Yunnanozoon lividum is a suspected a hemichordate

Hemichordata

Hemichordata is a phylum of marine deuterostome animals, generally considered the sister group of the echinoderms. They date back to the Lower or Middle Cambrian and include two main classes: Enteropneusta , and Pterobranchia. A third class, Planctosphaeroidea, is known only from the larva of a...

 or chordate

Chordate

Chordates are animals which are either vertebrates or one of several closely related invertebrates. They are united by having, for at least some period of their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail...

 from the Lower Cambrian

Cambrian

The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

, Chengjiang biota of Yunnan

Yunnan

Yunnan is a province of the People's Republic of China, located in the far southwest of the country spanning approximately and with a population of 45.7 million . The capital of the province is Kunming. The province borders Burma, Laos, and Vietnam.Yunnan is situated in a mountainous area, with...

 province, China

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

.

Yunnanozoon is similar to the form Haikouella

Haikouella

Haikouella is a probable chordate from the Lower Cambrian Maotianshan shales of Chengjiang County in Yunnan Province, China.It is similar to the form Yunnanozoon, which is possibly a hemichordate. Still, there are anatomical differences from Yunnanozoon, including a larger stomach and smaller ...

which is almost certainly a chordate. Still, there are anatomical differences from Haikouella, including a smaller stomach

Stomach

The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...

 and much larger (1 mm) pharyngeal teeth

Pharyngeal teeth

Pharyngeal teeth are teeth in the pharyngeal arch of the throat of cyprinids, suckers, and a number of other fish species lacking teeth.Popular aquarium fish such as goldfish and loaches have these structures. Members of the Botia genus such as clown loaches are known to make distinctive clicking...

. Yunannozoon is not known for sure to possess many features like heart

Heart

The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

, gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s, etc. that are known from well preserved specimens of Haikouella

Haikouella

Haikouella is a probable chordate from the Lower Cambrian Maotianshan shales of Chengjiang County in Yunnan Province, China.It is similar to the form Yunnanozoon, which is possibly a hemichordate. Still, there are anatomical differences from Yunnanozoon, including a larger stomach and smaller ...

. Yunnanozoon somewhat resembles the Middle Cambrian Pikaia

Pikaia

Pikaia gracilens is an extinct animal known from the Middle Cambrian Burgess Shale of British Columbia. -Discovery:It was discovered by Charles Walcott and was first described by him in 1911. It was named after Pika Peak, a mountain in Alberta, Canada. Based on the obvious and regular segmentation...

from the Burgess shale

Burgess Shale

The Burgess Shale Formation, located in the Canadian Rockies of British Columbia, is one of the world's most celebrated fossil fields, and the best of its kind. It is famous for the exceptional preservation of the soft parts of its fossils...

 of British Columbia

British Columbia

British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

 in Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

. Thirteen pairs of symmetrically arranged gonad

Gonad

The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...

s have been identified, as have possible gill slits. However, some authors think that Yunnanozoon is closely related to the chordate Haikouella and that Yunnanozoon is probably a chordate rather than a hemichordate. A close relationship between Yunnanozoon and the phylum Vetulicolia

Vetulicolia

VetulicoliaThe phylum name, Vetulocolia, is derived from the type genus, Vetulicola, which is a compound Latin word composed of vetuli, or "old," and cola, or "inhabitant." is an extinct phylum encompassing several Cambrian organisms...

has also been proposed.