Vertebrate Zoology - V. M. Konstantinov 2011

Chordates
Agnatha

Agnatha are the most primitive known vertebrates. The greatest evolutionary diversity of this group is noted twice: they were widely and diversely represented in the Silurian–Devonian periods, and later spread during the Anthropogene, including the present day. Their characteristic features are as follows: absence of jaws and paired appendages, a suctorial Mouth, an unpaired olfactory capsule with a single nostril, two semicircular canals in the Inner ear (in lampreys) or one (in hagfishes), and gill lamellae of endodermal origin.

Historically, agnathans were marine inhabitants. Today, their representatives live in both marine and freshwater environments.

The superclass Agnatha comprises two classes: Ostracoderms (Ostracodermii), which became extinct In the second half of the Devonian, and modern Cyclostomes (Cyclostomata).



Last update: 13/08/2026

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