Download The Chordates - Paxon Biology

The Chordates
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Phylum: Chordata
- Chordates are distinguished from all invertebrates by the presence of 4 anatomical
structures.
- The structures can be present at any point of the animal’s life.
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Notochord
- A flexible, longitudinal rod located between the digestive tube and the nerve
cord.
- Provides skeletal support.
- In invertebrates, it persists throughout the life of the animal.
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- In vertebrates, a supportive skeleton develops and the notochord degenerates.
Dorsal, Hollow Nerve Cord
- The nerve cord develops into the central nervous system (brain & spinal cord).
- Invertebrates have a nerve cord, but it is solid and usually ventrally located.
- The nerve cord is ectoderm in origin.
Pharyngeal Gill Slits
- Present in all embryos.
- Persist in aquatic animals for respiration and or filter feeding.
Postanal Tail
- Present in all embryos.
- Turns into a tail for many vertebrates.
- Some vertebrates reabsorb the tail as development continues (frogs, humans).
- Figure 34.2 Chordate characteristics
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Subphylum: Urochordata (tunicates)
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Subphylum: Cephalochordata (lancelets)
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Subphylum: Vertebrata (the vertebrates)
All have a closed circulatory system.
The neural crest forms some bones and the cranium.
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It is a collection of embryonic cells.
Class: Agnatha
- Jawless fish.
- All are extinct except for lampreys and hagfishes.
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Class: Placodermi
- The placoderms.
- All are extinct.
- Had thick, tough plates on skin.
- Were the first jawed fishes.
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Class: Chondrichthyes
- Sharks, skates, chimaeras and rays.
- All have cartilage instead of bone.
- 750 extant species
- Well developed lateral line system.
- They show all 3 types of development/birth:
- Oviparous: lay eggs that hatch outside of the mother’s body.
- Ovoviviparous: fertilized eggs develop inside the body. Nutrition comes
from yolk. Eggs hatch inside mother and “live birth” to a well-developed
young occurs.
- Viviparous: true “live birth”. Young is nourished by a placenta-like
structure.
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Class: Osteichthyes
- Bony fish.
- About 33,000 species.
- Have a swim bladder (filled with air).
- Have a 2 chambered heart.
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Class: Amphibia
- Includes frogs, salamanders.
- 4,000 species.
- Still tied to the water for reproduction.
- Most require a moist skin surface for respiration.
- 3 chambered heart (2 atria, 1 ventricle)
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Class Reptilia:
- Snakes, lizards, turtles, crocodiles.
- Have become less dependent of water for reproduction.
- The movement on land is due to the evolution of the amniotic egg.
- Scales made of keratin prevents desiccation.
- 7,000 species.
- All are ectotherms (“cold blooded”).
- All have a 3 chambered heart except for crocodiles (4 chambered).
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Class: Aves
- The birds.
- 8,500 species
- Share reptile characteristics of scales on legs and reproduction with an
amniotic egg.
- 4 chambered heart with “double respiration”
- Anatomy is modified for flight:
- Hollow bones
- Lightweight feathers
- Only 1 ovary
- No copulatory organ in males.
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Class: Mammalia
- The mammals.
- All have 4-chambered heart.
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Have fur (hair), most give live birth and young develop in a placenta. There
are 3 major groups:
1. Monotremes : egg layers
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2. Marsupials: pouched
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3. Eutherians: placentals
Some common orders:
- Monotremata
(hedgehog)
- Marsupialia
(kangaroos, koalas)
- Carnivora
(dogs, seals, weasels, raccoons, walrus, cats)
- Cetacea
(dolphins, whales)
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Artiodactyla
Perissodactyla
Chiroptera
Lagomorpha
Primates
Rodentia
Proboscidea
Sirenia
(sheep, giraffes, cows, pigs, [even # of toes])
(rhinos, horses, zebras, [odd # of toes])
(bats)
(rabbits)
(monkeys, humans)
(capybara, beavers, prairie dogs)
(elephant)
(manatee)