Diadematidae Family of Sea Urchins
Two Sea Urchins of the Diadematidae Family can be found in this website:
Phylogeny: Diadematid Sea Urchins of the Diadematidae Family, like sea stars and sea cucumbers, belong to the phylum Echinodermata. They are in the class Echinoidea, the subclass Euechinoidea, and infraclass Aulodonta, the superorder Diadematicea, and the the order Diadematoida. The Diadematiadae Family is one of two families in this order. The Diadematiadae Family contains ten genera and around forty species. Species in this family are also commonly call Diadematids. The name Diadematidae comes from the Greek word for “diadem” or “headband”, which refers to the long spines resembling a royal headdress.
Morphology: Diadematidae Sea Urchins have an internal skeleton (test), made of overlapping plates (ossicles), that is globular in shape. The outer surface is covered by moveable spines. These spines are long, hollow, and brittle. They have tiny pincers (pedicellariae) between their spines. The underside may be flat or concave. Their mouth is located in the center of the underside. Inside the mouth is a complex chewing apparatus, made of five jaws, that is known as an Aristotle’s Lantern. They have a water vascular system, tube feet, and a complete digestive system, but they lack a head, eyes, nervous system, or excretory system. They move by the use of tube feet and by moving their spines. They have light sensitive organs, enabling to point their spines toward a potential predator. Their larval stage has bilateral symmetry; the adult stage has 5-rayed radial symmetry. Sea Urchins in the Diadematidae Family may be black, blue, green, red or purple in color. Their tests vary in diameter from around 5 cm (1.9 inches) to 20 cm (7.9 inches). The spines can reach a maximum of 38 cm (15 inches) in length.
Distribution: Diadematid Sea Urchins may be found on coral, rock, mud, or sand substrates. They live from the intertidal zone to depths that exceed 5,000 m (16,400 feet). They are found worldwide in tropical to polar seas. At least five species from this family are found in Mexican waters.
Reproduction: Sea Urchins are gonochoric (either male or female for life). They reproduce sexually, through broadcast spawning, with external fertilization. The fertilized eggs develop into planktonic larvae before settling to the substrate to metamorphose into a juvenile sea urchin.
Ecosystem Roles: Diadematid Sea Urchins may be herbivores or omnivores. They feed by scraping or chewing on a variety of foods including algae, bryozoans, carrion, coral polyps, detritus, sea grasses, and other sessile animals. In turn they are preyed upon by shore birds, crabs, fish, marine mammals and sea stars. Sea Urchins of the Diadematidae Family are not venomous, but should be handled with care because the spines are sharp, will break off in the skin, can be very painful to humans, and are exceedingly difficult to remove.