Subphylum Vertebrata




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Subphylum Vertebrata
Members of the Subphylum Vertebrata differ from the urochordates and cephalochordates in having the notochord replaced by a vertebral column composed of bone and/or cartilage. The

vertebral column, along with the cranium, limb girdles, and limbs, make up the endoskeleton. This internal skeleton is an adaptation for efficient locomotion, as was the notochord. As you work through the vertebrate classes, enter the distinguishing characteristics of each in the results section table.


1. Class Agnatha. Agnathans are primitive fishes with a cartilaginous skeleton and an eel-like body. They lack a jaw as well as the scales and paired fins we usually associate with fish.

Contemporary species are scavengers or parasites (lampreys attach to the outer surface of a fish with their sucker-like mouth). Rasping teeth (arranged in a whorl) cut into the host. The lamprey then sucks blood from the wound (a fish hickey?). The injured fish usually dies from blood loss or infection. Although partially under control, the marine lamprey (Petromyzon marinus) has had a devastating effect on the fishing industry in the Great Lakes region.


Examine the preserved lamprey on demonstration. Note the single median nostril at the anterior end (between the eyes) and the seven pairs of gill apertures (making it look somewhat like an old Buick). Examine the oral disc and arrangement of the teeth. Compare the lamprey's fin arrangement and smooth, scaleless skin with that of other fish on display. If available, examine cross- and longitudinal sections of a lamprey. Note the absence of a complete internal skeleton (fragments of vertebrae and a gill basket are just about all of what remains) and the simple digestive system (with no stomach; why?). Your instructor may also have hagfish on display. They are known to fishermen as "slime eels" and have abundant mucus glands. While the lamprey may be either marine or freshwater, hagfish are exclusively marine. Unlike the lamprey, they are scavengers and are never parasitic. A hagfish's eyes are degenerate and its mouth is surrounded by eight tentacles. There may be five to 15 pairs of gill apertures, depending on the species.
While we have relied on a simple classification of vertebrates, more advanced

textbooks divide fish into two broad taxa: Superclass Agnatha (jawless fishes) and



Superclass Gnathostomata (jawed fishes). Under this arrangement, lampreys are in the

Class Petromyzontes while hagfish belong to Class Myxini. The Superclass

Gnathostomata is divided into two classes: Chondrichthyes (cartilaginous fish) and Osteichthyes (bony fish).


2. Class Agnatha- Ammocoete larva. Obtain a whole mount of an ammocoetes larva and

examine its structure (Fig 6.4). Identify the primary chordate characteristics (dorsal nerve

cord, notochord, postanal tail and pharyngeal gill slits). Follow with an examination of the

digestive structures.


3. Class Chondrichthyes. Sharks, skates, rays, and chimaeras are all members of the Class

Chondrichthyes. Their endoskeleton is entirely cartilaginous (Chondros = "cartilage"; "icthys" = "fish") and most are predaceous (as exemplified by the great white shark (Carcharodon), the principle character in the "Jaws" movie serials). Examine the display material. Note the unusual orientation of the fins as compared to the more familiar bony fish. Note that the gills are not covered (five to seven gill slits will be exposed). If the display shark can be removed from its container, run your finger over the skin.


4. Class Osteichthyes. The bony fish (Osteon = "bone"; "icthys" = "fish") are the most diverse and numerous of all vertebrates. They are widely distributed and inhabit both freshwater and marine environments (some fish can even make short sojourns over land). Unlike the cartilaginous fish, the skeleton is composed mainly of bone and the gills are covered with a flap (the operculum). Many species also have a swim bladder.
5. Class Amphibia. Amphibians include frogs, toads, salamanders, newts, and the legless caecilians. Ancestors of today's amphibians were the first tetrapod chordates to venture onto land (during the Devonian- about 350 million years ago). Despite all these years of practice with a terrestrial lifestyle, they have not completely cut their ties with water and most stay near their home ponds or streams. Limitations in their respiration and reproduction are two physiological barriers that keep most amphibians from a totally terrestrial lifestyle. Lungs, if present, are not terribly efficient so their breathing is augmented by cutaneous respiration

(absorbing oxygen through their thin, moist skin). In addition, most amphibians must

return to the water to mate and lay their eggs (which are surrounded by a soft gelatinous

material rather than hard shell). Examine the exhibit demonstrating the life cycle of a frog

(or toad) and the preserved or living amphibians on display.
6. Class Reptilia. Living members of the Class Reptilia include turtles, lizards, snakes, and

crocodilians. Ancestors to these animals were the first to completely break their ties with the

water and move to a totally terrestrial existence. Two adaptations made this possible: scaly skin and a shelled egg (both help to avoid drying). Examine the demonstration material and compare the structure of a reptilian egg to that of an amphibian.
7. Class Aves. Birds have been incredibly successful (among the chordates, they are

outnumbered only by the bony fish). The main characteristic that distinguishes them from other vertebrates is the modification of the forelimbs into feathered wings. Examine the living and preserved specimens on display to re-familiarize yourself with these lovely beasts.


8. Class Mammalia- Lions and tigers and bears. Mammals differ from other vertebrates in having hair and mammary glands. Hair grows from follicles whose base is in the lower dermal layer of the skin. Cells divide at the base of the follicle and push the hair to the surface. As the cells are pushed from the follicle, they die and are filled with a protein called keratin. The structure of the hair can be variously modified according to the needs of the animal. The surface, for example, may be scaled so that adjacent hairs clump together or the hair may be hollow (for insulation). Pigments deposited in the hair may be used for camouflage, communication, or as warning coloration (as in the skunk). Examine the preserved animals, pelts, and your lab partner to review the major characteristics of this class.

Phylum Chordata, Subphylum Vertebrata. Fill in the following table by summarizing the characteristics of each vertebrate class. Use your own observations, class notes, and text.

Vertebrate Class





Agnatha





Chondrichthyes





Osteichthyes





Amphibia





Reptilia





Aves





Mammalia






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