Micromorphology of the Aristotle's Lantern in the Sand Dollar, Scaphechinus mirabilis (Echinoidea: Echinolampadacea): Insights from Scanning Electron Microscopy and Three-Dimensional X-Ray Microscopy.

The morphology and micromorphology of Aristotle's lantern, the feeding apparatus of Scaphechinus mirabilis, were examined using light microscopy, scanning electron microscopy, and X-ray microscopy. S. mirabilis had food grooves on the ventral side, which extended to the mouth. Aristotle's lantern was a star-shaped calcareous skeletal structure attached to the test by the apophysis and consisted of pyramids, joints, and teeth. The pyramid consisted of two demi-pyramids, an epiphysis, and a bump, whereas the joint located between the pyramids consisted of the interpyramidal ligament and rotula. The tooth was an elongated trapezoid with one pointed end (3.98 × 0.97 × 0.38 mm) and was divided into an embedded part and a projection part. The embedded part was connected to the dental ligament and dental promoter muscle, whereas the projection part was divided into a basal projection part covered by the peridental membrane and an apical projection part protruding beyond the tooth slide. The tooth exhibited a calcareous lamellar structure composed of 15-20 layers, and its distal end was worn. These findings indicate that the morphology of the tooth is specialized for internal crushing of sediment and food particles within the Aristotle's lantern.