Definition of agnathas Agnathas

We found 3 definitions of agnathas from 2 different sources.

What does agnathas mean?

🔤

Noun
agnatha - superclass of eel-shaped chordates lacking jaws and pelvic fins: lampreys; hagfishes; some extinct forms
		superclass Agnatha
		class elegance in dress or behavior; "she has a lot of class"
		craniata, subphylum craniata, subphylum vertebrata, vertebrata fishes; amphibians; reptiles; birds; mammals
		agnathan, jawless fish, jawless vertebrate eel-shaped vertebrate without jaws or paired appendages including the cyclostomes and some extinct forms
		order ostracodermi, ostracodermi extinct group of armored jawless vertebrates; taxonomy is not clear
		anaspida, order anaspida extinct order of jawless vertebrates
		conodonta, conodontophorida, order conodonta, order conodontophorida extinct order of primitive vertebrates; the precise taxonomy is not clear; in some classifications considered a separate phylum

= synonym
= antonym
= related word

Agnatha ("no jaws") is a paraphyletic superclass of jawless fish in the chordate, subphylum of the vertebrates.

Characteristics.

Agnatha have existed since the Cambrian, and continue to live in modern times. There are two extant group of jawless fish, the lampreys and the hagfish, with about 100 species between them. In addition to the absence of jaws, the Agnatha are characterised by absence of paired fins, the presence notochord both in larvae and adults; and seven or more paired gill pouches. The bronchial arches supporting the gill pouches lie close to body surface. There is a light sensitive pineal eye. There is no identificable stomach. The Agnatha are ectothermic, with a cartilaginous skeleton, and the heart contains 2 chambers.

Fossil agnathans.

Many Ordovician, Silurian, and Devonian agnathans were armored with heavy bony-spiky plates. The first armored agnathans the Ostracoderms, precursors to the bony fish and hence to the tetrapods (including human beings), are known from the middle Ordovician, and by the Late Silurian the agnathans had reached the high point of their evolution. Agnathans declined in the Devonian and never recovered.

🔤

agnathas in sign language