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

Abstract

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.