Jawless Fish Part II Flashcards
What is a “Fish”?
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
Jawless “fishes”
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
Early Jawless “Fishes” -> “Ostracoderm”
- 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
Class Myxini: Hagfishes
~78 spp.
- 0.5 m long adults
- slime “eels”/hag
- predator defense
- Only iso-osmotic living vertebrate
- Vertebral “elements” in embryo and at tail
No Jaws - how do they eat?
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
Class Petromyzontida: Lampreys
~40 species
- similar size and shape to hagfish
- vertebral elements along body
Lamprey feeding
- 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
Lamprey life-cycle
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
Ectoparasitic and a Nuisance
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)