12 Questions
Which class developed primitive jaws and paired fins, and was covered with a well-developed bony armor?
Placodermi
What is a key characteristic that distinguishes Agnatha from other classes mentioned in the text?
Lack of jaws
How do sharks reproduce according to the information provided?
By giving live birth
What distinguishes Myxinoidea (Hagfishes) from other Cyclostomes mentioned?
Lack of vertebrae
Which class has sharks as members and is characterized by a cartilaginous skeleton?
Chondrichthyes
What feature is specific to male sharks for fertilization according to the text?
Internal sperm transfer through claspers
Which class of vertebrates has some members that reproduce through internal fertilization resulting in live young?
Class Chondrichthyes
What distinguishes Class Osteichthyes from Class Chondrichthyes regarding fertilization?
Class Osteichthyes have external fertilization, while Chondrichthyes have internal fertilization.
What is a distinguishing feature of Elasmobranchii (Selachii) under Class Chondrichthyes?
Lacks operculum covering the gill chamber.
Which class of vertebrates in the text lays eggs without a protective shell?
Class Amphibia
What is a common characteristic of Class Amphibia mentioned in the text?
Three-chambered heart.
In which class of vertebrates are some members known to have dermal bones derived from ancestral bony plates?
Class Osteichthyes
Study Notes
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
- Myxinoidea (Hagfishes)
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.
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