Käklösa fiskar

Käklösa fiskar
Stratigrafisk utbredning: Tidig kambrium - Nutid
Systematik
DomänEukaryoter
Eukaryota
RikeDjur
Animalia
StamRyggsträngsdjur
Chordata
UnderstamRyggradsdjur
Vertebrata
ÖverklassKäklösa fiskar
Agnatha
Vetenskapligt namn
§ Agnatha
Klasser
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Käklösa fiskar (Agnatha) är en grupp fiskar som tillhör understammen ryggradsdjur. Det är en grupp som dök upp på jorden för drygt 500 miljoner år sedan, under Kambrium. De brukar kallas pansarrundmunnar och tillhör de käklösa fiskarna. Under Devonperioden för ungefär 350 miljoner år sedan konkurrerades de flesta arterna av käklösa fiskar ut. Nejonögon och pirålar är nu levande arter av käklösa fiskar. Totalt finns det endast ett femtiotal arter på jorden idag.[1]

Egenskaper

De viktigaste kännetecknen för Agnatha, genom vilka de avviker från Gnathostomata är att näsgången är oparig och har gemensam mynning med hypofysgången, munnen saknar verkliga käkar, gälarna är säckformiga, det inre skelettet är broskigt och att egentliga gälbågar saknas. Även extremiteter saknas, men dock finns hos en del fossila former ett främre par fenlika bihang, som dock kanske ej är homologa med fiskarnas bröstfenor.[2]

Klasser

Referenser

  1. ^ ”Käklösa fiskar (Agnata) - De första fiskarna”. http://www9.vgregion.se/vastarvet/gnm/evolution/rund1.htm. Läst 28 november 2014. 
  2. ^ Svensk Uppslagsbok, Band 1, 1947-1955. (spalt 329)
  3. ^ Sara Eliason. Solstenar och kattskallar - Gotländsk fossil- och geologiguide. sid. 112 
  4. ^ Shubin, Neil (2009). Your Inner Fish: A Journey into the 3.5 Billion Year History of the Human Body. Pantheon Books, New York. sid. 85–86. ISBN 978-0-30-727745-9 
  5. ^ William Antony S. Sarjeant, L. B. Halstead (1995) (på engelska). Vertebrate fossils and the evolution of scientific concepts: writings in tribute to Beverly Halstead. Gordon & Breach. ISBN 978-2-88124-996-9. http://books.google.com/?id=B3leE3TTeuIC&pg=PA146. Läst 28 november 2014 
  6. ^ P. C. J. Donoghue, M. P. Smith (2001). ”The anatomy of Turinia pagei (Powrie), and the phylogenetic status of the Thelodonti” (på engelska). Transactions of the Royal Society of Edinburgh: Earth Sciences 92 (1): sid. 15–37. doi:10.1017/S0263593301000025. http://www.ingentaconnect.com/content/rse/tes/2001/00000092/00000001/art00002. Läst 28 november 2014. 

Externa länkar

Katalogdata
 • AFD: AGNATHA​​​​​ • EoL: 55867450​​​​​ • ITIS: 914178​​​ • Fossilworks: 91606​ • WoRMS: 1829​​​​​​​​​​​​​​​ • Fauna Europaea: 11998​​​​​​​​​​​​​

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