336 Review of selected North American mitrate stylophorans

This paper reviews most of the North American mitrate stylophoran genera and species that are assigned to two suborders, the Anomalocystitida and the Peltocystida. The Anomalocystitida is herein divided into two long-ranging families, the Anomalocystitidae and the Placocystitidae. The Anomalocystitidae contains mostly North American species (Middle Ordovician-Early Devonian) that are characterized by the proximal carapace margin having three plates, and only very rarely a placocystitid plate. 

The feeding strategies of mitrates are seen to be different than previously reported. In mitrates, the aulacophore faced into the prevailing current, convex upward, and food was conveyed to the food groove under the dorsally-fused cover plates through the arcuate to chevron-shaped openings between the overlapping set of cover plate pairs. The width of these openings was controlled by the degree of distal aulacophore convexity. Previous representations of feeding figured the distal aulacophore concavely curved over the proximal aulacophore and proximal theca. 

Origin of the Anomalocystitida derives from Reticulocarpos-like comutans. It is suggested that the distal marginal plate elements of the theca in the comute ancestral stock have been lost. Only M1-M4 thecal marginals are homologous between comutes and anomalocystitids.
     

Year published: 1991