A re-evaluation of the Ordovician cystoid Stichocystis Jaekel and the taxonomic implications

Stichocystis is re-described. The genus is a rhombiferan with exothecal pore structures developed in a rhomb-in-rhomb pattern with canals embedded within narrow calcite ridges. The pore system developed by regular addition of new sutural pores which later in ontogeny became separated by a calcite ridge as the canal grew outwards from the suture. This type of pore structure is highly specialized. The plate configuration of the oral-anal area clearly puts Stichocystis amongst the Caryocystitidae and close to the genera Heliocrinites and Lophotocystis with which it shares many characteristics. The two orders of the Rhombifera, the Dichoporita and the Fistuliporita reflect two fundamentally different types of pore structures, endothecal and exothecal. With regard to these structures, the order Fistuliporita is more closely related to the Class Diploporita than to the Dichoporita.