Editing Chordate (section)

==Closest non-chordate relatives==
[[File:Enteropneusta.png|thumb|Acorn worms or Enteropneusts are example of hemichordates.]]
The closest relatives of the chordates are believed to be the [[hemichordate]]s and [[Echinodermata]], which together form the [[Ambulacraria]].
The Chordata and Ambulacraria together form the superphylum [[Deuterostomia]]. 

===Hemichordates===
{{main|Hemichordate}}

[[Hemichordate]]s ("half chordates") have some features similar to those of chordates: branchial openings that open into the [[pharynx]] and look rather like gill slits; stomochords, similar in composition to [[notochord]]s, but running in a circle round the "collar", which is ahead of the mouth; and a [[dorsa]]l nerve cord—but also a smaller [[ventral]] nerve cord.

There are two living groups of hemichordates. The solitary [[enteropneust]]s, commonly known as "acorn worms", have long [[proboscis]]es and worm-like bodies with up to 200 branchial slits, are up to {{convert|2.5|m|ft}} long, and burrow though [[seafloor sediment]]s. [[Pterobranch]]s are [[colony (biology)|colonial]] animals, often less than {{convert|1|mm|in}} long individually, whose dwellings are interconnected. Each [[filter feeding|filter feeds]] by means of a pair of branched tentacles, and has a short, shield-shaped proboscis. The extinct [[graptolite]]s, colonial animals whose fossils look like tiny [[hacksaw]] blades, lived in tubes similar to those of pterobranchs.<ref>{{cite web|url=http://www.ucmp.berkeley.edu/chordata/hemichordata.html|access-date=2008-09-22|title=Introduction to the Hemichordata|publisher=University of California Museum of Paleontology|archive-url=https://web.archive.org/web/20190201080336/http://www.ucmp.berkeley.edu/chordata/hemichordata.html|archive-date=1 February 2019}}</ref>

===Echinoderms===
[[File:Estrella de mar de espinas rojas (Protoreaster linckii), Zanzíbar, Tanzania, 2024-06-01, DD 06.jpg|thumb|203x203px|A red knob sea star, ''[[Protoreaster linckii]]'' is an example of an [[asterozoa]]n [[echinoderm]].|right]]
{{main|Echinoderm}}
[[Echinoderm]]s differ from chordates and their other relatives in three conspicuous ways: they possess [[bilateral symmetry]] only as larvae – in adulthood they have [[radial symmetry]], meaning that their body pattern is shaped like a wheel; they have [[tube feet]]; and their bodies are supported by [[dermal]] [[skeleton]]s made of [[calcite]], a material not used by chordates. Their hard, calcified shells keep their bodies well protected from the environment, and these skeletons enclose their bodies, but are also covered by thin skins. The feet are powered by another unique feature of echinoderms, a [[water vascular system]] of canals that also functions as a "lung" and surrounded by muscles that act as pumps. [[Crinoid]]s are typically [[sessility (motility)|sessile]] and look rather like flowers (hence the [[common name]] "[[sea lilies]]"), and use their feather-like arms to filter food particles out of the water; most live anchored to rocks, but a few species can move very slowly. Other echinoderms are mobile and take a variety of body shapes, for example [[starfish]] and [[brittle star]]s, [[sea urchin]]s and [[sea cucumber]]s.<ref name="CowenHistLifeEd3P412">{{cite book
| author=Cowen, R. | title=History of Life | year=2000 | page=412
| publisher=Blackwell Science | edition=3rd | isbn=978-0-632-04444-3
}}</ref>