The starfish is one of the most curious of sea creatures. Among its queer relatives are the prickly sea-urchins, the sea cucumbers, and the sand dollars. There are more than 6,000 of these relatives and they are called “echinoderms,” which means spiny-skinned.

The starfish and its relatives all have well-developed nervous and digestive systems. This system follows the same five-armed arrangement which occurs in all echinoderms.