UNIT 8

Chapter 32: Introduction to Animal Evolution

Chapter 33: Invertebrates

Chapter 34: Vertebrate Evolution & Diversity

Organisms that belong in Kingdom Animalia must satisfy five requirements.

1. Animals are multicellular, eukaryotic and heterotrophic

- Animals ingest preformed organic materials

Features of Animals

2. Animal cells lack cell walls

- Multicellular bodies held together by extracellular proteins, especially collagen

3. Animals have two unique tissue types: nervous and muscle

- Nervous tissue involved with impulse (action potential) conduction

- Muscle tissue for movement

4. Most animals reproduce sexually and the diploid stage is dominant

- In most species, a flagellated sperm fertilizes an egg

- Cleavage commences: succession of mitotic divisions leading to the creation of a morula then ultimately a blastula

- Gastrulation creates the gastrula: a blind pouch with an opening called a blastopore

- Some animals possess larval stage and undergo metamorphosis to become adult

5. Development from zygote to animal depends on Hox genes (regulatory)

- Hox genes regulate the expression of other genes

- Ultimately involved with the fate of cells

- Body form (anatomy)

1. Tissues

- Parazoans lack true tissues

- Sponges are only extant parazoans

Important Milestones in Animal Evolution

2. Symmetry

- Some animals possess radial symmetry, while others are bilateral

- Most bilateral animals are cephalized: sensory organs at/in a head region

- the radiata are diploblastic (two germ layers)

- ectoderm & endoderm

- the bilateria are triploblastic (three germ layers)

- ectoderm, endoderm & mesoderm

3. Body Cavities

- Acoelomates have no body cavity

- Mesoderm isn’t lining digestive tract in pseudocoelomates - Coelomates have a body cavity and a digestive tract lined by the mesoderm

- a coelom has numerous functions:

- fluid cushions internal organs

- organs can move/grow independent of the body covering

- can serve as a hydrostatic skeleton

4. Protostomes vs. Deuterostomes

Table 32.1

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Within this phylum, there animals lacking backbones and animals possessing them. In either case, ALL chordates have four features.

1. Notochord

2. Dorsal, hollow nerve cord

3. Pharyngeal gill slits

4. Post-anal tail

In order to be a “member” of Phylum Chordata, you must have exhibited each of these characteristics at some point in your development.

Notochord: flexible rod that runs longitudinally through the animal

comprised of fluid-filled cells, encased in fibrous tissue

provides skeletal support

in some, notochord is reduced in adult

ex. It’s the “disc” material in human vertebrae

Dorsal, hollow nerve cord: nervous tissue that develops from the embryonic ectoderm.

most non-chordates have a solid, ventrally located, nerve cord

becomes the CNS in vertebrates

Pharyngeal gill slits: connect the animal’s pharynx to the outside.

allows water to enter the animal’s mouth and exit without entering the digestive system

used/modified in various ways: feeding, respiration

Post-anal tail: muscular in most chordates and extends past the anus

compare to non-chordates that have a full body-length digestive system

contains skeletal and muscular elements

used for propulsion in many aquatic species

• Invertebrate chordates

Class Amphibia

• Undergo a metamorphosis from a swimming larval tadpole stage to a terrestrial adult.Even though adult amphibians are terrestrial, they cannot venture far from water.

respiration

eggs would desiccate

• Amphibians usually similar anatomy to other vertebrate chordates

• Huge difference is that their heart is three-chambered (one ventricle, two atria)

Class Reptilia

• Success is due to the amniotic egg

• Extraembryonic membranes provide structures involved with gas exchange, waste storage, and nutrient storage

• Desiccation is prevented

• Reptiles are referred to as ectotherms

• Do not use metabolism to heat bodies

• Compare to endotherms

• Four-chambered heart first appears in some reptiles

• TOTAL separation of oxygenated and deoxygenated blood

• Scales rather than skin

Class Aves

• Almost every aspect of a bird’s anatomy is adapted for flight, including its feathers

• Feathers, made of keratin, are very light and strong

Class Mammalia

• Mammals are distinguished by the presence of mammary glands which produce milk to nourish young

• MOST (almost all) have hair made of keratin

• Most are born (not hatched) and possess relatively large brains making them capable of learning

1. Monotremes – reptile-like egg, no nipples (platypuses and echidnas)

2. Marsupials – born “early” and completes development in the mother’s pouch (kangaroos, koalas, etc.)

3. Eutherians – development “completed” in placenta in mother

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