Class Myxini hagfishes Order Myxiniformes Family Myxinidae

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WFB 232 Ichthyology

Taxomony: Superclass Agnatha – jawless fishes

Class Myxini - hagfishes

Order Myxiniformes

Family Myxinidae

5 genera, ~ 40 species
Description: most primitive vertebrates: degenerate eyes, cartilaginous skeleton, no vertebrae, no lateral line, jawless, anguilliform shape

gill openings, no paired fins; vestigial caudal fin; 3 pairs of barbels around mouth

isoosmotic (body fluids at same salinity as ocean)

no larval stage (that has been found)

structurally, but not functionally, hermaphroditic
Habitat: Mostly soft bottom habitat
Distribution: marine, temperate zone, intertidal to 5,000 m, mostly 25-1,500 m depths
Ecology and life history: little known of life cycle; produce few, large eggs

scavengers on dead fish; remove flesh with toothed tongue, may slide a knot along their body to apply pressure on carcass

burrow in soft sediments; often found within fish carcasses

Additional details: Economically important, used for leather and food in Asia

Exude extremely large quantities of slime (“myxin”)

First fossil evidence: Carboniferous, ~340 – 290 MYA
References used:

Bond, C. E. 1996. Biology of Fishes, 2nd. ed. Saunders College Publishing, Fort Worth

Moyle, P. B. and J. J Cech. 2000. Fishes, an Introduction to Ichthyology. Prentice Hall

Paxton, J. R. and W. N. Eschmeyer. 1998. Encyclopedia of fishes 2nd ed. Academic Press.

Taxonomy: Superclass Agnatha - jawless fishes

Class Cephalaspidomorphi

Order Petromyzontiformes - lampreys

Families Petromyzontidae

8 genera, ~ 40 species

VT species: Ichthyomyzon – single dorsal fin (silver lamprey, brook lamprey)

Petromyzon – two dorsal fins (sea lamprey)

Lampetra – fewer circumoral teeth (brook lamprey)
Description: primitive, jawless, cartilaginous, anguilliform fishes with no scales or paired fins, one or two dorsal fins and caudal fin, gill pores or slits; vertebrae present

Larvae are a few centimeters long, lack well-developed eye; adults may reach 0.6 m

Mouth of adults is a suction disk with circumoral teeth for attachment, and a few, large, rasping teeth on a ‘tongue’

Unlike Myxini, they have two semicircular canals, lateral line system, well developed eyes in adults

Habitat: Anadromous or in streams
Distribution: N. and S. America, Australia, New Zealand, Europe
Ecology and life history: Long larval stage (ammocoetes) in freshwater streams (2-7 years), followed by short adult stage in fresh or salt water (1 month - 2 years)

Highly fecund (60,000 -300,000 eggs)

Larval forms generally detritus feeders; adults may be parasitic on fish, or non-feeding

Parasitic species undergo metamorphosis, feed in fresh or salt water as juveniles, then return to streams as adults to spawn.

Non-parasitic species are stream-resident, do not feed after metamorphosis, and spawn soon after metamorphosis

Parasitic form appears to be the ancestral type

Some Australian species are predatory rather than parasitic
Additional details: parasitic sea lamprey (Petromyzon marinus) invaded the Great Lakes, has become land-locked, and has caused major economic and ecological damage to fisheries.
References used:

Bond, C. E. 1996. Biology of Fishes, 2nd. ed. Saunders College Publishing, Fort Worth

Paxton, J. R. and W. N. Eschmeyer. 1998. Encyclopedia of fishes 2nd ed. Academic Press.

Anatomy assignment

Briefly define the following, or describe where in a fish you would find it:

e.g. hemal arch: “on ventral side of caudal vertebrae”, or “arch of bone on ventral surface of caudal vertebrae”



pelvic fins


adipose fin

hypaxial muscles






On what kind of fish would you find placoid scales?
What is the function of the zygopophysis and basapophysis?
Fill in the names of the anatomical parts indicated on the diagram below:

Suggested resources: Cailliet, G., M. Love, and A. Ebeling. 1996. Fishes: a field and laboratory manual on their structure, identification, and natural history. Waveland Press, Inc., Prospect Heights, IL

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