Editing Chordate (section)

===Tunicata (Urochordata)===
{{main|Tunicate|l1= Tunicate (Urochordata)}}

[[File:BU Bio.jpg|thumb|right|Tunicates: sea squirts]]

The [[tunicates]] have three distinct adult shapes. Each is a member of one of three monophylitic clades. All tunicate [[larva]]e have the standard chordate features, including long, [[tadpole]]-like tails. Their larva also have rudimentary brains, light sensors and tilt sensors.<ref name="Benton2002VertebratePalaeontologyP5" /> 

The smallest of the three groups of tunicates is the [[Larvacean|Appendicularia]]. They retain tadpole-like shapes and active swimming all their lives, and were for a long time regarded as larvae of the other two groups.<ref>{{cite web| title=Appendicularia| publisher=Australian Government Department of the Environment, Water, Heritage and the Arts| url=http://www.environment.gov.au/biodiversity/abrs/publications/electronic-books/pubs/tunicates/05-appendicularia.pdf| access-date=2008-10-28| archive-url=https://web.archive.org/web/20110320223518/http://www.environment.gov.au/biodiversity/abrs/publications/electronic-books/pubs/tunicates/05-appendicularia.pdf| archive-date=20 March 2011}}</ref> 

The other two groups, the sea squirts and the salps, metamorphize into adult forms which lose the notochord, nerve cord, and post anal tail. Both are soft-bodied filter feeders with multiple gill slits. They feed on [[plankton]] which they collect in their mucus.

Sea squirts are [[Sessility (motility)|sessile]] and consist mainly of water pumps and filter-feeding apparatus.<ref name="Benton2002VertebratePalaeontologyP5" /> Most attach firmly to the sea floor, where they remain in one place for life, feeding on plankton.

The [[salp]]s float in mid-water, feeding on [[plankton]], and have a two-generation cycle in which one generation is solitary and the next forms chain-like [[Colony (biology)|colonies]].<ref>{{cite web | url=https://www.bbc.co.uk/nature/blueplanet/factfiles/jellies/salp_bg.shtml | access-date=2008-09-22 | title=Animal fact files: salp | publisher=BBC | archive-date=21 June 2013 | archive-url=https://web.archive.org/web/20130621073155/http://www.bbc.co.uk/nature/blueplanet/factfiles/jellies/salp_bg.shtml }}</ref> 

The etymology of the term Urochordata (Balfour 1881) is from the ancient Greek οὐρά (oura, "tail") + Latin chorda ("cord"), because the notochord is only found in the tail.<ref>Oxford English Dictionary, Third Edition, January 2009: Urochordata</ref> The term '''Tunicata''' (Lamarck 1816) is recognised as having precedence and is now more commonly used.<ref name="Benton2002VertebratePalaeontologyP5">{{cite book| author=Benton, M.J. | title=Vertebrate Palaeontology: Biology and Evolution| publisher=Blackwell Publishing | date=14 April 2000 | isbn=978-0-632-05614-9 | page=5| url=https://books.google.com/books?id=PQuKO7xqjNQC&q=vertebrate}}</ref>

{{multiple image
 | align = center
 | caption_align = center
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 | width     = 320
 | header    = Comparison of two<!--only 2 species shown--> invertebrate chordates
 | image1    = Comparison of Three Invertebrate Chordates.svg 
 | alt1      = 
 | caption1  = A. Lancelet, B. Larval tunicate, C. Adult tunicate<br /><small>--------------------------------------------------------<br />1. [[Notochord]], 2. Nerve chord, 3. Buccal [[Cirrus (biology)|cirri]], 4. [[Pharynx]], 5. [[Gill slit]], 6. [[Gonad]], 7. Gut, 8. V-shaped muscles, 9. Anus, 10. Inhalant [[syphon]], 11. Exhalant syphon, 12. Heart, 13. Stomach, 14. [[Esophagus]], 15. Intestines, 16. Tail, 17. Atrium, 18. [[Tunica (biology)|Tunic]]</small>
}}