Lecture 2 Superclass Agnatha The Jawless Fishes Chapter

Lecture 2: Superclass Agnatha The Jawless Fishes Chapter 24 pp. 520 -525

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

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

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

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

II. Body Systems A. 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

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

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)

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

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

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

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

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

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

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

II. Body Systems F. Reproduction Basics b. Lamprey Life Cycle Ø Ø Ø Ø 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

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

IV. Alien Invaders Video http: //www. youtube. com/w atch? v=Eqsko. RWMXb. A - Note taking & Summary: Write down 5 fact-filled sentences during video 1. ________________________ __ 2. ________________________ _ 3. ________________________ _ 4. ________________________ _ 5. _________________________ Summarize the issue and your reaction to it on right