Agnostid trilobite Glyptagnostus reticulatus. Glyptagnostus reticulatus is a species of trilobite belonging to the order Agnostida. Trilobites were arthropods that fed as they crawled on the seabed. Glyptagnostus reticulatus was widespread in the Cambrian Period around 497 million years ago. It was characterized by the unusual pattern of furrows on its head and posterior segment. It was completely blind and had only two thoracic segments. It is an important index fossil, used in geology and palaeontology to define and identify the beginning of the Paibian Age of the Cambrian Period.