These possess a symmetry based on five, which is extremely rare in nature, as
most animals have a binary symmetry, meaning that, if they are cut down the middle,
two identical parts can be observed. This is not possible with echinoderms, because
they have to be cut into five sections to obtain identical pieces. Echinoderm means
spiny skin: this is highly appropriate in the case of sea urchins, less so in relation
to the rough starfish. Generally speaking, echinoderms will not survive for long
outside water. They are found only in sea water.