral, and soft sediments. Their diet consists primarily of algae, but some species may also consume sessile invertebrates or detritus. The robust spines serve as a primary defense mechanism against predators. Reproduction in Cidaridae, as with other sea urchins, involves the external release of eggs and sperm, with planktonic larvae developing before settling to the seabed. Fossil evidence suggests that Cidaridae is one of the oldest extant families of sea urchins, with a lineage dating back to the Jurassic period.