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Biology
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28-1 Introduction to the Arthropods
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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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28-1 Introduction to the Arthropods
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What Is an Arthropod?
What Is an Arthropod?
Arthropods have a segmented body, a tough exoskeleton, and jointed appendages.
Arthropods include insects, crabs, centipedes, and spiders.
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28-1 Introduction to the Arthropods
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What Is an Arthropod?
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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What Is an Arthropod?
All arthropods have jointed appendages.
Appendages are structures that extend from the body wall.
Legs and antennae are appendages.
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28-1 Introduction to the Arthropods
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Evolution of Arthropods
What are the important trends in arthropod evolution?
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28-1 Introduction to the Arthropods
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Evolution of Arthropods
Evolution of Arthropods
A typical primitive arthropod was composed of many identical segments, each carrying a pair of appendages.
Fossilized Trilobites
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28-1 Introduction to the Arthropods
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Evolution of Arthropods
This early body plan was modified gradually.
Body segments were lost or fused over time.
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28-1 Introduction to the Arthropods
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Evolution of Arthropods
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
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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28-1 Introduction to the Arthropods
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Form and Function in Arthropods
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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28-1 Introduction to the Arthropods
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Form and Function in Arthropods
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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28-1 Introduction to the Arthropods
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Form and Function in Arthropods
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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28-1 Introduction to the Arthropods
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Form and Function in Arthropods
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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28-1 Introduction to the Arthropods
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Form and Function in Arthropods
Most aquatic arthropods, such as lobsters and crabs, respire through featherlike gills.
Horseshoe crabs respire through book gills.
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28-1 Introduction to the Arthropods
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Form and Function in Arthropods
Circulation
Arthropods have an open circulatory system.
The heart pumps blood through arteries that branch and enter the tissues.
Heart
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Form and Function in Arthropods
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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Form and Function in Arthropods
Excretion
Most terrestrial arthropods dispose of nitrogenous wastes using Malpighian tubules.
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28-1 Introduction to the Arthropods
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Form and Function in Arthropods
Malpighian tubules are saclike organs that extract wastes from the blood and then add them to digestive wastes.
Malpighian tubules
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28-1 Introduction to the Arthropods
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Form and Function in Arthropods
In aquatic arthropods, diffusion moves wastes from the body into the surrounding water.
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Form and Function in Arthropods
Response
Most arthropods have a well-developed nervous system.
All arthropods have a brain.
Brain
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28-1 Introduction to the Arthropods
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Form and Function in Arthropods
Two nerves connect the brain to a ventral nerve cord.
Nerve cord
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28-1 Introduction to the Arthropods
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Form and Function in Arthropods
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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28-1 Introduction to the Arthropods
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Form and Function in Arthropods
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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28-1 Introduction to the Arthropods
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Form and Function in Arthropods
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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Form and Function in Arthropods
At each body joint, different muscles either flex (bend) or extend (straighten) the joint.
Flexed
Extended
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Form and Function in Arthropods
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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28-1 Introduction to the Arthropods
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Growth and Development in Arthropods
What happens when an arthropod outgrows its exoskeleton?
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28-1 Introduction to the Arthropods
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Growth and Development in Arthropods
Growth and Development in Arthropods
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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Growth and Development in Arthropods
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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Growth and Development in Arthropods
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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