Clades:
Deuterostomia.
Genera: 71 species.
Habitat: marine.
ZoologyHemichordata are worm-shaped marine animals. They have a primitive notochord, formed from a diverticulum of the foregut called a stomochord, a hollow neural tube exists among some species at least in early life.
Their bodies are divided into three parts: proboscis, collar and trunk.
They have open circulatory systems and a complete digestive tract but the musculature in their gut is very poorly developed, and food is mostly transported through it by using the cilia that cover its inside surface.
CladesEnteropneusta: acorn worms.
Pterobranchia: include the graptolites.
Planctosphaeroidea.
TaxonomyThe exact taxonomic position of
Hemichordata and whether the group is monophyletic is currently under debate. One of the suggestions is that the pterobranchs are more basal deuterostomes, while the enteropneusts are an early offshoot of the lineage who are leading to
Chordata.