Comparative Vertebrae Anatomy Class Agnatha

Which class developed primitive jaws and paired fins, and was covered with a well-developed bony armor?

What is a key characteristic that distinguishes Agnatha from other classes mentioned in the text?

How do sharks reproduce according to the information provided?

What distinguishes Myxinoidea (Hagfishes) from other Cyclostomes mentioned?

Which class has sharks as members and is characterized by a cartilaginous skeleton?

What feature is specific to male sharks for fertilization according to the text?

Which class of vertebrates has some members that reproduce through internal fertilization resulting in live young?

What distinguishes Class Osteichthyes from Class Chondrichthyes regarding fertilization?

What is a distinguishing feature of Elasmobranchii (Selachii) under Class Chondrichthyes?

Which class of vertebrates in the text lays eggs without a protective shell?

What is a common characteristic of Class Amphibia mentioned in the text?

In which class of vertebrates are some members known to have dermal bones derived from ancestral bony plates?

Agnatha

Most primitive and widely distributed vertebrates
Characterized by the absence of jaws and jawless mouth
Mouth is round and armed with a rasping, tongue-like structure
Lacked true paired fins
Lateral projections used for balancing and steering

Orders of Agnatha

Ostracoderms
- Extinct
- Armored with bony plates and some had internal skeletons of bone
Cyclostomes
- Myxinoidea (Hagfishes)
  - Marine and internal parasites on fish
  - Lack sucking disk and vertebrae
  - 6-14 gill slits

Placodermi

Evolved from Ostracoderms
Extinct
Characterized by the development of primitive jaws and paired fins
Body covered with a well-developed, bony armor of scales or large plates

Chondrichthyes

Evolved from Placoderms
Still abundant and flourishing group
Characters:
- Cartilaginous skeleton
- Well-developed jaws and paired fins
- Two-chambered heart
- Scales are placoid
- Young are born alive or eggs are encased in an elaborate, horny shell
- Eggs must be fertilized within the body of the female
Male Sharks:
- Claspers transmit sperms to the cloaca of the female

Orders of Chondrichthyes

Elasmobranchii (Selachii)
- Typical sharks (Suborder Squali)
- Skates and rays (Suborder Squali)
- Lacked operculum, exposing the gills

Osteichthyes

Class of bony fishes
Characters:
- Skeletons contain bone
- Some skull bones are dermal bones, derived from ancestral fish bony plates
- Majority have external fertilization
- Some have internal fertilization (young are born alive)

Amphibia

First vertebrates to move out on land
First of tetrapod classes (paired limbs with digits instead of fins)
Characters:
- Soft, glandular skins, without scales
- Methods of respiration: Lungs, Gills of the larvae
- Three-chambered heart
- Skin is important in respiration
- Lacks shell among their eggs, laid in water

Test your knowledge on the most primitive and widely distributed vertebrates, Agnatha, characterized by their jawless mouth, lack of true paired fins, and unique lateral projections. Learn about the orders within Agnatha including Ostracoderms and Cyclostomes suborders like Myxinoidea.