Slate pencil urchin explained

Slate pencil urchin (named after slate pencil) is a common name for several sea urchin species with blunt spines:

• Eucidaris, a genus with several tropical species, especially:
  • Eucidaris thouarsii, an East Pacific species
  • Eucidaris tribuloides, an Atlantic species
• Heterocentrotus, a genus with two Indo-Pacific species