Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall
Biology Copyright Pearson Prentice Hall

28-1 Introduction to the Arthropods
Photo Credit: ©Skip Moody/Dembinsky Photo Associates Copyright Pearson Prentice Hall

What Is an Arthropod? What are the main features of arthropods? Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

What Is an Arthropod? All arthropods have jointed appendages. Appendages are structures that extend from the body wall. Legs and antennae are appendages. Copyright Pearson Prentice Hall

Evolution of Arthropods
What are the important trends in arthropod evolution? Copyright Pearson Prentice Hall

A typical primitive arthropod was composed of many identical segments, each carrying a pair of appendages. Fossilized Trilobites Photo Credit: ©John Canculosi/DRK Photo. Trilobites, such as the fossilized one shown above, were marine arthropods that were abundant more than 500 million years ago. They were divided into many body segments, each with a walking leg. Copyright Pearson Prentice Hall

This early body plan was modified gradually. Body segments were lost or fused over time. Trilobites, such as the fossilized one shown above, were marine arthropods that were abundant more than 500 million years ago. They were divided into many body segments, each with a walking leg. Trilobites became extinct some 200 million years ago. Living arthropods generally have fewer body segments and more specialized appendages than ancestral arthropods. Copyright Pearson Prentice Hall

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

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

Respiration Most terrestrial arthropods breathe through a network of branching tracheal tubes that extend throughout the body. Tracheal tubes Tracheal tubes The grasshopper has organ systems typical of most arthropods. These organ systems carry out functions such as circulation, excretion, response, and movement. Arthropods have several different types of respiratory organs. In insects, tracheal tubes (inset) move air throughout the tissues of the body. Copyright Pearson Prentice Hall

Air enters and leaves the tracheal tubes through spiracles, which are small openings located along the side of the body. Spiracles Spiracles The grasshopper has organ systems typical of most arthropods. These organ systems carry out functions such as circulation, excretion, response, and movement. Arthropods have several different types of respiratory organs. Copyright Pearson Prentice Hall

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 Chelicerates have special mouthparts called chelicerae and two body segments, and nearly all have four pairs of legs. Spiders such as the one drawn here have chelicerae that are modified into fangs that can pierce and stun or even kill prey. Book lung Airflow Copyright Pearson Prentice Hall

Most aquatic arthropods, such as lobsters and crabs, respire through featherlike gills. Horseshoe crabs respire through book gills. Copyright Pearson Prentice Hall

Circulation Arthropods have an open circulatory system. The heart pumps blood through arteries that branch and enter the tissues. Heart The grasshopper has organ systems typical of most arthropods. These organ systems carry out functions such as circulation, excretion, response, and movement. Arthropods have several different types of respiratory organs. Copyright Pearson Prentice Hall

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 The grasshopper has organ systems typical of most arthropods. These organ systems carry out functions such as circulation, excretion, response, and movement. Arthropods have several different types of respiratory organs. Copyright Pearson Prentice Hall

Excretion Most terrestrial arthropods dispose of nitrogenous wastes using Malpighian tubules. Copyright Pearson Prentice Hall

Malpighian tubules are saclike organs that extract wastes from the blood and then add them to digestive wastes. Malpighian tubules The grasshopper has organ systems typical of most arthropods. These organ systems carry out functions such as circulation, excretion, response, and movement. Arthropods have several different types of respiratory organs. Copyright Pearson Prentice Hall

In aquatic arthropods, diffusion moves wastes from the body into the surrounding water. Copyright Pearson Prentice Hall

Brain Response Most arthropods have a well-developed nervous system. All arthropods have a brain. The grasshopper has organ systems typical of most arthropods. These organ systems carry out functions such as circulation, excretion, response, and movement. Arthropods have several different types of respiratory organs. Copyright Pearson Prentice Hall

Two nerves connect the brain to a ventral nerve cord. Nerve cord Copyright Pearson Prentice Hall

Along this nerve cord are several groups of nerve cells called ganglia. These ganglia coordinate the movements of individual legs and wings. Ganglia Copyright Pearson Prentice Hall

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 Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

At each body joint, different muscles either flex (bend) or extend (straighten) the joint. Flexed This diagrammatic representation shows how muscles attached to the exoskeleton bend and straighten the joints. (Actual muscles are much larger than those shown here.) Extended Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

Growth and Development in Arthropods
What happens when an arthropod outgrows its exoskeleton? Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

28–1 Copyright Pearson Prentice Hall

28–1 The mouthparts of arthropods are similar in all species. adapted to enable different species to eat different foods. adapted to enable different species to respire in different ways. useful for locomotion as well as feeding. Copyright Pearson Prentice Hall

28–1 Arthropods have open circulatory systems, which means that blood leaves the blood vessels, flows through sinuses, and then returns to the heart. flows from the heart directly into sinuses and then returns to the heart. never leaves the circulatory system. vessels open to the external environment. Copyright Pearson Prentice Hall

28–1 Characteristics which define the arthropods include an endoskeleton made of chitin and jointed appendages. an endoskeleton made of chitin and six pairs of appendages. an exoskeleton made of chitin and jointed appendages. an exoskeleton made of chitin and Malpighian tubules. Copyright Pearson Prentice Hall

28–1 What type(s) of fertilization do terrestrial arthropods have? internal external both internal and external hermaphroditic Copyright Pearson Prentice Hall

28–1 What happens to the exoskeleton of an arthropod as the animal grows? It remains soft until the animal reaches adulthood. It develops additional body segments. It softens and stretches to a larger size. It is discarded and replaced by a new, larger exoskeleton. Copyright Pearson Prentice Hall

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