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

All arthropods have jointed appendages. 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

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

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. Copyright Pearson Prentice Hall

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

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 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

Form and Function in Arthropods Excretion In aquatic arthropods, diffusion moves wastes from the body into the surrounding water. Copyright Pearson Prentice Hall

Form and Function in Arthropods Response   Most arthropods have a well-developed nervous system. All arthropods have a brain. Two nerves connect the brain to a ventral nerve cord. Along this nerve cord are several groups of nerve cells called ganglia.These ganglia coordinate the movements of individual legs. 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

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

Form and Function in Arthropods Reproduction    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

Copyright Pearson Prentice Hall 28–2 Groups of Arthropods Photo Credit: ©Skip Moody/Dembinsky Photo Associates Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 28–2 Groups of Arthropods Arthropods are classified based on the number and structure of their body segments and appendages—particularly their mouthparts. The three major groups of arthropods are: crustaceans spiders and their relatives insects and their relatives Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans What are the distinguishing features of the crustaceans? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans Crustaceans Crustaceans are primarily aquatic. This subphylum includes crabs, shrimps, lobsters, crayfishes, and barnacles. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans Crustaceans typically have two pairs of antennae, two or three body sections, and chewing mouthparts called mandibles. Abdomen Cephalothorax Crustaceans typically have two pairs of antennae, two or three body sections, and chewing mouthparts called mandibles. Notice these structures in this illustration of a crayfish, an aquatic crustacean. Each of the smaller antennae has two branches. Mandible First antenna Second antenna Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans The crayfish has a body plan that is typical of many crustaceans. The anterior cephalothorax is formed by fusion of the head with the thorax. Cephalothorax Crustaceans typically have two pairs of antennae, two or three body sections, and chewing mouthparts called mandibles. Notice these structures in this illustration of a crayfish, an aquatic crustacean. Each of the smaller antennae has two branches. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans The thorax lies just behind the head and houses most of the internal organs. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans The abdomen is the posterior part of the body. Abdomen Crustaceans typically have two pairs of antennae, two or three body sections, and chewing mouthparts called mandibles. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans The carapace is the part of the exoskeleton that covers the cephalothorax. Crustaceans typically have two pairs of antennae, two or three body sections, and chewing mouthparts called mandibles. Carapace Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans In a crustacean, the first two pairs of appendages are antennae. First antenna Crustaceans typically have two pairs of antennae, two or three body sections, and chewing mouthparts called mandibles. Each of the smaller antennae has two branches. Second antenna Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans The third pair of appendages are the mandibles. A mandible is a mouthpart adapted for biting and grinding food. Crustaceans typically have two pairs of antennae, two or three body sections, and chewing mouthparts called mandibles. Mandible Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans Decapods have five pairs of legs. In crayfishes, the first pair of legs, called chelipeds, have large claws that catch, pick up, crush, and cut food. Crustaceans typically have two pairs of antennae, two or three body sections, and chewing mouthparts called mandibles. Cheliped Cheliped Walking legs Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans Behind these legs are four pairs of walking legs. Cheliped Walking legs Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans Along the abdomen are several pairs of swimmerets, which are flipperlike appendages used for swimming. Swimmerets Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Crustaceans The final abdominal segment is fused with a pair of paddlelike appendages to form a large, flat tail. Tail Copyright Pearson Prentice Hall

Spiders and Their Relatives What are the distinguishing features of spiders and their relatives? Copyright Pearson Prentice Hall

Spiders and Their Relatives Horseshoe crabs, spiders, ticks, and scorpions are chelicerates. Chelicerates lack antennae. Copyright Pearson Prentice Hall

Spiders and Their Relatives Chelicerates have mouthparts called chelicerae and two body sections, and nearly all have four pairs of walking legs. Spiders and Their Relatives Chelicerates have special mouthparts called chelicerae and two body segments, and nearly all have four pairs of legs. Fanglike chelicera Copyright Pearson Prentice Hall

Spiders and Their Relatives Chelicerates have two pairs of appendages attached near the mouth that are adapted as mouthparts. 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. Fanglike chelicera Copyright Pearson Prentice Hall

Spiders and Their Relatives Chelicerae contain fangs and are used to stab and paralyze prey. 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. Fanglike chelicera Copyright Pearson Prentice Hall

Spiders and Their Relatives Pedipalps are longer than the chelicerae and are usually modified to grab prey. Chelicerates have special mouthparts called chelicerae and two body segments, and nearly all have four pairs of legs. Pedipalp Copyright Pearson Prentice Hall

Spiders and Their Relatives Chelicerates are divided into three main classes. Merostomata includes horseshoe crabs. Pycnogonida includes sea spiders. Arachnida, or arachnids, includes spiders, mites, ticks, and scorpions. Horseshoe crabs and sea spiders are both marine organisms. Copyright Pearson Prentice Hall

Spiders and Their Relatives Horseshoe Crabs Horseshoe crabs are found in shallow water on soft sandy or muddy bottoms. There has been a decline in number of individuals, as a consequence of coastal habitat destruction and pollution. They have chelicerae, five pairs of walking legs, and a long spikelike tail that is used for movement. While they can swim upside down, they usually are found on the ocean floor searching for worms and molluscs, which are their main food. They may also feed on crustaceans and even small fish. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Horseshoe crab Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Horseshoe crab Copyright Pearson Prentice Hall

Spiders and Their Relatives Sea Spiders Sea spiders have long legs in contrast to a small body size. The number of walking legs is usually eight (four pairs), but species with five and six pairs exist. Because of their small size and slender body and legs, no respiratory system is necessary, with gases moving by diffusion. A proboscis allows them to suck nutrients from soft- bodied invertebrates, and their digestive tract has diverticula extending into the legs. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Sea spider Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 28–2 The two main groups of chelicerates are spiders and scorpions. horseshoe crabs and spiders. horseshoe crabs and arachnids. arachnids and insects. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 28–2 Insects are part of the group crustaceans. uniramians. chelicerates. diplopods. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 28–2 Most mites and ticks are parasites. predators. herbivores. detritovores. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 28–2 Which of the following is NOT a typical crustacean characteristic? either two or three body segments chewing mouthparts called mandibles chelicerae that paralyze prey two pairs of antennae Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 28–2 Spiders differ from the other arachnids because they have two major body segments and six legs. three major body segments and eight legs. two major body segments and eight legs. three major body segments and six legs. Copyright Pearson Prentice Hall

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