1. Chapter 12
Marine Fishes

2. Protochordates and Jawless Fishes
Section 12.1
Protochordates and Jawless Fishes

3. Objectives
List the distinguishing features of the protochordates and the jawless fishes
Explain the importance of studying protochordates
Discuss the differences between the protochordates and jawless fish.

4. Classification Phylum Chordata (Chordates)
Hollow dorsal nerve cord
Notochord (flexible, rodlike, supports spinal cord)
Pharyngeal gill slits
Protochordates “first chordates”
Subphylum Vertebrata (Vertebrates)
Skeleton
Backbone
Skull
Brain

5. protochordates
Agnatha
vertebrates

6. An evolutionary Connection
Vertebrates include fish, amphibians, reptiles, birds, and mammals.
Vertebrates differ from protochordates:
Both have a notochord, but in vertebrate embryos it develops into a backbone
The ancestors of protochordates are the link between invertebrate animals and vertebrates!

7. Protochordates Sea squirts (tunicates)
Covered by a clear tough membrane
Incurrent/excurrent siphon
Hermaphrodite with no self fertilization
External fertilization
Larva is fishlike, with dorsal nerve cord, a notochord, and gill slits
Adult lives attached to substrate and these structures dissappear

8. Tunicate Larva

9. Protochordates Lancelets (Amphioxus) Tiny, transparent, fishlike
Lives buried in sand, filter feeds plankton
Adult retains dorsal nerve cord, notochord, and gill slits
Separate sexes
External fertilization and development

10. Lancelet

11. Jawless Fishes Superclass Agnatha “without jaws”
The most primitive of the vertebrates
Lack jaws and a true backbone
Adults retain the larval notochord
Two extant groups
Hagfish
Lamprey
Lamprey
Hagfish

12. Jawless Fish Sea Lamprey (Petromyzon marinus) parasitic
Lives in estuaries from Maine to Florida
Uses sucking disk on its mouth to attach to living trout and other host fish
Uses teeth and rasping tongue to make a hole, then sucks out blood and tissue

13. Sea Lamprey Damage

14. Jawless Fish Pacific and Atlantic Hagfish
Use sharp teeth in their rounded mouth to burrow into bodies of dead or dying fish
devour prey from the inside
Secrete mucus (slime) when captured to evade predators

15. Jawless Fish

16. Cartilaginous Fishes
12.2

17. Cartilage
Cartilage is a flexible connective tissue composed of cells and proteins
Your ears, nose, and joints contain cartilage!

18. Cartilaginous Fishes Class Chondrichthyes “cartilage fishes”
Contains Sharks, Skates, and Rays

19. Characteristics First Jawed fish
Have placoid scales –tiny teeth embedded in the skin (feels like sandpaper)
ventral gill slits (breathing) with no flap
Spiracles – breathing holes behind each eye

20. Characteristics Ventral mouth Rigid fins
Pectoral fins provide lift to prevent sinking and to glide

21. Rays and Skates Highly developed pectoral fins for swimming
Many are bottom dwellers
Ventral mouth for bottom feeding

22. Rays Stingray (Dasyatis)
Lives in the sand in the Gulf of Mexico and from Carolinas to Brazil
Sharp spine on tail for defense

23. Skates Skate (Raja) No spine on tail
Found in temperate waters along the Atlantic and pacific coasts
Eat crustaceans and mollusks in subtidal zone

24. Sawfish Unusual Cartilaginous fish Virginia to Brazil, and the Gulf
Long bladelike snout full of teeth
Uses snout as weapon to stun and kill prey fish

25. Sharks!
About 350 known species

26. Structure and Behavior
Sharks are called “living fossils” because they resemble some early ancestral forms
Sharks have very sensitive sensory receptors

27. Lateral line Organ A faint line along each side of a sharks body
Picks up sound vibrations over long distances

28. Sense of Smell
Can detect small amounts of blood over half a kilometer away
2/3 of the sharks brain is dedicated to smelling!

29. Ampullae of Lorenzini Tiny pores in the shark’s snout (rostrum)
Sense the electric fields generated by the muscles of fish and other prey
How might this be beneficial at night?

30. Body shape and Movement
Sharks are streamlined for quickly moving through water
Accelleration accomplished by powerful muscle contractions along the sides of body
Move the caudal fin and generate thrust

31. Teeth Predatory sharks have several rows of teeth
Lost teeth are replaced by new teeth from behind
Hunneds of teeth!

32. Reproduction Internal fertilization
Male sharks have claspers between pelvic fins
Transfer sperm into females reproductive tract
Claspers

33. Gestation and Birth Vivipary Ovovivipary Ovipary
Live young develop inside mother
Ovovivipary
Eggs hatch within mother
Oophagy
Hatched young eat unhatched eggs
Ovipary
Eggs are laid and hatch externally

34. Mermaid’s Purse Egg casing produced by some sharks and skates
Black and leathery
1 or more embryos develop within (>1 year)