Chordates

A chordate ( ) is a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (synapomorphies) that distinguish them from other taxa: a notochord, a hollow dorsal nerve cord, an endostyle or thyroid, pharyngeal slits, and a post-anal tail.

Olfactores is a clade within the Chordata that comprises the Tunicata (Urochordata) and the Vertebrata (sometimes referred to as Craniata). Olfactores represent the overwhelming majority of the phylum Chordata, as the Cephalochordata (with only 32 known species across 3 genera) are the only chordates not included in the clade. This clade is defined by a more advanced olfactory system which, in the immediate vertebrate generation, gave rise to nostrils.

Yunnanozoon lividum (from Yunnan, and Ancient Greek ζῷον (zôion), meaning "animal", with specific name coming from Latin lividum; (lead-coloured), referring to preserved colour of specimens) is an extinct species of bilaterian animal from the Lower Cambrian Chengjiang biota of Yunnan province, China. Its affinities have long been the subject of controversy.