This is an eleven-armed starfish, also known as a spiny star, Coscinasterias calamaria, or papatangaroa. They can reproduce both sexually (with eggs and sperm) and asexually (by division) and eat shellfish by wrapping themselves around their prey, levering open the shell and etruding their stomach inside out onto their prey. Starfish are supposedly about 90% water and up to 6 or 8% chalk.
