|A hand specimen of siltstone rock from the Llajas Formation has three specimens of |
S. diabloensis on the same bedding plane. The hand specimen is 5 cm (2 in.) wide.
|Five specimens of S. diabloensis from the Llajas Formation. The largest specimens are|
2 cm (0.8 in.) wide. All are top-side up.
You can readily see the five-rayed symmetry of the feeding grooves on the dorsal (top) surface of each specimen. The central groove, called ambulacrum III, is the longest and is sunken on most spatangoids, whereas the two posterior grooves are smaller.