The Echinoid Directory

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Lantern and girdle

The most specialised and modified lanterns of all echinoids are to be found in the sand dollars. They are composed of almost all of the same elements as in regular echinoids (only compasses are absent) but are extremely low and wide by comparison. The hemipyramids (H) are highly flattened, deltoid in outline and have no foramen magnum. Teeth (T) are diamond-shaped in cross-section and steeply sloping. Epiphyses and rotulae are reduced to tiny disc-like elements that are largely hidden from sight in between the hemipyramids (in the position marked (R/E).

The perignathic girdle marks the site of attachment for lantern muscles. In clypeasteroids it consists of a ring of peg-like projections. These arise from the single interambulacral plates in the Scutellina (pictured above - G), but are paired ambulacral structures in Clypeasterina. Cassiduloids lack a lantern, and thus have no perignathic girdle as adults.

The lantern cannot be protruded from the mouth and is used solely for chopping and cutting material that is taken in through the peristome. As it is never protruded there is no need for pharyngeal sacs or buccal notches.

The lantern illustrated is from Laganum and is shown in top (internal) and side views.