agnathan

Introduction & Top Questions
General features
Form and function
Evolution and classification
- Evolution
- Annotated classification
- Critical appraisal

References & Edit History Quick Facts & Related Topics

Images

Illustration of a Petromyzon, a jawless fish with an elongated, eel-like body and a rounded mouth, shown with a scale bar indicating 10 centimeters and 4 inches for size reference.

Illustration of a Myxine, or hagfish, showing its long, slender, eel-like body with smooth skin. A scale bar below indicates length in centimeters and inches for size reference.

A branching diagram shows the evolutionary relationships among fossil and modern jawless fishes (Agnatha), with illustrations of Petromyzon, Myxine, Pharyngolepis, Pteraspis, Hemicyclaspis, and Drepanaspis along a timeline from the Ordovician period to the present.

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Related Questions

Did the earliest vertebrates evolve in freshwater or marine habitats?
How are agnathans different from jawed vertebrates?
How could freshwater streamflow have influenced the evolution of dermal armour in early vertebrates?
How deep can hagfishes live in the ocean?
How did early agnathans probably feed on tiny organisms?
How did the gill apparatus of early agnathans help with feeding?
How do ammocoete larvae feed while buried in stream silt?
How do brook lampreys differ from parasitic lampreys?
How do hagfishes defend themselves with slime?
How do hagfishes find food?
How do hagfishes use their horny tooth plates to feed?
How do lampreys attach to other fishes?
How do the gill openings of Myxinidae differ from those of Eptatretinae hagfishes?
How do the pouchlike gills of agnathans differ from the gills of jawed fishes?
How does a lamprey rasp through the tissues of its prey?
How does a male lamprey prepare a nest for spawning?
How does the endostyle of a lamprey larva change during metamorphosis?
How many gill pairs do lampreys have?
How might a notochord have supported the earliest ancestors of jawless fishes?
How old is the fossil lamprey discovered in Illinois?
What changes occur during lamprey metamorphosis?
What do hagfishes eat?
What happens to many lampreys after they spawn?
When was the first fossil lamprey with a modern body structure reported?
Where do lampreys lay their eggs?
Where were the earliest Heterostraci fossils discovered?
Which body structures do agnathans lack compared with gnathostomes?
Which extinct agnathan groups had bony head shields?
Which features of ancient agnathans were usually preserved as fossils?
Which features suggest that some Osteostraci lived on the bottom?
Which fishes were harmed by sea lampreys in the Great Lakes?
Why can hagfishes be pests for commercial fisheries?
Why did armoured jawless vertebrates probably disappear after the Devonian Period?
Why do many adult lampreys migrate from the sea into freshwater streams?
Why were bone and cartilage important innovations in vertebrate evolution?
How do lampreys reproduce?
What distinguishes agnathans from other craniates?
How do hagfishes feed?
How do reptiles contribute to the ecosystem?
How do reptiles reproduce?
What is the largest living reptile?
How are mammals distinct from other animals?
Why is the platypus a mammal?
What are the unique characteristics of birds?
How do birds adapt to flight and flightlessness?

Science Birds, Reptiles & Other Vertebrates Fish

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lamprey Lamprey (*Lampetra*) on rainbow trout.

agnathan

vertebrate

Also known as: Agnatha, jawless fish

Written by

Ronald Strahan

Honorary Historian, Australian Museum, Sydney. Director, Taronga Zoological Park, Sydney, 1967–74. Coauthor of The Biology of Myxine.

Ronald StrahanAll

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Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

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History

agnathan, (superclass Agnatha), any of approximately 160 living species that make up the group of primitive jawless fishes that includes the lampreys (order Petromyzoniformes) and hagfishes (order Myxiniformes), as well as several extinct groups. Hagfishes are minor pests of commercial food fisheries of the North Atlantic, but lampreys, because of their parasitic habit, have been a serious pest of food fisheries in the Great Lakes in North America, where they have reduced the numbers of...

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