Transcript Chapter 30
Chapter 30 Arthropods I. Features of Arthropods • A typical arthropod is a segmented, coelomate invertebrate animal with bilateral symmetry, an exoskeleton, and jointed structures called appendages. • A. Jointed appendages: “joint foot”=arthropoda • An appendage is any structure, such as a leg , an antenna, or mouthpart that grows out of the body of an animal. What is an arthropod? • Joints also allow powerful movements of appendages, and enable an appendage to be used in many different ways. • Mouthparts have sucking, ripping or chewing parts Origins of Arthropods Origins of Arthropods • Arthropods most likely evolved from an ancestor of the annelids. • Oldest, best –preserved multicellular animal fossils • 600 million years old • Most numerous early arthropod: trilobites • -became extinct about 250 million years ago • Lived in the sea • Segmented bodies • Jointed appendages • First animals with eyes capable of forming images. • First terrestrial arthropods: scorpions The total number of arthropods • Exceeds that of all other kinds of animals combined . • 5,000,000 species • More species of beetles than vertebrates. • Size varies from 80 micrometers (parasitic mite)to 3.6 m (giant crab found in the sea near Japan.) Two main groups •Arthropods with jaws 1.-Uniramia – (subphylum) insects chilopoda and diplopoda 2. Crustacea- (subphylum) shrimp, crab lobster •Arthropods with fangs and pincers 1. Chelicerata (subphylum) – scorpions, mites, spiders ***Each subphyla represents a distinct evolutionary line. Arthropod Body Plan Segmentation in arthropods • In most groups of arthropods, segments have become fused into three body sections—head, thorax (mid body region), and abdomen. • Individual body segments often exist only in larval stages. (ex: catepillar) Segmentation in arthropods • In other groups, even these segments may be fused. • Some arthropods have a head and a fused thorax and abdomen. Segmentation in arthropods • In other groups, there is an abdomen and a fused head and thorax called a cephalothorax. • Fusion of the body segments is related to movement and protection. Arthropods have acute senses • A compound eye is a visual structure with many lenses. • See motion much more quickly than humans. • Accurate vision is also important to the active lives of arthropods. • Most arthropods have one pair of large compound eyes and three to eight simple eyes. • A simple eye is a visual structure with only one lens that is used for detecting light. • In dragonflies and locusts, these simple eyes function as horizon detectors. –helps them stabilize their position in flight. Arthropod exoskeletons provide protection • The exoskeleton is a hard, thick, outer covering made of protein and chitin (KI tun). • Brittle and can break easily Arthropod exoskeletons provide protection • In some species, the exoskeleton is a continuous covering over most of the body. • In other species, the exoskeleton is made of separate plates held together by hinges. • Crustaceans : thick relatively inflexible exoskeleton. • Insects and arachnids: soft and flexible exoskeleton. Arthropod exoskeletons provide protection • The exoskeleton protects and supports internal tissues and provides places for attachment of muscles. • In many aquatic species, the exoskeletons are reinforced with calcium carbonate. Why arthropods must molt • Exoskeletons have their disadvantages. • First, they are relatively heavy structures. The larger an arthropod is, the thicker and heavier its exoskeleton must be to support its larger muscles. Why arthropods must molt • A second and more important disadvantage is that exoskeletons cannot grow, so they must be shed periodically. Shedding the old exoskeleton is called molting. Why arthropods must molt • When the new exoskeleton is ready, the animal contracts muscles and takes in air or water. • This causes the animal’s body to swell until the old exoskeleton splits open, usually along the back. Why arthropods must molt • Before the new exoskeleton hardens, the animal puffs up as a result of increased blood circulation to all parts of its body. • Thus, the new exoskeleton hardens in a larger size, allowing some room for the animal to continue to grow. Why arthropods must molt • Most arthropods molt four to seven times in their lives before they become adults. • When the new exoskeleton is soft, arthropods cannot protect themselves from danger because they move by bracing muscles against the rigid exoskeleton. Respiration: Arthropods have efficient gas exchange • Arthropods have efficient respiratory structures that ensure rapid oxygen delivery to cells. • This large oxygen demand is needed to sustain the high levels of metabolism required for rapid movements. Arthropods have efficient gas exchange • Three types of respiratory structures have evolved in arthropods: gills, tracheal tubes, and book lungs. Arthropods have efficient gas exchange • Aquatic arthropods exchange gases through gills, which extract oxygen from water and release carbon dioxide into the water. Arthropods have efficient gas exchange • Land arthropods have either a system of tracheal tubes or book lungs. Arthropods have efficient gas exchange • Most insects have tracheal tubes, branching networks of hollow air passages that carry air throughout the body. Arthropods have efficient gas exchange • Muscle activity helps pump the air through the tracheal tubes. • Air enters and leaves the tracheal tubes through openings on the thorax and abdomen called spiracles. Arthropods have efficient gas exchange • Most spiders and their relatives have book lungs, air-filled chambers that contain leaflike plates. Arthropods have efficient gas exchange • The stacked plates of a book lung are arranged like pages of a book. Excretion: • Most terrestrial arthropods excrete wastes through Malpighian tubules. • Slender, fingerlike extensions from the arthropods gut that are bathed in blood. • In insects, the tubules are all located in the abdomen rather than in each segment. • Malpighian tubules are attached to and empty into the intestine. • Metabolic wastes remain in the gut and leave the body through the anus. II. Spiders and other Arachnids What is an arachnid? • Spiders, scorpions, mites, and ticks belong to the class Arachnida (uh RAK nud uh). • Spiders are the largest group of arachnids. • Spiders and other arachnids have only two body regions—the cephalothorax and the abdomen. • They have no antennae • Arachnids have six pairs of jointed appendages. What is an arachnid? • The first pair of appendages, called chelicerae, is located near the mouth. chelicerae What is an arachnid? • Chelicerae are often modified into pincers or fangs. • Pincers are used to hold food, and fangs inject prey with poison. What is an arachnid? • Spiders have no mandibles for chewing. • Using a process of extracellular digestion, digestive enzymes from the spider’s mouth liquefy the internal organs of the captured prey. The spider then sucks up the liquefied food. What is an arachnid? • The second pair of appendages, called the pedipalps, are adapted for handling food and for sensing. pedipalps • Sometimes the pedipelps are for reproduction. • Following the pedipalps, are 4 pairs of appendages called walking legs. What is an arachnid? • Although all spiders spin silk, not all make webs. • Spider silk is secreted by silk glands in the abdomen. What is an arachnid? • As silk is secreted, it is spun into thread by structures called spinnerets, located at the rear of the spider. A Spider Legs Simple eyes Cocoon Pedipalps Book Lungs Silk glands Chelicerae • Spiders are predatory animals, feeding almost exclusively on other arthropods.(=carnivores) Ticks, mites, and scorpions: Spider relatives • Ticks and mites differ from spiders in that they have only one body section. tick Ticks, mites, and scorpions: Spider relatives • The head, thorax, and abdomen are completely fused. • Plant mites- while feeding may pass viral and fungal infections to plants. • Dust mites- live in carpet, bedding, clothing. (cause allergies) • Chiggers-known for their irritating bite • Ticks feed on blood from reptiles, birds, and mammals. Ticks, mites, and scorpions: Spider relatives • Mites feed on fungi, plants, and animals. • They are so small that they often are not visible to the unaided human eye. • Like ticks, mites can transmit diseases. • Lyme disease is spread by deer ticks Ticks, mites, and scorpions: Spider relatives • Scorpions are easily recognized by their many abdominal body segments and enlarged pincers.(=pedipalps) • They have a long tail with a venomous stinger at the tip. Which is used to stun their prey. Insects • Flies, grasshoppers, lice, butterflies, bees, and beetles are just a few members of the class Insecta. • Insects have three body segments (head thorax and abdomen) and six legs. • Head- mandibles (chewing mouth part) pair of antennae, compound eyes • Thorax - (composed of 3 fused segments.) • 3 pair of jointed walking legs and some have wings that are attached to the thorax. • Abdomen- is composed of 9-11 segments Arthropods have other complex body systems • The mandibles, together with other mouthparts are adapted for holding, chewing, sucking, or biting the various foods eaten by arthropods. A Grasshopper Antennae Legs Eyes Wings Spiracles Malpighian tubules Tympanum Nervous System Insect reproduction/Life Cycle • Insects usually mate once during their lifetime. • The eggs usually are fertilized internally. • Some insects exhibit parthenogenesis, reproducing from unfertilized eggs. Insect reproduction • Most insects lay a large number of eggs, which increase the chances that some offspring will survive long enough to reproduce. Metamorphosis: Change in body shape and form • After eggs are laid, the insect embryo develops and the eggs hatch. • In some wingless insects development is direct; the eggs hatch into miniature forms that look just like tiny adults. Metamorphosis: Change in body shape and form Nymph Molt Eggs Nymph Molt Adult • These insects go through successive molts until the adult size is reached. Metamorphosis: Change in body shape and form • In some cases, the adult insect bears little resemblance to its juvenile stage. Adult Egg Pupa Larva Metamorphosis: Change in body shape and form • This series of changes, controlled by chemical-substances in the animal, is called metamorphosis. • Insects that undergo metamorphosis usually go through four stages on their way to adulthood: egg, larva, pupa, and adult. Metamorphosis: Change in body shape and form • The larva is the free-living, wormlike stage of an insect, often called a caterpillar. Metamorphosis: Change in body shape and form • The pupa stage of insects is a period of reorganization in which the tissues and organs of the larva are broken down and replaced by adult tissues. • Usually the insect does not move or feed during the pupa stage. After a period of time, a fully formed adult emerges from the pupa. Metamorphosis: Change in body shape and form • The series of changes that occur as an insect goes through the egg, larva, pupa, and adult stages is known as complete metamorphosis. • Complete metamorphosis is an advantage for arthropods because larvae do not compete with adults for the same food. Metamorphosis: Change in body shape and form larvae fertilized egg • The complete metamorphosis of a butterfly is illustrated. adult pupa Metamorphosis: Change in body shape and form • Other insects that undergo complete metamorphosis include ants, beetles, flies, and wasps. Incomplete metamorphosis has three stages • Many insect species, as well as other arthropods, undergo a gradual or incomplete metamorphosis, in which the insect goes through only three stages of development. • These three stages are egg, nymph, and adult. Incomplete metamorphosis has three stages Nymph Molt Eggs Nymph Molt Adult • A nymph, which hatches from an egg, has the same general appearance as the adult but is smaller and wingless. Incomplete metamorphosis has three stages • Nymphs cannot reproduce. • As the nymph eats and grows, it molts several times. With each molt, it begins to resemble the adult more. • Gradually, the nymph becomes an adult. Incomplete metamorphosis has three stages • Grasshoppers and cockroaches are insects that undergo incomplete metamorphosis. Incomplete metamorphosis of a harlequin bug Social Insects • Two orders of insects, Hymenoptera (bees) and Isoptera (termites) have elaborate social systems. • They have division of labor. Each having their own job. (worker, drone, soldier, queen ,king) • The role played by the individual in a colony is called its caste. • Its Caste is determined by a combination of heredity, diet, hormones and pheromones Insect relatives Centipedes and Millipedes • Like spiders, millipedes and centipedes have Malpighian tubules for excreting wastes. • In contrast to spiders, centipedes and millipedes have tracheal tubes rather than book lungs for gas exchange. Centipedes and Millipedes • Centipedes are carnivorous and eat soil arthropods, snails, slugs, and worms. • Centipedes have one pair of legs /segment • The bites of some centipedes are painful to humans. Centipedes and Millipedes • A millipede eats mostly plants and dead material on damp forest floors. (herbivores) • Millipedes do not bite, but they can spray foul-smelling fluids from their defensive stink glands. • Millipedes have 2 pair of legs /segment Crustaceans • Members of the class Crustacea include crabs, lobsters, shrimps, crayfishes, water fleas, pill bugs, and barnacles. • Barnacles are sessile • Many have a distinctive larval form called a nauplius . • The nauplius has 3 pair of branched appendages and undergoes a series of molts.(pg 680) Crustaceans • Sow bugs and pill bugs, two of the few terrestrial crustaceans, must live where there is moisture, which aids in gas exchange. • Most crustaceans are aquatic and exchange gases as water flows over feathery gills. • Shrimp, water fleas, ostracods ,copepods • Copepods are among the most abundant multi-cellular organism on earth and along with krill they are a major food source in the oceans. Decapods • Crustaceans (krus TAY shuns) this type have two pairs of antennae for sensing. • 5 pairs of legs • Anterior pair of legs are modified into large pincers • Swimmerets- are called chelipeds. appendages attached • Cephalathorax (called a to the underside for carapace) swimming and reproduction • Uropods-flattened, paddle like appendages • Telson- tail spine Crustaceans claw legs • The first pair of walking legs are often modified into strong claws for defense. (Cheliped)