Jawless Fish Part II

Question 1

What is a “Fish”?

Answer 1

A “Modern Fish”
- Aquatic vertebrate with gills, limbs in the form of fins, and usually with skin covered in scales of dermal origin
“Fishes”
- “All vertebrates that are not tetrapods”
- Non-monophyletic group
- >36 000 spp. (~1/2 of all vertebrate spp.!)
- Adaptations and dominant in nearly all aquatic environments:
1) Streamlined for movement through water
2) Unique lateral line system (sensitive to water currents and vibrations)
Hagfishes, lampreys, cartilaginous fishes, ray-fins, lobe-fins

Question 2

Jawless “fishes”

Answer 2

AKA “Agnatha” (“without a jaw”)
- Include extinct “Ostracoderms” and..
Cyclostomata (“round mouth”); only living groups
- Hagfishes
- Lampreys
- No: jaws, internal ossification, scales, or paired fins
- Keratin “teeth”
- Single median nostril

Question 3

Early Jawless “Fishes” -> “Ostracoderm”

Answer 3

• Bony armour: dermal plates
• Pteraspids (heterostracans)
  
  • paired nsal openings and three-layer dermal skeleton
• Myopterygians (Osteostracans; Anaspids; Cephalapids)
  
  • paired lateral fin folds, dorsal and/or anal fins

Question 4

Class Myxini: Hagfishes

Answer 4

• ~78 spp.
• 0.5 m long adults
• slime “eels”/hag
  
  • predator defense
• Only iso-osmotic living vertebrate
• Vertebral “elements” in embryo and at tail

Question 5

No Jaws - how do they eat?

Answer 5

Bottom scavengers
- Good sense of smell and touch
- 6 “tentacles” = barbels to search out food
Keratinized rasping teeth on a protrusible “tongue”
Tail-to-head knot creates pull feeding suction and removes slime

Question 6

Class Petromyzontida: Lampreys

Answer 6

• ~40 species
• similar size and shape to hagfish
• vertebral elements along body

Question 7

Lamprey feeding

Answer 7

• Suction to the body of fishes with round mouth at the base of oral hood (funnel)
• protrusible “tongue”
• Anti-coagulant
• use oral discs to hold in onto rocks too

Question 8

Lamprey life-cycle

Answer 8

Spawn upstream in FW
Marine forms are anadromous
- leave the sea as adults to spawn upstream
- spawn in winter or spring in North America
Ammocoete larva
- Non-parasitic forms don’t feed after emerging as adults
- Adults die after spawning

Question 9

Ectoparasitic and a Nuisance

Answer 9

Great lakes in Ontario (1920s)
- Reduced lake trout, turbot, lake whitefish populations
Chemical and mechanical means to get rid of invasions?
- successful - 90% decline (DFO)