Gnathosomes

Question 1

Class Myxini- hagfishes

Answer 1

*The most primitive (cartilaginous) skull
Rudimentary eyes and 1 nostrilLong bodies with 12 pairs of gills – but exhale via single openings on each side
*Multiple slime gland openings
*They have tooth-like formations made of keratin
*They don’t have jaws, vertebrae, dorsal or paired fins

Question 2

Class Petromyzontida- lampreys

Answer 2

*Cartilage skeleton (without collagen)
*Flexible sheath around the notochord. *This has cartilaginous projections that are related to vertebrae (vestigial)
*Dorsal fin
*No jaws

Question 3

Gnathostomes

Answer 3

Gnathos= jaw; stoma = mouth
Evolved from mineralized skeletal rods between the pharyngeal slits
Duplication of the Hoxgenes from 1 set to 4
Enlarged brain, with advanced smell and vision
Lateral line system

Question 4

Class Chondrichthyes

Answer 4

Chondros= cartilage; ichthyes= fishes
Traces of bone in their fins (fossil forms), scales, dental bases, vertebral surface

Question 5

Electroreception

Answer 5

Lorenzini ampullae
They are modified neuromast organs
It detects electric fields that are generated by the muscle contractions of nearby animals (bioelectric currents)\

Question 6

Skin Denticles

Answer 6

The skin is covered with placoid denticles
They reduce drag and protect the body
Diagnostic for many shark groups\

Question 7

Te e t h

Answer 7

They are modified denticles
They are arranged in many rows
Polyphyodont-They are replaced many times during the life of the animal