Middle Ordovician extinctions

Asaphus () is a genus of trilobites that is known from the Lower (upper Arenig) and Middle Ordovician of northwestern Europe (Sweden, Estonia, Saint Petersburg Area).

Agnostidae is a family of Agnostida trilobites. Like all Agnostina, they were eyeless and had only two thoracic segments. These trilobites inhabited benthic waters worldwide from 508 to 461 million years ago. The family includes the following genera, among others:

Hazelia is a genus of spicular Cambrian demosponge known from the Burgess Shale, the Marjum formation of Utah, and possibly Chengjiang. It was described by Charles Walcott in 1920.

Astraspida, or astraspids, are a small group of extinct armored jawless vertebrates, which lived in the Late Ordovician (about 450 million years ago) in North America. They are placed among the Pteraspidomorphi because of the large dorsal and ventral shield of their head armor. They are represented by a single genus, Astraspis, including possibly two species, A. desiderata and A. splendens but their remains are fairly abundant in Ordovician sandstones of the USA (Colorado, Arizona, Oklahoma, Wyoming) and Canada (Quebec). The head armor of Astraspis is rather massive, with a series of ten gill