Cidaridae Family of Pencil Urchins
Three Pencil Urchins of the Cidaridae Family can be found in this website:
Phylogeny: Pencil Urchins are a member of the Cidaridae Family. Like Starfish and Sea Cucumbers they belong to the phylum Echinodermata. They are in the class Echinodea and the order Cidaroida. The order Cidaroida is the most primitive of the sea urchin orders. The Cidaridae Family is comprised of four subfamilies, one tribe, thirty-one genera, and one hundred eight species. The name Cidaridae comes from the New Latin word for “tiara” or “headdress”.
Morphology: Pencil Urchins have stout tests that are composed of 20 columns of overlapping plates (ossicles). Cidarids are covered by movable spines with the spines being more widely spaced than their sea urchin cousins. The primary tubercles are perforate, not crenulate. The spines may be conical, thorn-like, or club shaped. They are characterized by a larval stage with bilateral symmetry and an adult stage with 5-rayed radial symmetry. They have a water vascular system, tube feet, and a complete digestive system, but they lack a head, eyes, nervous system, or excretory system. There are tiny pincers (pedicellariae) located between the spines. Their mouth is located on the flat, or concave, underside. Inside the mouth is a complex chewing apparatus, made of 5 jaws, that is known as an Aristotle’s Lantern. They move by the use of tube feet and by moving their spines. The largest Pencil Urchins reach a maximum of 30 cm (12 inches) in diameter.
Distribution: Pencil Urchins are found in crevasses on rock or coral, or on sand or mud. They range in depth from the intertidal zone to depths over 3,000 m (9,840 feet). Pencil Urchins are found worldwide in tropical to polar seas. Five species from the Cidaridae Family are found in Mexican waters.
Reproduction: Pencil Urchins are gonochoric and reproduction occurs via broadcast spawning where the females release hundreds of thousands of eggs into the surrounding water concurrently with the release of sperm by males. The gametes become planktonic larvae before attaching to substrate. Some species brood their young.
Ecosystem Roles: Cidarids are omnivores that feed on bryozoans, detritus, foraminifera, sea grass, and sponges. Pencil Urchins utilize their colors for camouflage and their barb-laden spines for protection, but they are preyed upon by triggerfish, various species of wrasse, and other fishes. Cidarids host a variety of epibionts. Crabs, polychaetes, brittle stars, algae, encrusting organisms, and fish all find a stable substrate and a safe microhabitat among the urchin spines.