A very nice Walliserops issimourensis and Ptychopariida from Atchana Morocco with perfect details. Walliserops is one of the rarest species of trilobites, ads is exceptional to find it in the same matrix with another trilobite. These are an extinct arthropod belonging to the trilobites. It lived in the Lower Devonian (about 400 million years ago). Its remains have been found mainly North Africa. Trilobites (meaning "three-lobed entities") are extinct marine arthropods that form the class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most successful of all early animals, existing in oceans for almost 270 million years, with over 22,000 species having been described.