CARPOIDS are bizarre, extinct invertebrates called echinoderms (living examples are starfish, sea urchins and sea lilies).  They first appeared in the fossil record in the Cambrian Period with some types surviving into the Carboniferous Period.  They are an enigma to scientists and much has yet to be learned as to exactly how these creatures lived.  Unlike other echinoderms they are grouped with, they lack radial symmetry and an obvious hydrovascular system.  Like all echinoderms, Carpoids possess a calcite skeleton made up of plates in a three-dimensional mesh called a stereom.  

Currently, Carpoids are classified into 4 major types - CTENOCYSTOIDS (Middle Cambrian Period), CINCTANS (Middle Cambrian Period), SOLUTES  (Middle Cambrian to Lower Devonian Period) and STYLOPHORANS  (Middle Cambrian to Upper Carboniferous Period).