Ptychagnostus

Ptychagnostus is a member of the agnostida that lived during the Cambrian period. Ptychagnostidae generally do not exceed one centimetre in length. Their remains are rarely found in empty tubes of the polychaete worm Selkirkia. The genus probably ranged throughout the water column. It has two glabellar lobes, and three pygidial lobes.

Type species
Agnostus punctuosus Angelin, 1851 from the Pt. punctuosus Zone of the Alum Shale (Drumian), Sweden (by original designation). Official ruling on the conservation of accepted usage of A. punctuosus as the type species was given by the International Commission on Zoological Nomenclature, 1993.

Remarks
Ptychagnostus affinis (Brøgger 1878) was once considered a subspecies of Pt. punctuosus. Laurie (2008) grouped punctuosus and affinis within Ptychagnostus, but preferred to place the closely related atavus within Acidusus.

Ptychagnostidae Genera
Høyberget & Bruton (2008) concluded that the following genera belong in the Ptychagnostidae: Ptychagnostus, Goniagnostus, Tomagnostus, Lejopyge, Aotagnostus and Onymagnostus.

Species

 * Ptychagnostus punctuosus (Type species).
 * Ptychagnostus affinis (formerly Pt. punctuosus affinis)
 * Ptychagnostus aculeatus
 * Ptychagnostus akanthodes
 * Ptychagnostus atavus
 * Ptychagnostus cassis
 * Ptychagnostus ciceroides
 * Ptychagnostus cuyanus
 * Ptychagnostus germanus
 * Ptychagnostus gibbus
 * Ptychagnostus hybridus
 * Ptychagnostus intermedius
 * Ptychagnostus michaeli
 * Ptychagnostus praecurrens
 * Ptychagnostus seminula