Agnatha
Agnatha
Agnatha (pronunciation: /æɡˈneɪθə/) is a superclass of jawless fish in the phylum Chordata. The term is derived from the Greek words 'a' meaning 'without' and 'gnathos' meaning 'jaw'.
Etymology
The term Agnatha is of Greek origin. It is a combination of two words: 'a' which means 'without' and 'gnathos' which means 'jaw'. This name is given due to the absence of a proper jaw in these species.
Classification
Agnatha is a superclass that includes two extant groups, namely the Lampreys and the Hagfish. These are the only known living organisms that come under this superclass. They are characterized by their elongated bodies, similar to eels, and the absence of paired fins.
Characteristics
Agnathans are characterized by the absence of a jaw, paired fins, and scales. They have a cartilaginous skeleton and a notochord that persists throughout their life. The heart is two-chambered, with one atrium and one ventricle. The skin of agnathans is smooth and scaleless.
Evolution
The Agnatha group is considered the earliest group of vertebrates, and they have undergone little evolutionary change. The first agnathans appeared in the Cambrian period, and the group includes the extinct Conodonts and Ostracoderms.
Related Terms
- Chordata: The phylum to which Agnatha belongs.
- Lampreys: An extant group of jawless fish that falls under the Agnatha superclass.
- Hagfish: Another extant group of jawless fish that falls under the Agnatha superclass.
- Cambrian: The geological period when the first Agnathans appeared.
- Conodonts and Ostracoderms: Extinct groups of Agnathans.
External links
- Medical encyclopedia article on Agnatha
- Wikipedia's article - Agnatha
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