Jawless Fishes

Review of Chordates (fig. 7.51)Table 7.1

• dorsal hollow nerve cord

• notochord (dorsal, elastic supporting rod)

• paired pharyngeal gill slits

• post-anal tail

Chordates

• 3 sub-phyla under group Acrania (Protochordata)

1. Subphylum Urochordata (Tunicates, Sea Squirts)

2. Subphylum Cephalochordata (Lancelets)

3. Subphylum Vertebrata (Vertebrates) – cranium/brain• Chordates w/ a backbone, skull, brain, and

kidneys

Lanelet(amphioxus) & Tunicate

Phylum Chordata Subphylum Vertebrata

– class Agnatha (Lampreys)– Class Chondrichthyes (Elamobranchii)– Class Osteichthyes (Bony Fishes)– Class Amphibia– Class Reptilia– Class Aves– Class Mammalia

Jawless FishPhylum: Chordata

Sub-Phylum: Vertebrata

Class: Agnatha • There are two primary marine types of the class

Agnatha. They are Hagfish and Lampreys. • Most Primitive living fishes• Hagfish are of the order, Myxiniform. They are

related to the slimefish. They have the peculiar habit of tying themselves into knots in order to shed their slime coat and make a new one.

Classification p.156 (fig.8.1)

• Kingdom Animalia--Phylum Chordata----Subphylum Vertebrata – Class Agnatha

Hagfishes

• 20 known species

• Deep, cold waters

• 2.6 ft.

• Skin is used for leather goods

Hagfish

• feed on polychaete worms, shrimp, and dead or dying fish

• attach to fish, form a knot in the tail and pass it forward to rip off flesh.  Image © BIODIDAC.

• usually enter coelomic cavity and feed on soft parts

• many mucous glands present for antipredator defense

Lampreyshttp://itech.pjc.edu/jwooters/zoology/virtual_review/lamprey.htm

• Lampreys are of the order, Petromyzontiform. They are suckers and attach themselves to fish in order to parasitize off them.

• Found in Freshwater• 30 species

Sea Lamprey Life Cycle• A. Sea lampreys go through an extended larval phase before metamorphosing into the

bloodsucking parasitic phase. Each summer and fall there is one group of parasitic sea lampreys actively feeding in the Great Lakes.

B. The next spring, that group leaves the lake and migrates into tributary streams where they must build nests in clean gravel with flowing water.

C. Each female spawns an average of 60 to 70 thousand eggs.

D. After hatch, the larvae drift downstream to areas with slower currents and sand/silt bottoms. There, they establish permanent burrows and enter a larval stage varying in duration from 3 to 10-ormore years.

E. Larvae lack eyes and the oral disc. Living concealed in their burrows, they are harmless and filter microscopic material from the water for food. When they reach lengths of 120 mm or more, some individuals begin metamorphosis in mid summer.

F. During metamorphosis they develop eyes, the oral disc, and changes in their kidneys that (in their native range) would allow them to enter the salt water of the Atlantic Ocean. That fall or the following spring, they instead enter the Great Lakes to feed parasitically on fish that summer and fall, and mature and spawn the next spring—completing their life cycle. Sea lampreys only spawn once and then die after spawning.

Lamprey on a SalmonVideo

Lamprey Anatomy

D-eel-icious, if you appreciate an earthiness

• So what does lamprey taste like? "I would have to say it tastes like lamprey," says Chef Bob Bennett, "because it does not have a flavor that you can associate with anything else."

Critical Thinking???Discuss this with your partner(s)

• Hagfishes have tiny eyes buried beneath the skin and lampreys have large, exposed eyes. Explain how each type of eye is an adaptation for feeding style.

Critical Thinking???Discuss this with your partner(s)

• How & why would the respiration process differ from a lamprey to a bony fish?

Interpret This Graph