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1. Explain the classification and the phylogeny of each phyla.

Evolution and Classification

Animals with arthropod characteristics evolved more then 600 million years ago. Because all arthropods possess both an exoskeleton and jointed appendages, biologists have long inferred that they all evolved from a common ancestor. However, the most current studies of arthropod structure suggest that there may actually be four separate lines of arthropod evolution. On the basis of these recent studies, arthropods are now classified by scientists into four subphyla:

• Trilobita includes extinct organisms called trilobites.

• Crustacea includes shrimp, lobsters, crabs, barnacles, cladocerans, ostracods, crayfish, water fleas, and copepods.

• Chelicerata includes spiders, scorpions, ticks, mites, sea spiders, and horseshoe crabs.

• Uniramia is the only group that seems to have evolved on land and includes centipedes, millipedes, and all of the insects

Many of the adaptations that have made insects successful are characteristics they share with other arthropods. For example, an exoskeleton, jointed appendages, and a segmented body are all common arthropod traits. However, insects are distinguished from other arthropods by the following arthropod traits:

• The body has three parts; head, thorax, and abdomen

• The head has one pair of antennae

• The thorax has three pairs of jointed legs and, in many species, one or two pairs of wings.

• The abdomen is divided into 11 segments. It has neither wings nor legs attached to it.

In spite of the characteristics they share, insect species show an enormous range of variations that have allowed them to succeed in diverse environments. These variations can be grouped into three categories. The first category consist of structural variations, such as differences in mouthparts. For example, a wasp has mouthparts adapted for chewing, while an aphid uses its mouthparts to pierce plants and suck liquids. A second group of variations, physiological variations, consists of differences in the way internal systems work. For instance, a female mosquito has enzymes that allow it to digest human blood; a grasshopper does not have these enzymes but has others that enable it to digest grass. Finally, behavioral variations are differences in the ways insects respond to their surroundings. Honeybees, for example, live in complex societies called hives. Many species of bumblebees, on the other hand, are solitary and usually live part of their lives in holes in the ground.

To make it easier to study such a vast and diverse group of organisms, taxonomists classify insects into more than 30 orders. They base their classification primarily on structural and physiological variations.

Why have the insects been such a biological success? Like other arthropods, they have benefited form evolution of an exoskeleton and jointed appendages. Additionally, they can adapt to new environments rapidly because individual insects have extremely short life spans. In many species adults live for only weeks or months. Since generations occur in rapid succession, natural selection can take place more quickly than in organisms that take longer to reproduce.

As they have evolved, insects have had a wide range of environments available to them because of their flying ability and their small size. The power of flight enables insects to disperse readily, to escape from predators, and to move to environments less accessible to other organisms. In addition, the small size of insects allows several species to inhabit different environments within a small area without competing with one another.

2. Describe the characteristics typical for the diversity shown by each phyla

Three-fourths of all animal species belong to the Phylum Arthropoda. This diverse phylum includes insects and spiders, lobsters and crabs, as well as millipedes and centipedes.

Characteristics

All members of the phylum Arthropoda share the following characteristics:

• arthropods have joined appendages. appendages are extensions of the body and include legs and antennae.

• the athropod body is segmented. a pair of appendages is attached to each segment. in some species the appendages have been lost or reduced in size during the course of evolution.

• arthropods have an exoskeleton. an exoskeleton is a hard external covering that provides protection and support.

• arthropods have a ventral nervous system, an open circulatory system, a digestive system, and specialized sensory receptors.

the name arthropod, meaning "jointed foot", refers to the jointed appendages. jointed appendages and an exoskeleton are the most distinctive arthropod traits. the exoskeleton provides much more structural support than the annelid cuticle and gives the internal organs better protection.

The chemical composition and the three-layered structure of the exoskeleton give it versatility and strength. The exoskeleton is composed primarily of protein and a tough carbohydrate called chitin. The waxy outer layer repels water and helps prevent desiccation in terrestrial species. The hard middle layer, which is strengthened by materials such as calcium, provides the primary protection. The inner layer, which is flexible at the joints, allows the animal to move freely. All three layers are secreted by an epidermis that lies just beneath them.

Movement and growth

Unlike the muscles of annelids, which form continuous sheets in the body wall, the muscles of arthropods occur in bundles that attach to the inside of the exoskeleton on either side of the joints. By alternately contracting and relaxing these muscles, the arthropod in essence operates a system of levers that move the body parts and appendages.

Because the exoskeleton cannot enlarge as the body enlarges, the exoskeleton must be shed periodically and a new one must be formed. This process is called molting. Molting is also called ecdysis. The tissues of the arthropod grow until they put a great deal of pressure on the exoskeleton walls. A hormone is then produced that induces molting.

When an arthropod starts to molt, the cells of the epidermis secrete enzymes that digest the inner, flexible layer of the exoskeleton. Simultaneously the epidermis begins to synthesize a new exoskeleton, using much of the digested material. During this process the outer layer of the old exoskeleton loosens and breaks along specific lines. The old exoskeleton is then shed. The new exoskeleton, which is flexible at first, stretches to fit the now enlarged insect.

An arthropod molts many times during the course of its lifetime. Each time it molts, it becomes larger. However, during molting it is extremely vulnerable to predators because it temporarily lacks a hard shell. Terrestrial Athropods are also susceptible to desiccation during molting. For these reasons, arthropods usually go into hiding when they molt until their new exoskeleton has hardened.

Evolution and Classification

Animals with arthropod characteristics evolved more then 600 million years ago. Because all arthropods possess both an exoskeleton and jointed appendages, biologists have long inferred that they all evolved from a common ancestor. However, the most current studies of arthropod structure suggest that there may actually be four separate lines of arthropod evolution. On the basis of these recent studies, arthropods are now classified by scientists into four subphyla:

• Trilobita includes extinct organisms called trilobites.

• Crustacea includes shrimp, lobsters, crabs, barnacles, cladocerans, ostracods, crayfish, water fleas, and copepods.

• Chelicerata includes spiders, scorpions, ticks, mites, sea spiders, and horseshoe crabs.

• Uniramia is the only group that seems to have evolved on land and includes centipedes, millipedes, and all of the insects

The four separate lines of atrhropod evolution are illustrated in the picture above. Members of the four subphyla are distinguished primarily by differences in their embryological development and differences in the morphology of structures such as appendages and mouthparts. Members of Chelicerata are distinguished from other arthropods by the absence of antenae and the presence of pincerlike mouthparts called chelicerae. Crustaceans are distinguished by the presence of branched antenae and chewing mouthparts called mandibles. The members of Uniramia are also distinguished by having antennae and mandibles, but thei appendages are unbranched. Uniramia means "one brach".

Despite their differences, the three subphyla of living arthropods have evolved similarly. For example, ancestral arthropods had one pair of appendages per segment, but most living species have fewer appendages than this. In addition, the evolution of these groups shows a general tendency toward less segmentation of the body. For example, ancestral arthropods had many segments, but most modern adults have some segments fused together into larger structures with specialized functions.

Crustacea

Members of the Subphylum Crustacea have hard exoskeletons that contain calcium carbonate. The approximately 25,000 species of crustaceans include crayfish, lobsters, pill bugs, sow bugs, water fleas, and barnacles. Crustacea is the only subphylum of modern arthropods that contains mostly aquatic members.

Diversity

Most crustaceans are small. Copepods no larger than a comma inhabit the surface waters of oceans, lakes, and streams. Barnacles are sessile crustaceans that attach themselves to rocks and pilings as well as to whales and sea turtles. Barnacles filter plankton from the water with 12 appendages called cirri.

Some crustaceans, such as sow bugs and pill bugs, are terrestrial. Because these animals have seven identical pairs of legs, they are called isopods, which means "same feet". Isopods usually live in damp areas, where their gills can stay moist.

The crayfish

Crayfish are often studied as representative crustaceans because they are large and abundant. Crayfish are similar to lobsters in their internal and external structures.

External Structure

The body of the crayfish is divided into two sections, the cephalothorax and the abdomen. The cephalothorax consists of the fused head and the thorax; it has 13 segments and is covered by a hard carapace. The abdomen is divided into seven segments. The seventh segment, called the telson, forms a flat triangular section at the tail of the animal. Powerfull abdominal muscles can jerk this tail and propel the animal rapidly backward.

Appendages and Function

Antennules - Appendages with receptors for touch, taste and equilibrium

Antennae - Specialized for touch and taste

Mandibles - Move up and down to crush food

Maxillae - Move side to side to tear food

Maxillipeds - "Jaws to hold food"

Chelipeds - Claws that capture food and serve as defensive weapons

Walking legs - Enable the crayfish to walk slowly

Swimmerets - Create water currents; function in reproduction

Uropods - Propel crayfish through water

Digestive and Excretory Systems

Crayfish trap food with their chelipeds, tear it with their maxillae and maxillipeds, and chew it with the mandibles. The food then passes through the esophagus to the stomach, where chitinous teeth grind it into a fine paste that is mixed with digestive juices. Digestive glands absorb the mixture, and undigested particles pass through the intestines and out the anus. Excretory organs, called green glands, remove wastes from the blood and retain salts, which are scarce in fresh water.

Circulatory and Respiratory Systems

The crayfish has an open circulatory system. Blood flows from a dorsal sinus through small, one-way valves called ostia into the dorsal hearth. The hearth then pumps the blood into seven large vessels that carry it through the body. Blood leaves the vessels and fills the body cavity, where it bathes the organs and cells. Blood collects in a large ventral sinus. Other vessels than carry the blood through the gills, where it gives off carbon dioxide and takes up oxygen gas. It then returns to the dorsal sinus.

Gills are attached to each walking leg, protected in a chamber under the carapace. As the crayfish walks, water moves across the gills. Also, as the second maxillae move during feeding, the two gill bailers attached to them "bail" water over the gills.

Nervous system

The crayfish nervous system includes a brain and a central nerve cord that runs from the brain to the tail. Nerve impulses travel to and from the nerve cord through ganglia. Nerves connect the brain with sense receptors in the antennules, antennae, and eyes.

The eyes are set on two short, movable stalks. Each eye has more than 2000 light-sensitive lenses. Eyes with many lenses, or compound eyes, are highly sensitive to light and detect motion well, even thought they can form only very crude images.

A crustacean senses position through the use of statocysts. Statocysts are cells that contain particles of calcium carbonate, which move when the crustaceans position changes. This movement is monitored by the nerves and interpreted by the brain.

Reproduction and Development

Crayfish usually mate in the fall. The male uses its first and second pair of swimmers to transfer sperm to the seminal receptacle of the female. The sperm remains there until spring, when it fertilizes the eggs as the female lays them. A sticky secretion attaches the eggs to the last three pairs of the females swimmerets. The eggs hatch after about six weeks, having gone through several larval stages. The young look like tiny adults. They mold repeatedly - an average of seven times during the first year, then twice a year for the remaining two or three years of their lives.

Other Arthropods

Unlike crustaceans, nearly all members of Chelicerata and Uniramia are terrestrial.

Arachnida

The class Arachnida is a group of more than 100,000 species, including spiders, scorpions, and mites. Most arachnids are adapted to kill pray with poison glands, stingers, or fangs.

Like crustaceans, arachnids have a body that is divided into a cephalothorax and an abdomen. Attached to the cephalothorax are four pairs of legs, a pair of chelicerae, and a pair of appendages called pedipalps. The pedipalps aid in chewing; in some species pedipalps are specialized to perform other functions.

Diversity

Spiders range in length from less than 0.5 mm to 9 cm in some tropic tarrantula species. Spiders feed mainly on insects. Various species of spiders are adapted to capture pray in different ways. Some chase after pray, some catch prey in "trapdoors" in the ground, and some snare pray in elaborate webs.

Most scorpions live in tropical or semitropical areas; others live in dry temperate or desert regions. Scorpions differ from spiders in two ways. Scorpions have greatly enlarged pedipalps , which they hold in a forward position. They also have a large stinger over the head. Most scorpions hide during the day and hunt at night. Scopions seize their prey with their pincerlike pedipalps. Then the stinger injects paralyzing venom, the chelicerae tear the prey, the animal is ingested, and digestion begins. Only a few species have a sting that may be fatal to humans.

Unlike other arachnids, mites and ticks have a fused cephalothorax and abdomen. Mites and ticks are the most abundant and most specialized arachnids. Ticks range in size from a few millimeters to 3 cm; most mites are less than a millimeter long.

Some mites and ticks are pests; others transmit diseases. Spider mites damage fruit trees when they suck fluid from the leaves. Many parasitic ticks pierce their host’s skin to feed on blood. In the process they can transmit organisms such as those that cause rocky mountain spotted fewer.

Structure and Function

Arachnids share many characteristics with crustaceans. For example, their nervous, digestive, and circulatory systems of both groups are structurally similar. However, arachnids are terrestrial and therefore have a unique respiratory system. Spiders respire through openings in the cuticle called spiracles. Air passes through the spiracles to the book lungs, the tracheae, or both. Book lungs, paired sacs in the abdomen with pagelike components, provide a large surface area for the exchange of gases. Tracheae carry air directly to the tissues.

The excretory system is also modified for life on land. The main excretory organs, called Malpighian tubules, are hollow projections of the digestive tract that collect body fluids, remove wastes, and carry wastes to the intestines. Most of the water is then reabsorbed, and the solid wastes leave the body. Some spiders also have coxal glands, organs that remove wastes and discharge them through an opening at the base of the leg.

Spiders have eight simple eyes rather than compound eyes. Many spiders also spin webs. The posterior tip of their abdomen contains three pairs of spinnerets, each made up of hundreds of microscopic tubes. Fluid from silk glands passes through the tubes and hardens into a thread that can be spun into webs. Silk is also used to built nests and egg cocoons. The young of some species use a long thread as a balloon to ride the wind to new habitats.

In reproduction, a male gathers sperm in special sacs in the tips of his pedipalps. He places the sperm in the seminal receptacle of the female. Later the female lays eggs, which are fertilized by the stored sperm as they pass through the genital pore. The female then seals the eggs in a case of silk. The young spiders go through their first mold inside the case.

Myriapods

Centipedes and millipedes are collectively called myriapods, which means "many feet". Myriapods, along with insects, are members of the Subphylum Uniramia. All centipedes and millipedes do not have a waxy cuticle. They retain moisture through behavioral adaptations, such as living in damp environments to prevent desiccation.

Millipedes

Millipedes are members of the Class Diplopoda. The term millipede means "many feet". Millipedes have two pairs of legs on each body segment except the last two. Although millipedes have many legs, they have far fewer than a thousand. The legs of a millipede are strong and well adapted for burrowing through humus and soil. However, these legs are also short, which makes them slow. When threatened, a millipede rolls its body into a coil and may also spray a noxius chemical that contains cyanide.

In cross section the bodies of the millipedes are rounded. They live in soil, in logs, and under objects. Many have a strong sense of smell but poor vision. Millipedes are herbivores adapted for chewing plants and decayed matter in the soil.

Centipedes

Centipedes are members of the class Chilopoda. The term cetnipede means "hundred legs". Centipedes differ from millipedes by having the body flattened in cross section. They also have only one pair of legs per segment, except the first one and last two. They can also move faster because their legs are longer. Many coil up for defense. Centipedes may have anywhere from 15 to 175 pairs of legs. Voracious predators, centipedes feed on earthworms and on insects such as cockroaches. The first body segment has a pair of clawlike appendages that can inject venom into prey.

Insects

Characteristics and Clasification

Many of the adaptations that have made insects successful are characteristics they share with other arthropods. For example, an exoskeleton, jointed appendages, and a segmented body are all common arthropod traits. However, insects are distinguished from other arthropods by the following arthropod traits:

• The body has three parts; head, thorax, and abdomen

• The head has one pair of antennae

• The thorax has three pairs of jointed legs and, in many species, one or two pairs of wings.

• The abdomen is divided into 11 segments. It has neither wings nor legs attached to it.

In spite of the characteristics they share, insect species show an enormous range of variations that have allowed them to succeed in diverse environments. These variations can be grouped into three categories. The first category consist of structural variations, such as differences in mouthparts. For example, a wasp has mouthparts adapted for chewing, while an aphid uses its mouthparts to pierce plants and suck liquids. A second group of variations, physiological variations, consists of differences in the way internal systems work. For instance, a female mosquito has enzymes that allow it to digest human blood; a grasshopper does not have these enzymes but has others that enable it to digest grass. Finally, behavioral variations are differences in the ways insects respond to their surroundings. Honeybees, for example, live in complex societies called hives. Many species of bumblebees, on the other hand, are solitary and usually live part of their lives in holes in the ground.

To make it easier to study such a vast and diverse group of organisms, taxonomists classify insects into more than 30 orders. They base their classification primarily on structural and physiological variations.

The Sucess of Insects

Insects live almost everywhere in the world except in the deep ocean. Water striders live on the surface of oceans and lakes, and beetles live in the hottest desserts. Snowfleas survive on permanent glaciers on the world's highest mountains. Closer to our home, we may find aphids on the leaves of garden plants or beetles under the bark of trees. .

Arthropoda is the largest animal phylum, and Insecta is by far the largest class within this phylum. Entomologists, or scientists who study insects, have classified more than 700,000 insect species. Every year biologists describe thousands of new species. Based on current knowledge, some entomologists estimate that as many as 10 million insect species exist.

Common Insect Orders

Order

Number of Species

Examples

Characteristics

Significance to humans

Orthoptera

("streight-wing")

23,000

Grasshoppers

Crickets

Katydids

Cockroaches

Two pairs of straight wings; chewing mouthparts

Cause damage to crops; pests in houses

Isoptera

("equal-wing")

1,800

Termites

Two pairs of membranous wings; chewing mouthparts

Destroy wood in forests and buildings; recycle resources in forests

Dermaptera

("skin-wing)

1,100

Earwigs

One or two pairs of wings; chewing mouthparts; pincerlike appendages at the tip of abdomen

Damage crops and garden plants

Anoplura

("unarmed-tail")

200

sucking lice

Wingless; piercing sucking mouthparts

Parasite humans and other mammals; carry disease

Hemiptera

("half-wing")

40,000

All true bugs

Two pairs of membranous wings during part of life; piercing, sucking mouthparts

Damage plants; carry disease

Homoptera

("like-wing")

20,000

Aphids

Mealy bugs

Cicadas

Membranous wings held like roof over body (some species wingless); piercing, sucking mouthparts

Damage crops and gardens

Ephemeroptera

("for-a-day-wing")

1,500

Mayflies

Membranous wings (forewings triangular); nonfunctioning mouthparts in adults

Serve as food for freshwater fish

Odonata

("toothed")

5,000

Dragonflies

Damselflies

Two pairs of long, narrow, membranous wings; chewing mouthparts

Destroy harmful insects

Neuroptera

("nerve-wing")

4,600

Dobsonflies

Lacewings

Two pairs of membranous wings; mouthparts sucking in larvae, chewing in adults

Destroy harmful insects

Coleoptera

("sheath-wing")

280,000

Weevils

Ladybugs

Beetles

Hard forewings, membranous hindwings; sucking or chewing mouthparts

Destroy crops; prey on other insects

Lepidoptera

("scale-wing")

110,000

Butterflies

Moths

Large, scaled wings; mouthparts chewing in larvae, siphoning in adults

Pollinate flowers; produce silk; damage clothing and crops

Diptera

("two-wing")

85,000

Mosquitoes

Flies

Gnats

One pair of wings; sucking, piercing, or lapping mouthparts

Carry disease

Siphonaptera

("tube-wingless")

1,100

Fleas

Wingless in adults; mouthparts chewing in larvae, sucking in adults

Parasitize birds and mammals; carry disease

Hymenoptera

("membrane-wing")

100,000

Bees

Wasps

Ants

Two pairs of membranous wings ( some species wingless); chewing, sucking, or lapping mouthparts; some species social

Pollinate flowers; make honey

Why have the insects been such a biological success? Like other arthropods, they have benefited form evolution of an exoskeleton and jointed appendages. Additionally, they can adapt to new environments rapidly because individual insects have extremely short life spans. In many species adults live for only weeks or months. Since generations occur in rapid succession, natural selection can take place more quickly than in organisms that take longer to reproduce.

As they have evolved, insects have had a wide range of environments available to them because of their flying ability and their small size. The power of flight enables insects to disperse readily, to escape from predators, and to move to environments less accessible to other organisms. In addition, the small size of insects allows several species to inhabit different environments within a small area without competing with one another.

Insects and Human Society

Since insects are so abundant, it is not surprising that they effect human society in many ways. A small minority of insect species cause severe problems for people. Boll weevils, corn earthworms, and other agricultural pests compete with humans for food by eating crops. Other insect spread diseases. In the tropics female mosquitoes transmit Plasmodium, the protozoan that causes malaria. Flies transfer the bacterium Salmonella typhi, which causes typhoid fewer.

In spite of the problems some insects cause, it would be a serious mistake to think that the world would be better off without them. Insects play many vital roles in the environment. For example, insects pollinate more than two-thirds of the world’s flowering plants; they also serve as food for a multitude of fish, birds and mammals. We tend to think of termites as destructive pests. However, in feeding on decaying wood, they help recycle materials needed to maintain a healthy forest. Honey, silk, and shellac are some products produced by insects. Without insects to pollinate many of our crop plants, our food sources would be greatly diminished.

External Structure

The African Goliath beetle grows to more than 10 cm in length, and the atlas moth has a wingspan of more than 25 cm. However, most insects are far smaller. Among the smallest is the fairy fly, which measures 0.2 mm in length.

Like all insects the grasshopper has three body segments. The anterior segment is the head. It contains the brain and bears many of the sensory organs, such as the antenae and compound eyes. The head also has complex mouthparts that are used for gathering food. The middle segment is the thorax, to which the legs and wings are attached. The posterior segment is the abdomen, which is often specialized for reproduction and has structures for digestion, respiration, and excretion.

The thorax consists of three parts: prothorax, mesothorax, and metathorax. The prothorax and mesothorax each have a pair of walking legs that allow the grasshopper to creep along blades of grass. Attached to the metathorax is a pair of jumping legs that enables the grasshopper to leap away from danger and to launch into fight. Spines, hooks, and pads on each foot, or tarsus, provide the grasshopper with grip.

The grasshopper has two pairs of wings. A pair of leathery forewings covers and protects the hindwings when the grasshopper isn’t flying. Although the forewings can help the grasshopper glide during flight, it is the movement of the hindwings that actually propels the insect through the air. The grasshopper can move its wings because of muscles attached to the inside of it sexoskeleton. The forewings are attached to the mesothorax; the hind wings are attached to the metathorax.

Internal structure

Many structural and physiological adaptations can be observed by examining an insect’s organ systems.

Digestive and Excretory systems

Grasshoppers feed on blades of grass, and the jaws of grasshoppers are thus modified for cutting and chewing. The liplike labium and labrum help hold the grass in position so that the rough edged jaws called mandibles can tear off edible bits. Behind the mandibles are the maxillae, a second set of jaws that helps hold and cut the food.

In the mouth food is moistened by saliva from the salivary glands. The moistened food then passes through the esophagus and into the crop for temporary storage. From the crop, food passes into the gizzard, where sharp chitinous plates shred it. The shredded mass then passes into the insect’s stomach, called the midgut. There the food is bathed in enzymes secreted by pockets of the stomach called the gastric ceca. Digested matter then flows through the midgut wall and into the coelom, or body cavity, and is distributed by the circulatory system.

Undigested matter from the midgut travels into the hindgut, made up of the colon and the rectum. Meanwhile, wastes from the cells have been picked up by the blood. Malphighian tubules in the hindgut remove chemical wastes from the blood and deposit them in the rectum. All wastes then leave through the anus.

Circulatory system

Digested food and other materials reach the grasshoppers cells through an open circulatory system like that of the crayfish. Blood flows through a large vessel called the aorta. Muscular regions of the aorta, often called the grasshopper’s hearths, are located in the posterior abdomen. They pump the blood forward through the aorta and into the part of coelom near the head. The blood then flows back through the coelom toward the abdomen, carrying digested food to the organs. At the same time, the blood transfers cellular wastes to the Malpighian tubules and then completes the circuit back to the aorta through pores called ostia.

Respiratory System

Insects do not breathe with lungs or gills but instead take in air through tiny openings on the abdomen and thorax called spiracles. As muscles expand plates on the grasshopper’s abdomen, air flows through the spiracles and enters a network of air tubes called tracheae. In insects oxygen travels directly to body tissues through the tracheae and their smaller branches. In most other animals oxygen is transported by the blood. When the abdomen contracts, waste gases that have diffused out of cells collect in the tracheae. These waste gases are then expelled through the spiracles.

Nervous System

The grasshopper has a complex internal nervous system connected to the external sensory organs. Three simple eyes arranged in a row just above the base of the antennae serve simply to detect light. two bulging compound eyes composed of hundreds of six sided lenses allow the insect to see in several directions at once. They can detect movement but cannot produce sharply focused images. Grasshopper sense sounds by means of a small, nerve-rich cavity located along the first abdominal segment. This cavity is covered with a sound-sensing membrane called a tympanum. Sense organs for both touch and smell are located on the antennae and elsewhere on the body.

If you’ve ever tried to catch a grasshopper, you have seen the effect of its nervous system in action. The grasshopper’s eyes detect movement. Nerve impulses travel up nerve cords to the nerve ganglia that form the brain. Messages from the ganglia travel rapidly down other nerve cords to the muscles that control the jumping legs. The legs flex, and in an instant the grasshopper is out of the persons grasp.

Reproductive system

The reproductive organs of both male and female grasshoppers are located in the abdomen. During mating the male grasshopper deposits sperm into the female’s seminal receptacle, a storage pouch that holds the sperm until eggs are released. After release the eggs are fertilized internally. The female grasshopper uses two pairs of pointed organs called ovipositors to dig a nest hole in the soil and to deposit the eggs.

Defense

Insects have many defensive adaptations that enhance survival. Some adaptations are for aggressive defense. One of the most elaborate is that of bombardier beetle, which sprays predators with a hot stream of a noxious chemical. The beetle can even rotate an opening on its abdomen to aim the spray at its attacker. A more common defense is the barbed stinger of bees and wasps.

Some adaptations provide a passive defense. The grasshopper grassy green color is a good example of passive defense - camouflage, or the ability to blend into surroundings. Camouflage enhances survival by making it difficult for predators to spot the insect. An remarkable form of camouflage is exhibited by the many species of "stick insects". These creatures look so much like twigs that they often cannot be seen unless they move. Other insects defend themselves not by hiding but by advertising. Many poisonous or bad-tasting insects evolved warning coloration - bold, bright color patterns that make them clearly recognizable and warn predators away.

In some cases evolution has resulted in several poisonous or dangerous species having similar patterns of warning coloration. This adaptation, called Müllerian mimicry, encourages predators to avoid all of these species. For example, many species of stinging bees and wasps have a similar pattern of black and yellow stripes. In other cases insects that are neither poisonous nor bad-tasting have patterns that fool predators by mimicking the coloration of other species. For example, the viceroy butterfly looks much alike the unpleasant-tasting monarch. This type of defensive adaptation is called Batasian mimicry.

3. Describe the life cycles typical for the organisms in this phylum

Devalopment

Insects go through a number of stages before they reach their adult forms. Only silverfish and few other insects start out a smaller versions of adult insects. Most insects undergo distinct changes in both form and size as they develop. This series of changes is called metamorphosis. Metamorphosis is the result of the process of gene expression.

Incomplete Metamorphosis

Grasshoppers, termites, and some other insects go through a pattern of development called incomplete metamorphosis. This process has three stages: egg, nymph and adult. When the egg hatches, a nymph emerges. A nymph is an immature form that looks somewhat like the adult, but is smaller, has undeveloped reproductive organs, and lacks wings. The nymph molts several times until it becomes a winged adult that can reproduce.

 

Complete Metamorphosis

Butterflies, beetles, and most other insects go through complete metamorphosis. Complete metamorphosis includes four distinct stages: egg, larva, pupa, and adult. For example, when a butterfly egg hatches, a segmented larva emerges. The larva commonly called caterpillar, looks far more like a worm then an adult butterfly. Unlike a worm, however, a caterpillar has three pairs of jointed and several pairs of fleshy legs. A caterpillar devours leaves, grows large, and molts several times. Because caterpillars need a lot of food to grow so rapidly, they can cause much damage to the plants upon which they feed.

Typically when a caterpillar’s growth is complete, it finds a sheltered spot and hangs upside down. Its body becomes shorter and thicker. Its exoskeleton splits down the back and falls off. The insect now enters an immobile stage called pupa. Inside the pupa larval tissues are breaking down, and groups of cells called imaginal disks are developing into the tissues of the adult. During this process the pupa is encased in a protective covering, called a cocoon in moths and a chrysalis in butterflies. When metamorphosis is complete, a sexually mature winged adult emerges.

Hormonal Control of Metamorphosis

The process of metamorphosis is controlled by the sequential control of genes. These genes cause the production of three hormones: brain hormone, molting hormone, and juvenile hormone. Brain hormone stimulates a gland in the thorax to release molting hormone. The effect of molting hormone depends on the amount of juvenile hormone in the blood. During larval development the amount of juvenile hormone is relatively high, and the release of molting hormone at this stage causes the larva to mold. However, as the insect gets older, the production of juvenile hormone decreases. When the level of juvenile hormone falls low enough, molting hormone triggers the change from larva to pupa. When juvenile hormone is no longer present, molting hormone starts the change from pupa to adult.

Importance of metamorphosis

Metamorphosis is another adaptation that contributes to the great success of insects. In a life cycle based on complete metamorphosis, different developmental stages of insect fulfill different functions. For example, a caterpillar is specialized for growth, while an adult butterfly is specialized for dispersal and reproduction. One of the advantages of this specialization is that it eliminates conflict between two activities that require great amounts of energy - growing and reproducing.

Metamorphosis also enhances insect survival in two other ways. First, it eliminates competition between larvae and adults for food and space. For example, a caterpillar eats leafy vegetation, but an adult butterfly feeds on flower nectar. Second, a multistage life cycle helps insects survive harsh weather. Most butterflies spend the winter encased as pupae. Likewise, the eggs of mosquitoes remain untouched through the winter. The larvae of nymphs of other insects spend the winter under water. Some are even protected from the cold by a chemical in the blood that is similar to the antifreeze used in car radiators.

4. List all the animals which are being used as examples in class.

Phylum Arthropoda

Subphylum Chelicerata

Class Merostomata - Horseshoe crabs

Class Arachnida - Spiders, ticks, mites, scorpions, daddy longlegs

Class Pycnogonida - Sea Spiders

Subphylum uniramia

Class Crustacea - Homarus, Cancer, Daphnia, Artemia, Cyclops, Balanus, Procellio

Class Chilopoda - Centipeds

Class Diploda - Millipeds

Class Insecta

Order

Number of Species

Examples

Orthoptera

("straight-wing")

23,000

Grasshoppers

Crickets

Katydids

Cockroaches

Isoptera

("equal-wing")

1,800

Termites

Dermaptera

("skin-wing)

1,100

Earwigs

Anoplura

("unarmed-tail")

200

sucking lice

Hemiptera

("half-wing")

40,000

All true bugs

Homoptera

("like-wing")

20,000

Aphids

Mealy bugs

Cicadas

Ephemeroptera

("for-a-day-wing")

1,500

Mayflies

Odonata

("toothed")

5,000

Dragonflies

Damselflies

Neuroptera

("nerve-wing")

4,600

Dobsonflies

Lacewings

Coleoptera

("sheath-wing")

280,000

Weevils

Ladybugs

Beetles

Lepidoptera

("scale-wing")

110,000

Butterflies

Moths

Diptera

("two-wing")

85,000

Mosquitoes

Flies

Gnats

Siphonaptera

("tube-wingless")

1,100

Fleas

Hymenoptera

("membrane-wing")

100,000

Bees

Wasps

Ants

5. Make a vocabulary list and briefly define them. Use all words printed in black.

1. Appendages - extensions of the body and include legs and antennae

2. Exoskeleton - hard external covering that provides support and protection

3. Chitin - a tough carbohydrate of which the exoskeleton of Arthropods is composed

4. Molting - the shedding of the exoskeleton so that the body can grow bigger and later a new skeleton can develop

5. Chelicerae - pincerlike mouthparts, present in members of subphylum Chelicerata

6. Mandibles - chewing mouthparts, present in Crustacea

7. Cephalothorax - consists of two the fused head and the thorax; has 13 segments and is covered by a hard carapace.

8. Abdomen - the final part of a crayfish, divided into seven segments

9. Telson - the seventh segment of the abdomen that forms a tail

10. Antennules - Appendages with receptors for touch, taste and equilibrium

11. Antennae - Specialized for touch and taste

12. Mandibles - Move up and down to crush food

13. Maxillae - Move side to side to tear food

14. Maxillipeds - "Jaws to hold food"

15. Chelipeds - Claws that capture food and serve as defensive weapons

16. Walking legs - Enable the crayfish to walk slowly

17. Swimmerets - Create water currents; function in reproduction

18. Uropods - Propel crayfish through water

19. Compound eyes - eyes with many lenses that are highly sensitive to light and detect motion well

20. Pedipalps - a pair of appendages attached to the cephalothorax that aid in chewing

21. Book lungs - paired sacs in the abdomen of arachnids with pagelike components, that provide a large surface area for exchange of gases.

22. Tracheae - tubes that carry air directly to the tissues

23. Malpighian tubules - hollow projections of the digestive tract in arachnids that collect body fluids, remove wastes, and carry wastes to the intestine.

24. Coxal glands - organs in some spiders that remove wastes and discharge them through an opening at the base of an leg

25. Spinnerets - tubes through which fluid used to make webs passes through and in which it hardens

26. Myriapods - centipedes and millipides called collectively

27. Structural variations - differences in structure of body such as mouthpart

28. Physiological variations - differences in the way internal systems work

29. Behavioral variations - differences in the ways insects respond to their surroundings.

30. Entomologists - scientists who study insects

31. Tarsus - Spines, hooks, and padson each grasshoppers foot

32. Labium and Labrum - liplike parts which the grasshopper uses to hold the grass in position so that the mandibles can tear off edible bits

33. Midgut - an insect’s stomach

34. Gastric ceca - pockets in grasshoppers stomach that secrete enzymes that digest food.

35. Hindgut - made up of coelom and rectum, where undigested matter from midgut travels

36. Aorta - a large vessel in grasshopper through which blood flows, often called grasshoppers hearth

37. Tympanum - a sound-sensing membrane

38. Ovipositors - pointed organs used to dig a nest hole in the soil and to deposit eggs

39. Metamorphosis - changes in both form and size as an insect develops

40. Nymph - immature form that looks somewhat like an adult but is maller

41. Pupa - an immobile stage of the complete metamorphosis

42. Cocoon( chrysalis in butterflies) - a covering protecting pupa

43. Camouflage - the ability to blend into surroundings used for defensive purposes in insects

44. Warning coloration - bold, bright colored patterns that are clearly recognizable and warn predators away.

45. Mullarian mimicry - several poisonous species having same warning coloration.

46. batesian mimicry - insects that are not dangerous or poisonous fool predators by having warning coloration of those who are.

47. Division of labor - the division of labor among different groups of insects living in a collective

48. Instinct - genetically controlled behavior

49. Royal jelly - a high protein substance which bees feed to the queen and to the youngest larvae

50. Pheromone - a chemical released by an animal that effects the behavior or development of other animals of the same species.

6. List the special adaptations which make this phylum successful on earth.

 

All members of the phylum Arthropoda share the following characteristics:

• arthropods have joined appendages. appendages are extensions of the body and include legs and antennae.

• the athropod body is segmented. a pair of appendages is attached to each segment. in some species the appendages have been lost or reduced in size during the course of evolution.

• arthropods have an exoskeleton. an exoskeleton is a hard external covering that provides protection and support.

• arthropods have a ventral nervous system, an open circulatory system, a digestive system, and specialized sensory receptors.

the name arthropod, meaning "jointed foot", refers to the jointed appendages. jointed appendages and an exoskeleton are the most distinctive arthropod traits. the exoskeleton provides much more structural support than the annelid cuticle and gives the internal organs better protection.

The chemical composition and the three-layered structure of the exoskeleton give it versatility and strength. The exoskeleton is composed primarily of protein and a tough carbohydrate called chitin. The waxy outer layer repels water and helps prevent desiccation in terrestrial species. The hard middle layer, which is strengthened by materials such as calcium, provides the primary protection. The inner layer, which is flexible at the joints, allows the animal to move freely. All three layers are secreted by an epidermis that lies just beneath them.

Unlike the muscles of annelids, which form continuous sheets in the body wall, the muscles of arthropods occur in bundles that attach to the inside of the exoskeleton on either side of the joints. By alternately contracting and relaxing these muscles, the arthropod in essence operates a system of levers that move the body parts and appendages.

Because the exoskeleton cannot enlarge as the body enlarges, the exoskeleton must be shed periodically and a new one must be formed. This process is called molting. Molting is also called ecdysis. The tissues of the arthropod grow until they put a great deal of pressure on the exoskeleton walls. A hormone is then produced that induces molting.

When an arthropod starts to molt, the cells of the epidermis secrete enzymes that digest the inner, flexible layer of the exoskeleton. Simultaneously the epidermis begins to synthesize a new exoskeleton, using much of the digested material. During this process the outer layer of the old exoskeleton loosens and breaks along specific lines. The old exoskeleton is then shed. The new exoskeleton, which is flexible at first, stretches to fit the now enlarged insect.

An arthropod molts many times during the course of its lifetime. Each time it molts, it becomes larger. However, during molting it is extremely vulnerable to predators because it temporarily lacks a hard shell. Terrestrial Arthropods are also susceptible to desiccation during molting. For these reasons, arthropods usually go into hiding when they molt until their new exoskeleton has hardened.

Many of the adaptations that have made insects successful are characteristics they share with other arthropods. For example, an exoskeleton, jointed appendages, and a segmented body are all common arthropod traits. However, insects are distinguished from other arthropods by the following arthropod traits: