Zoology lecture phylum Chordata

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Phylum Chordata

Major Characteristics of Phylum Chordata

1. Bilateral symmetry; segmented body; three germ layers; well-developed coelom.

2. Notochord (a nerve cord) present at some stage in life cycle.

3. Pharyngeal gill slits present at some stage in life cycle.

4. Postanal tail, usually projecting beyond the anus at some stage but may or may not persist.

5. Segmented muscles in an unsegmented trunk.

6. Ventral heart, with dorsal and ventral blood vessels; closed blood system.

7. Complete digestive system.

8. A cartilaginous or bony endoskeleton present in the majority of members

Biological Contributions

1. The endoskeleton of the vertebrates permits

2. The perforated pharynx of

3. The adoption of a predatory habit by the early vertebrates and

4. The paired appendages that appeared in the aquatic vertebrates were

Four Chordate Hallmarks

  • When taken together, set chordates apart from all other phyla are:


  • It is the first part of the endoskeleton to appear in an embryo; It is an axis for muscle attachment, and because it can bend without shortening, it permits movements of the body.







Characteristics of Jawless Fishes

1) Slender, eel-like body

2) Median fins but no paired appendages

3) Fibrous and cartilaginous skeleton; notochord; no vertebrae

4) Biting mouth with two rows of eversible teeth in hagfishes;

suckerlike oral disc with well-developed teeth in lampreys

5) Heart with one atrium and one ventricle. Hagfish with three accessory hearts; aortic arches in gill region

6) Five to 16 pairs of gills and a single pair of gill apertures in hagfish; 7 pairs in lampreys.

7) Dorsal nerve cord with differentiated brain; 8 to 10 pairs of cranial nerves

8) Digestive systems without stomach; intestine with spiral valve and cilia in lampreys; both lacking in intestine of hagfishes

9) Sense organs of taste, smell, hearing; eyes poorly developed in hagfishes but

moderately well developed in lampreys

10) External fertilization

  • Both ovaries and testes present in an individual but gonads of only one sex functional and no larval stage in hagfishes; separate sexes and long larval stage with radical metamorphosis in lampreys

Superclass Agnatha: Jawless Fishes

  • The __________________________________are represented by approximately _____________________________ almost equally divided between two classes:

  • 1)

  • 2)

  • Members of both groups lack:

  • 1)

  • 2)

  • 3)

  • 4)

  • In other respects, however, the two groups are morphologically very different.

Hagfishes: Class Myxini

  • The hagfishes are an entirely marine group that ___________________________


  • There are only ___________species of hagfishes, of which the best known in North America are the Atlantic hagfish and the Pacific hagfish

  • Although ___________________________, the hagfish is quickly attracted to food, especially dead or dying fish, by its keenly developed senses of smell and touch.

  • Hagfishes have several other anatomical and physiological peculiarities,


  • 1) __________________________________________served by three accessory hearts in addition to the main heart positioned behind the gills.

  • 2)

Lampreys: Class Cephalaspidomorphi

  • Of the ___________________________________species of lampreys distributed around the world, by far the best known to North Americans is the destructive marine lamprey of the Great Lakes

  • There are ______________of lampreys in North America of which about half are parasitic; the rest are species that never feed after metamorphosis and die soon after spawning.


  • ________________________________ either migrate to the sea, if marine, or remain in fresh water, where they attach themselves by their sucker-like mouth to fish and with their sharp horny teeth rasp through flesh and suck the body fluids.

  • Within a few months and after spawning, they die.


Cartilaginous Fishes: Class Chondrichthyes

Characteristics of the Sharks and Rays

1. Body fusiform (except rays) with a heterocercal (Upper lobe is larger than the lower lobe) caudal (tail) fin

2. Mouth ventral; two olfactory sacs that do not connect to the mouth cavity; jaws present

3. Skin with placoid scales (sandpapery) and mucous glands, teeth of modified placoid scales

4. Endoskeleton entirely cartilaginous

5. Digestive system with a J-shaped stomach and intestine with spiral valve

6. Circulatory system of several pairs of aortic arches; two-chambered heart

7. Respiration by means of five to seven pairs of gills with separate and exposed gill slits, no operculum

8. No swim bladder or lung

9. Brain of two olfactory lobes, two cerebral hemispheres, two optic lobes; 10 pairs of cranial nerves; senses of smell, vibration reception (lateral line system), and electroreception well developed

10. Separate sexes; direct development; internal fertilization

Cartilaginous Fishes: Class Chondrichthyes

  • _____________________________: Reproduction in which eggs are released by the female, ______________________________________


  • ____________________________________: Reproduction in which eggs develop within

  • __________________________________: Reproduction in which eggs develop within the female body,

  • There are more than _________________________________in the class Chondrichthyes, an ancient, compact, and highly developed group.

  • One of their distinctive features is their _________________________________.

__________________________________– a curious feature, since the Chondrichthyes are derived from ancestors having well-developed bone.

Sharks and Rays: Subclass Elasmobranchii

  • Sharks, which make about _________________________________________are typically predaceous fishes.

  • Sharks track their prey using their _____________________________and large olfactory organs, since their vision is not well developed.

  • The __________________________________rarely exceed 1 m.

  • More than half of _______________________________________________, specialized for a bottom-feeding life-style.

  • Unlike sharks, which swim with thrusts of the tail,

  • The ______________________________________________________________, in which the vertebral column turns upward and extends into the dorsal lobe of the tail, provides lift and thrust as it sweeps to and fro in the water, and the broad head and flat pectoral fins act as planes to provide head lift.

  • Sharks are well equipped for their _________________________________.

  • The tough leathery skin is covered with ________________________________ that are modified anteriorly to form replaceable rows of teeth in both jaws.

  • Sharks have___________________________________________used to guide them to food.

  • ________________________________________________________________, but a well-developed lateral line system is used for detecting and locating objects and moving animals (predators, prey, and social partners).

  • It is composed of a

  • Inside are ___________________________________________________ that are extremely sensitive to vibrations and currents in the water.

  • The receptors, _______________________________________________, are located on the shark's head.

  • Rays are distinguished by their __________________________________________ and the much-enlarged pectoral fins that behave as wings in swimming.

  • The gill openings are on ______________________________, and the ___________________________________________ are unusually large.

  • The teeth are adapted for crushing the prey –

  • In the stingrays, __________________________________________have disappeared, and the tail is slender and whiplike.

  • The stingray tail is armed with one or more _____________________________


  • Electric rays have certain ____________________________________ modified into powerful electric organs, which can give severe shocks to stun their prey

Class Osteichthes (Bony fishes)

If you need a refresher, read pages 510-523

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