University:
University of Georgia
Course:
BIOL-4245 | Ichthyology
Academic year:

2024
Views:

387

Pages:

2
Author:

Accinkiquicpqw

General Characteristics of Agnatha Intro: Agnatha (Greek, "No Jaws") is a superclass of jawless fish in the phylum Chordata, sub-phylum Vertebrata, consisting of both present (cyclostomata) and extinct (conodonts and ostracoderms) species. The group of excludes all vertebrates with jaws, known as gnathostomes. The oldest fossils of agnathans appeared in the Cambrian, and two groups still survive today, the lampreys and the hagfish. Agnathans were prominent among the early fish in the early Paleozoic. Characteristics Features of Agnatha In addition to the absence of jaws, modern agnathans are characterized by the absence of paired fins. Presence of a notochord both in larvae and adults. They are only known living animals that have a skull but not a vertebral column. Seven or more paired gill pouches. Lampreys have a light sensitive pineal eye. (homologous to the pineal gland in mammals). All living and most extinct Agnatha do not have an identifiable stomach. Alimentary canal: They have no distinct stomach, but rather a long gut, more or less homogeneous throughout its entire length. Nutrition: Lampreys feed on other fish and mammals. They rely on a row of sharp teeth to shred their food. Hagfish are “scavengers”, eating mostly “dead animals”. They also use a sharp set of teeth to break down the animals. Body covering: In modern agnathas, the body covering is “skin”, with neither dermal nor epidermal scales. The skin of “hagfish” has copious “slime glands”. Appendages: Almost all agnathas, including all extant agnathas, have no paired appendages, although most have a dorsal and a caudal fin. Reproduction: Fertilization in lampreys is external. There is no known parental care. It is believed that hagfish only have 30 eggs over a lifetime. Agnatha are ectothermic or cold blooded, with a cartilaginous skeleton, and the heart contains 2 chamber.

Agnatha Characteristics

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