End Show Slide 1 of 38 Copyright Pearson Prentice Hall Biology

Copyright Pearson Prentice Hall

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Biology


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28-1 Introduction to the Arthropods


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What Is an Arthropod?

What are the main features of arthropods?


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Arthropods have a segmented body, a tough exoskeleton, and jointed appendages.

Arthropods include insects, crabs, centipedes, and spiders.


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Arthropods are surrounded by a tough external covering, or exoskeleton.

The exoskeleton is made from protein and chitin. Chitin is a carbohydrate.


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All arthropods have jointed appendages.

Appendages are structures that extend from the body wall.

Legs and antennae are appendages.


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Evolution of Arthropods

What are the important trends in arthropod evolution?


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A typical primitive arthropod was composed of many identical segments, each carrying a pair of appendages.

Fossilized Trilobites


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This early body plan was modified gradually.

Body segments were lost or fused over time.


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The evolution of arthropods has led to fewer body segments and highly specialized appendages for feeding, movement, and other functions.


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Form and Function in Arthropods


Arthropods use complex organ systems to carry out different essential functions.

Organ systems are interrelated; the functioning of one system depends on that of other systems.


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Feeding

Arthropods include herbivores, carnivores, and omnivores. There are filter feeders, detritivores, and parasites.

The mouthparts of arthropods are adapted to the type of food the arthropod eats.


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Respiration

Most terrestrial arthropods breathe through a network of branching tracheal tubes that extend throughout the body.

Tracheal tubes

Tracheal tubes


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Air enters and leaves the tracheal tubes through spiracles, which are small openings located along the side of the body.

Spiracles Spiracles


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Other terrestrial arthropods, such as spiders, respire using book lungs.

Book lungs are organs that have layers of respiratory tissue stacked like pages of a book.

Spiracles

Airflow

Book lung


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Most aquatic arthropods, such as lobsters and crabs, respire through featherlike gills.

Horseshoe crabs respire through book gills.


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Circulation

Arthropods have an open circulatory system.

The heart pumps blood through arteries that branch and enter the tissues.

Heart


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Blood leaves the blood vessels and moves through sinuses, or cavities.

Blood collects in a large sinus surrounding the heart and re-enters the heart.

Heart


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Excretion

Most terrestrial arthropods dispose of nitrogenous wastes using Malpighian tubules.


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Malpighian tubules are saclike organs that extract wastes from the blood and then add them to digestive wastes.

Malpighian tubules


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In aquatic arthropods, diffusion moves wastes from the body into the surrounding water.


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Response

Most arthropods have a well-developed nervous system.

All arthropods have a brain.

Brain


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Two nerves connect the brain to a ventral nerve cord.

Nerve cord


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Along this nerve cord are several groups of nerve cells called ganglia.

These ganglia coordinate the movements of individual legs and wings.

Ganglia


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Most arthropods have sophisticated sense organs such as compound eyes.

Compound eyes may have more than 2000 separate lenses and can detect color and motion very well.

Compound eyes


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Movement

Arthropods move using well-developed groups of muscles that are coordinated and controlled by the nervous system.

Muscles generate force by contracting and then pulling on the exoskeleton.


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At each body joint, different muscles either flex (bend) or extend (straighten) the joint.

Flexed

Extended


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Reproduction

Terrestrial arthropods have internal fertilization.

In some species, males deposit sperm inside females.

In other species, the males deposit a sperm packet that is picked up by the females.

Aquatic arthropods may have internal or external fertilization.


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Growth and Development in Arthropods

What happens when an arthropod outgrows its exoskeleton?


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When they outgrow their exoskeletons, arthropods undergo periods of molting.

During molting, an arthropod sheds its entire exoskeleton and manufactures a larger one to take its place.


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Molting is controlled by the arthropod's endocrine system.

Most arthropods molt several times.

The arthropod is vulnerable to predators while its shell is soft.


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Skin glands digest the inner part of the exoskeleton, and other glands secrete a new skeleton.

When the new exoskeleton is ready, the animal pulls itself out of what remains of the original skeleton.


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28–1


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28–1

The mouthparts of arthropods are

a. similar in all species.

b. adapted to enable different species to eat different foods.

c. adapted to enable different species to respire in different ways.

d. useful for locomotion as well as feeding.


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28–1

Arthropods have open circulatory systems, which means that blood

a. leaves the blood vessels, flows through sinuses, and then returns to the heart.

b. flows from the heart directly into sinuses and then returns to the heart.

c. never leaves the circulatory system.

d. vessels open to the external environment.


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28–1

Characteristics which define the arthropods include

a. an endoskeleton made of chitin and jointed appendages.

b. an endoskeleton made of chitin and six pairs of appendages.

c. an exoskeleton made of chitin and jointed appendages.

d. an exoskeleton made of chitin and Malpighian tubules.


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28–1

What type(s) of fertilization do terrestrial arthropods have?

a. internal

b. external

c. both internal and external

d. hermaphroditic


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28–1

What happens to the exoskeleton of an arthropod as the animal grows?

a. It remains soft until the animal reaches adulthood.

b. It develops additional body segments.

c. It softens and stretches to a larger size.

d. It is discarded and replaced by a new, larger exoskeleton.

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End Show Slide 1 of 38 Copyright Pearson Prentice Hall Biology