Graptolites are tiny extinct hemichordates animals.  They lived in colonies and are used for geological unit description. Some colonies grew like tree's branches  some has spiral shape and some oders as a strange U horse shoes plint. the most curious have a spiral-shaped. We love them.
Check our graptolites for sale.
 
 
Tetragraptus tridens
Ordovician
Chewtonian fm
Spring Gully
Bendingo
Victoria Australia