|The fossil of Helicocystis moroccoensis|
Named Helicocystis moroccoensis, it was just four centimetres high and had a cigar-shaped body composed of a calcite skeletal lattice supporting a calyx of checkered plates, with a short stem at the bottom and a mouth at the top. Based on its physiology, it would have been able to expand and contract, thus making itself larger than its fossilized four centimetres.
What makes it important is that it lies between pentaradial sea urchins and the first echinoids on the planet. The oldest known echinoderm, a creature from the White Mountains in California named Helicoplacus, had a spiral body but was asymmetrical in form. Helicocystis also has a spiral body by pentaradial symmetry. What is interesting is that all echinoids develop from a bilateral larva rather then possessing the adult form of symmetry from birth.
|Helicocystis moroccoensis, the oldest sea urchin with|
pentaradial symmetry, coming in at 520 million years old
Echinoids and the wider group of the echinoderms which includes sand dollars and starfish have been highly succesful since they first evolved. They appear all through the fossil record, a diverse panoply of forms which have endured throughout hundreds of millions of years, a story whose origins and success can be traced all the way back to Helicocystis. The next task is to pin down exactly where, in the first instance, echinoids came from.