Echinometridae Family of Sea Urchins
Van Brunt’s Sea Urchin, Echinometra vanbrunti. A representative of the Echinometridae Family of Sea Urchins.
Phylogeny: Sea urchins of the Echinometridae Family, like starfish and sea cucumbers, are in the phylum Echinodermata. They are in the class Echinoidae, the subclass Euechinoidea, the infraclass Carinacea, the subterclass Echinacea, the order Camarodonta, and the infraorder Echinidea. The Echinometridae Family is one of three families in the superfamily Odontophora. The Echinometridae Family contains nine genera and around twenty-four species. The name Echinometridae comes from the Greek words meaning “spiny measure”, perhaps referring to the length of the spines.
Morphology: These sea urchins that they have an internal skeleton (test) made of overlapping plates (ossicles). Their tests are covered by moveable spines. The spines are roughly as long as the test diameter. The spines may be pointed, flattened, or club-like. There are tiny pincers (pedicellariae) located between the spines. These urchins generally have an asymmetric lateral tooth on the blade of their globiferous pedicellariae. Less noticeable are the imperforate tubercles and compound ambulacral plates. Their mouth is located on the flat, or concave, underside. Inside the mouth is a complex chewing apparatus, made of five jaws, that is known as an Aristotle’s Lantern. They move by the use of tube feet and by moving their spines. They have a water vascular system, tube feet, and a complete digestive system, but they lack a head, eyes, nervous system, or excretory system. Sea urchins of the Echinometridae Family are found in a variety of colors including black, green, purple and white. They have tests that reach a maximum of 8.0 cm (3.1 inches) in diameter.
Distribution: Echinometridae sea urchins are normally found on coral or rocks but also may be found on mud, rubble or sand substrates. The majority of the members of the Echinometridae Family are found at depths less than 30 m (98 feet), but some exceed 140 m (460 feet). They are distributed worldwide in tropical and sub-tropical seas. At least four species from this family are found in Mexican waters.
Reproduction: Echinometridae sea urchins are gonochoric (male or female for life). They reproduce sexually through broadcast spawning, with external fertilization. The fertilized eggs hatch into planktonic larvae and pass through several larval phases before settling to the bottom as juvenile urchins.
Ecosystem Roles: Echinometridae Sea Urchins are primarily nocturnal. They may be herbivorous grazers or depositional omnivores. They feed on algae, detritus and sea grasses. In turn they are preyed upon by brittle stars, fish, gastropods and sea stars. Some species in this Family are Rock-boring Urchins. Rock-boring Urchins use their teeth to dig a depression into the rock surface to help protect them from certain predators as well as extreme water movement. They usually leave their hole at night to feed. In some cases they dig such a deep hole that they can no longer leave. When that happens, they feed on algae that grows in the hole and larger algae that are moved into the hole by currents. These holes can become microhabitats, and are often shared by other species.
A Word of Caution! Sea Urchins of the Echinometridae 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.