The Echinoid Directory

Lantern Structure

The lantern is composed of 50 skeletal elements and surrounds the entrance to the stomach. The lantern of a cidarid is seen here in aboral and lateral views. The largest elements are the hemipyramids (h). These are paired wedge-shaped plates firmly bound together interradially to form the five pyramids of the lantern. There is a notch between the two hemipyramids at the adapical end of their suture, this is the foramen magnum (fm). The foramen magnum is small in cidaroids, but is typically very deep and V-shaped in other regular echinoids. The adapical shoulder of each hemipyramid houses a small axe-shaped element, the epiphysis (e). In a radial position there is a single tongue-shaped element, the rotula (r), which rests directly on two epiphyses, one from each adjacent pyramid. The rotula acts as a brace binding adjacent hemipyramids together. A single tooth (t) lies interradially abutting the interior of each hemipyramid and is generally visible through the foramen magnum. Finally, there are narrow, spatula-shaped elements, the compasses (c), that overlie each rotula. The compasses function to raise and lower the walls of the lantern coelom as the lantern is moved in and out of the test during feeding. The muscle attachment platforms that form the perignathic girdle (g) around the peristome are visible at the base.