Lecture 5 - Jawless Fish Outline

Fish

One species (1 or more individuals)

Fishes

more than one species

Myxiniformes Diagnosis

• Simple cartilaginous skeleton

• jaws and paired fins absent

• dorsal fin absent

• single semi-circular canal in inner ear

• rudimentary eyes lacking musculature

• 1-16 pairs of external gill apertures

• lateral line system not developed

Hagfish

All marine, deep sea

Pest in gill net or long-line fisheries

Important as earthworms of the deep (recycle nutrients and turn decomposing carcasses into hagfish biomass

Hagfish Feeding

Greatly reduced eyes but good sense of smell and touch

Large folded tongue with horny tooth plates (keratin) tears off pieces of prey with knotted body for leverage

Engulfs food in mucous membrane for digestion

Hagfish gills

ventilate gills by bring water in through nostril.

Do not use tidal ventilation

cutaneous respiration and anaerobiosis

How hagfish endure feeding related apnea

Partially open circulatory system

Hagfish circulatory system type

Hagfish immune system

Immune system with antibodies but no defined thymus, spleen, or bone marrow

Adaptive immunity evolved independently in jawless and jawed vertebrates

isosmotic

Hagfish kidneys are simple kidneys, (?) with water

Degenerate eyes

Hagfish eyes have retinal structures but no lens.

Photoreceptive receptors in head and cloacal region

Eyes secondarily lost

Hagfish Reproduction

little known

little obvious seasonality, produce few large eggs with direct development

Lamprey identification

• lack jaws, paired fins, or scales

• single nostril, horny teeth on tongue

• dorsal fin

• second semicircular canal per side

• well developed lateral line

• innervated heart and less prevalent sinuses

• functional eyes in adults

• well developed pineal gland and kidneys

7

pairs of gills in lampreys

Gall bladder and bile ducts

two organs disappear in adult lampreys

semelparous

all lamprey are (?) with indirect development, larvae (ammocoetes) filter feeders in FW for 3-7 years. Dramatic metamorphosis going 4+ months without eating.

flow-through ventilation

Lamprey ammocoetes have this type of ventilation

tidal ventilation

adult lampreys have this type of ventilation

fresh water

all lampreys spawn in (?), use oral discs for spawning. Females produce many small eggs.

Lamprey feeding

horny teeth on disc, suction made via oral fimbriae, negative pressure in mouth helps promote flow of body fluid from prey to lamprey. Aided by anticoagulants.

true

Non-parasitic lampreys are recently derived from parasitic counterparts (true/false)

false

more than half of all lamprey species feed as adults (true/false)

true

Lampreys are only vertebrates with non-trophic adult stage (true/false)

freshwater

All lamprey spawn in freshwater or saltwater?

True

Lamprey produce many, small eggs (True or False)

Paired species problem

Closely related species where filter-feeding larvae are morphologically similar or indistinguishable but adults have different feeding types.

ex. silver and northern brook lampreys