Biology - Chapter 28 “Arthropods” Introduction to Arthropods l Phylum Arthropoda - vary enormously in size, shape, and habits

Biology - Chapter 28

“Arthropods”

Introduction to Arthropods

Phylum Arthropoda - vary enormously in size, shape, and habits

Crustaceans

Crustacea- over 35,000 species, mainly aquatic

tiny as a water flea (0.25 mm) to Japanese spider crabs (6 meter)

characterized by: a hard exoskeleton; 2 pairs of antennae; mouthparts called mandibles


Although there are many different types of arthropods, they all have four important arthropod features:

1. Tough exoskeleton – shed to allow for growth (molt)a. Protectionb. Prevent water lossc. Made up of chitin (protein)

2. Series of jointed appendages in pairs3. Segmented body – head, thorax, abdomen


4. Well developed nervous system-- sense organs – eyes, touch,

hearing– brain, located in dorsal part of

head– open circulatory system, powered

by a single heart• Flows into open cavities called

sinuses

Introduction to ArthropodsDevelopment through Metamorphosis:

1. Incomplete metamorphosis eggs hatch to nymph (kid) to adultexamples: grasshoppers and crickets

Spiders and their Relatives

–also lack sensory “feelers” found on the heads of most other arthropods

the two-part body is:1. Cephalothorax2. Abdomen

Introduction to Arthropods2. Complete

metamorphosis involves four stages:

a) the egg b) larvae (a wormlike stage

that does not look like the adults)

c) pupa (an inactive stage that totally rearranges the body)

d) the adultMoths, butterflies, flies, lady

bugs


Phylum Arthropods is subdivided into three subphyla:1. Subphylum Chelicerata–Includes spiders, ticks, mites, scorpions, and horseshoe crabs


Cephalothorax- contains the brain, eyes, mouth and mouthparts, and esophagusAbdomen- contains most of the internal organs


All chelicerates have two pairs of appendages attached near the mouth that are adapted as mouthparts–first pair are chelicerae–second pair is longer, and called pedipalps

both serve different feeding job


Among the oldest chelicerates are the horseshoe crabs


Scorpions- carnivores that prey on other invertebrates, usually insects–pedipalps are enormously enlarged into a pair of claws

–abdomen is long and segmented; ends in a venomous barb to sting prey

Introduction to Arthropods3 Subphylums

1. Subphylum Crustacea– includes crabs, shrimp, crayfish

Crustaceans

Main body parts are the head, thorax, and abdomenin many, the head and thorax have fused = cephalothorax, many (crabs, lobsters)


3. Subphylum Uniramia includes most arthropods: centipedes, millipedes, and all insects (bees, moths, flies, grasshoppers, beetles)

Insects Anatomy

Head –Antennae (sensory appendages)–Mouthparts–Compound eye

Thorax–3 pairs of legs–Wings?

Abdomen

Insects and their Relatives

Subphylum Uniramia- more species than all other groups of animals alive today!1. Class Insecta – flies, bees, butterflies, dragonflies, grasshoppers, lice, mosquitos

2. Class Chilopoda – centipedes3. Class Diploda -- millipedes

Section 28-2Spiders and their Relatives–Have 4 pairs of walking legs–long spike-like tails–can grow up to 60 cm long, about the size and shape of a frying pan

–newly hatched are called trilobite larvae because they look so much like them

Section 28-2Spiders and their Relatives

Class Arachnida- includes spiders, ticks, scorpions, and mites–have 4 pairs of walking legs–pedipalps capture and hold prey; chelicerae adapted for biting and sucking out soft parts


Spiders- predators that usually feed on insects

capture prey in a variety of ways:–ensnare in a web–stalk, and then pounce–ambush under camouflage, then leap out and grab


Once captured:1. Hollow fanglike chelicerae inject paralyzing venom

2. Mouth introduces enzymes3. Enzymes break down tissue4. Spider sucks up the liquefied tissues with esophagus and specialized pumping stomach


Whether or not they spin webs, all spiders produce a strong, flexible protein called silk–produced in special glands in the abdomen

–is 5 times stronger than steel–makes webs, cocoons for eggs, or wrappings for prey


Forces the liquid silk through organs called spinnerets–it then hardens into a single strand

–do not have to learn “how” to spin the intricate webs; it is programmed into their brain as soon as they hatch


Mites and Ticks- small arachnids, many of which are parasites–the chelicerae are needlelike structures that are used to pierce the skin of their hosts

–the chelicerae also have large teeth to help the parasite hold on to the host


Some, such as spider mites,are major agricultural pests

others, such as chiggers, mange and scabies mites,cause painful itching rashes in humans

tick bites are not just annoying; they may also spread Rocky Mountain spotted fever and Lyme disease


Scorpion grabs the prey with it’s pedipalps; then whips the abdomen over it’s head to sting the prey- thus killing or paralyzing it

they like to crawl in moist, dark places- good idea to check your shoes when putting them on!

Section 28-3Crustaceans

OBJECTIVES:–Discuss the distinguishing characteristics of crustaceans.


OBJECTIVES:–Describe the anatomy of a typical crustacean.


In crustaceans, the first two pairs of appendages are “feelers” called antennae, which bear many sensory hairs

third pair of appendages are mouthparts called mandibles–might bite and grind; filter feeding


Appendages can vary greatly–barnacles have delicate, feathery appendages for filter feeding

–others have legs for walking or swimming

–some modified for fertilization, carrying eggs, spearing prey


Appendages are adapted for:–the large claws catch prey; pick up, crush, and cut food- these are on the thorax

–4 pairs of walking legs, also on the thorax

–Flipper-like swimmerets for swimming on the abdomen


The paddle-like appendages and the final abdominal segment form a large, flat tail–very powerful; a crayfish can snap forward, thus rapidly pulling the animal backwards

“roly-poly” in Figure 28-22, page 620- pill bug (a crustacean)

Section 28-4Insects and their Relatives

OBJECTIVES:–Describe and give examples of three classes in the subphylum Uniramia.


OBJECTIVES:–Discuss the anatomy of a typical insect.


OBJECTIVES:–Explain how insects communicate.


They lack closable spiracles and a waterproof coating on their exoskeleton–thus they lose water easily–therefore, they tend to live beneath rocks, in soil, or in other relatively moist areas


Class Chilopoda- centipedesthese are carnivores that have in

addition to their mouthparts, a pair of poison claws in their head region–used to catch and stun or kill prey- other arthropods, earthworms, toads, small snakes, and even mice


Most centipedes in North America are 3-6 cm long; but some tropical species are brightly colored, and up to 26 cm

Despite the name (which means 100 legs), they can have a variable number, depending upon how long they are


There is only one pair of legs per body segment–except the mouth, which has the poison claws, and the last three segments (which are legless)


Class Diplopoda- these are the millipedes, and they do not have a thousand legs like the name implies–they have 2 pairs of legs per body segment

–these are timid creatures, and are detritus feeders


Class Insecta- the insects have more than 900,000 species; new ones are being discovered in the tropics all the time–3 out of every 4 animals!–three part body: head, thorax, and abdomen. There are 3 pairs of legs on the thorax


A typical insect has one pair of antennae, one pair of compound eyes on the head, two pairs of wings on the thorax, and uses a system of tracheal tubes for respiration

Figure 28-26, page 623


Insects get their name from the Latin word insectum, meaning notched- refers to the division of their body into the three parts–many insects, such as ants, have clear cut divisions- others such as grasshopper may not have body parts sharply defined


Feeding- insects have 3 pairs of appendages that are used as mouthparts, including a pair of mandibles (jaws)

many shapes and varieties:–grasshopper: cut / chew plants–mosquito: tube pierces skin to suck blood (females only)

Section 28-4Insects and their Relatives–butterfly: long tube for sipping nectar

–bee: chewing and gathering nectar

–fly: spongy mouthpart used to soak up food


The saliva of female mosquitoes, which is injected when the mosquito “bites”, contains chemicals that prevent blood from clotting- also has chemicals that cause the itching

bee body covered with many hairs that collect pollen


Chemicals in bee saliva help change nectar into a more digestible form- honey–glands on the bee abdomen secrete wax, which is used to build storage chambers for food and others structures within a beehive


Movement- insects have 3 pairs of walking legs–often equipped with spines or hooks for holding on, or used for defense

–may be used for jumping (fleas), or holding prey (praying mantis)


Movement- along with birds and bats, insects are the only living organisms capable of unassisted flight–flight ability varies greatly; from slow butterflies to fast flies, bees, and dragonflies

–requires enormous energy, thus have oversized mitochondria


Insect societies- many animals form colonies, collections of individuals of the same species–several types of insects for a special colony called a society

–separate individuals are dependent upon one another for survival


Insect societies- examples are termites, wasps, bees, and ants–all called social insects–they have a division of labor:1) reproductive females2) reproductive males3) workers


Reproductive females = queen, typically there is only one, and usually the largest individual in the colony- page 625–termite queen may be 14 cm long, 10 times normal

–can produce more than 30,000 eggs a day!


The reproductive males function only to fertilize the queen’s eggs–queen bee mates only once–the successful males die after mating, and the unsuccessful males are ejected from the colony and soon perish (since they are no longer needed!)


The workers perform all colony tasks except reproduction:–care for queen and eggs; gather and store food; build and maintain the colony’s home

–in bees, the workers are sterile females; in termites, the workers consist of males and females


Insect communication- may use sounds, visual, chemical, or other methods–may be necessary to find mate–male crickets chirp by rubbing their forewings together

–male cicadas buzz special membranes on their abdomen

Section 28-4Insects and their Relatives–Male fireflies turn a light producing organ in their abdomen on and off

many insects can release chemicals that attract the opposite sex- called pheromones

communication in non-social insects not near as complex


Queen bee produces a pheromone, called queen substance, that prevents the development of rival queens–this substance makes the worker bees unable to lay eggs

–need a new queen? Feed the larvae a special diet


Honeybees communicate with sound and movement, as well as with pheromones–worker bees are able to convey information about the type, quality, direction, and distance of food by “dancing”

Austrian biologist Karl von Frisch


1. Round dance- bee that has found food will circle first one way, then the other, over and over again (Fig. 28-32, p.627)–tells others that food is within 50 meters, but not direction

–frequency of dance conveys quality of the food


2. Waggle dance- the bee that has found food runs forward in a straight line while wiggling her abdomen, then circles around much like a figure eight–food is more then 50 m away–the direction of the dance tells the direction of the food source

Section 28-5 How Arthropods Fit Into the WorldOBJECTIVES:

–Describe how arthropods interact with other organisms in nature.

Section 28-5 How Arthropods Fit Into the WorldOBJECTIVES:

–Discuss how arthropods affect humans.

Section 28-5 How Arthropods Fit Into the WorldSuch a large diverse group will play many roles in the natural world–can be a direct source of food for many organisms

–either eating others or being eaten by them

Section 28-5 How Arthropods Fit Into the World

–Involved in symbiotic relationships Fig. 28-34, p.629

–pores of our skin are home to thousands of harmless microscopic mites; no matter how much we clean our home, even our beds, there are millions of these dust mites

Section 28-5 How Arthropods Fit Into the WorldAgriculture would be impossible

if not for bees, butterflies, wasps, moths, and flies that pollinate

honey from bees; silk from silkworm moths

shrimp, crab, crayfish, lobster used as a food source for humans

Section 28-5 How Arthropods Fit Into the WorldGrasshoppers and termites can also be eaten; they can also do considerable damage to crops and wood materials

many insects and spiders are predators on other harmful species

Section 28-5 How Arthropods Fit Into the WorldChemicals from arthropods

–extract of horseshoe crab blood is used to test purity of medications

–chitin from exoskeletons used to dress wounds and make thread for surgical stitches

Section 28-5 How Arthropods Fit Into the WorldThe chitin may also be sprayed

on fruit and frozen food to prevent spoilage

the adhesive that barnacles use to attach themselves to rocks under water could be used in dentistry or underwater construction

Section 28-5 How Arthropods Fit Into the WorldSpider venom is being tested as a pesticide

spider silk that could be used in making aircraft, helmets, bulletproof vests, and surgical thread

Section 28-5 How Arthropods Fit Into the WorldHowever good they are, they can

also do considerable damage:–parasites damage livestock and crops

–mosquitoes annoying bites and the spread of malaria and yellow fever

Section 28-5 How Arthropods Fit Into the WorldBiting flies carry diseases such

as sleeping sickness and river blindness

fleas carrying bubonic plaguetermites damaging woodlocusts (grasshoppers)

destroying crops

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Biology - Chapter 28 “Arthropods” Introduction to Arthropods l Phylum Arthropoda - vary enormously in size, shape, and habits