1. Lecture 2: Superclass Agnatha
The Jawless Fishes
Chapter 24 pp

2. I. Classification A. Living Classes 1. Myxini 2. Petromyzontida
(Hagfish) ~70 species
2. Petromyzontida
(Lamprey) ~30 species

3. B. General Characteristics
Body structure
Rounded, eel like body
Pore-like gill openings
No paired fins
No jaws
No scales
No internal ossification (bones)

4. C. Class Characteristics
1. Class Myxini (Hagfish)
Gr. myxa=slime
-Marine
-Blind, but keen sense of smell/touch
-Scavengers/predators on annelids, mollusks, crustaceans, & dead or dying fish
-Secrete milky slime when threatened
-Reproductive biology still a mystery

5. 2. Class Petromyzontida (Lamprey)
Gr. petros, stone + myzon, sucking
-Marine & freshwater
-Sucker-like oral disc/tongue with keratinized teeth
-Use mouth to grasp stone to hold position in current
-Can be up to 1 meter long
-Non-parasitic forms: do not eat after emerging as adults
-Parasitic forms: attach to prey and suck out fluids

6. II. Body Systems Skeletal/Muscular 1. Fibro-gelatinous notochord
-exists throughout lifecycle
-provides attachment for “W” shaped, serially arranged muscles (myotomes)
-muscles contract to produce S-shaped eel-like movements
2. Incomplete cartilaginous skeleton
-in head, around gills & notochord

7. II. Body Systems B. Respiratory/Circulatory 1. Gills
-5-16 pairs, variable number of openings (hagfish)
-7 pairs, each with external opening (lamprey)

8. II. Body Systems B. Respiratory/Circulatory 2. Heart
-1 heart with atrium (blood holder) and ventricle (blood pumper)
-aortic arches around gills
-accessory hearts in caudal end (hagfish)
-cold-blooded (ecto-thermic)

9. II. Body Systems C. Nervous 1. Dorsal nerve cord
2. Differentiated brain – cerebellum present in lamprey; not in hagfish
3. Pineal gland (on brain)-senses light
4. Other sense organs for taste, smell, and hearing
5. Eyes well developed in adults

10. II. Body Systems D. Digestive 1. System
-Mouth, pharynx, esophagus, intestine (liver), rectum, anus
-No stomach

11. II. Body Systems D. Digestive 2. Feeding
-described above in slides 4 & 5
-Major pests in the great lakes in 1950’s & 1960’s
-Lampreys parasites of commercial fish
-Hagfish predators of fish in nets
-Various monitoring efforts in place

12. II. Body Systems D. Digestive 3. Specialization -Mouth Parts
Rasping tongue to grind off pieces of flesh
Sucker-like mouths for easy attachment
-Flexibility
Knot tying to create more pressure against prey

13. II. Body Systems E. Excretory/Water Balance
-primitive opisthonephridic kidneys run length of body for regulating water balance
-pump in and out water
(osmosis) and ions to regulate water balance

14. II. Body Systems F. Reproduction Basics
1. Hagfish
-separate sexes (dioecious)
-both ovaries/testes; one non-functional)
-external fertilization
-large yolky egg
-no larval stage

15. II. Body Systems F. Reproduction Basics
2. Lamprey
a. Facts
-separate sexes (dioecious)
-single gonad without duct
-external fertilization
-long larval stage:
ammocoete

16. II. Body Systems F. Reproduction Basics
b. Lamprey Life Cycle
Spawn in fresh water streams
Eggs fertilized externally
Eggs hatch in 2 weeks
Larvae drift down stream
and bury in fine sand
Larvae filter food out of the
water for 3 – 7 more years
Rapid metamorphosis to adult
Adults only live ~ 1 year

17. III. Fun Facts Hagfish in store market & later stir-fry (Korea)
Lamprey Pie (London) & Salad (China)

18. IV. Alien Invaders Video
atch?v=EqskoRWMXbA -
Note taking & Summary:
Write down 5 fact-filled sentences during video
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Summarize the issue and your reaction to it on right