Chapter 36 Arthropods& Chapter 37 Insects

“The real rulers of the Earth”Sources used include textbook, (Holt Modern Biology) http://www.ucmp.berkeley.edu/arthropoda/arthropoda.htmlhttp://evolution.berkeley.edu/evolibrary/article/_0_0/arthropods_intro_01

Just how dominant are arthropods?

• More than 83% of all described animal species are arthropods.

• That's about 160 million insects for each person on Earth.

• Have evolved to fill a variety of ecological niches — from tiny internal parasite to giant bird-eating predator.

• Arthropods are a lot more than just delicious feasts and disgusting pests.

• What are the characteristics of an arthropod ?

                                                                                                                                                                 

5 Characteristics of all Arthropods

Bilateral symmetry

• High degree of Cephalization

• Variety of segmented appendages around the mouth

• Segmented antennae- sense environment

• Compound eyes- made of many individual light detectors, each with their own lens.

Segmented Body

• Each body segment tends to repeat the same suite of structures (ie, a pair of legs, a set of breathing

organs, & a set of nerves),

• sets of segments are grouped into a larger unit, such as the abdomen & cephalothorax.

Hard Exoskeleton

• Made of protein & Chitin (a polysaccharide)• Must molt many times as grows• Enzymes digest the layer of exoskeleton

inside soften & then shed. It takes a few days for the newly excreted exoskeleton to harden.

Jointed Legs

• How can an animal with a rigid body covering move its legs? a problem for arthropods: flexibility.

• All arthropods (arthro = joint, pod = foot) have jointed limbs.

• In most of the leg, the exoskeleton is hard, but at the joints it is softer and bendable, allowing movement in the same way that a suit of armor does.

• The limb can be controlled by contracting muscles connected to the exoskeleton on both sides of the joint.

Many pairs of limbs• ancestral arthropod had

many body segments with one pair of limbs on each segment.

• in modern arthropods,– some limbs have even been

lost completely as they evolved to be smaller and smaller, while others have evolved into new shapes. functions.

• Tagma-specialized segements

Systems in Arthropods• All- Open circulatory system• Respiration-

– gills (aquatic crustaceans) – tracheae – book lungs (spiders)

• Excretion- – Green glands (Crusteaceans) – Malpighian tubules(spiders)

• Many arthropods have wings.• The two major types of mouthparts are:

– mandibles, which are jawlike– chelicerae (singular, chelicera), which are pincerlike

The five major subphyla of the phylum Arthropoda.

Arthropods usually divided into 5 subphyla based on:– differences in

development – in the structure

of appendages, such as mouthparts.

Trilobites

• Extinct• Many body appendages with one pair of

appendages per segment• Trilobites, living in shallow seas, flourished as

swimmers, crawlers and burrowers for some 350 million years. They evolved rapidly into many beautiful, bizarre and, even by today's standards, futuristic forms.

• Fossil evidence of these extraordinary marine creatures are found on all continents, entrapped in the hardened sediments of Ancient Seas.

http://www.trilobite.com/

Subphylum Myriapoda

• Means”many feet”

• One pair of branched antennae

• Many body segments

• Includes class: – Diplopoda (millipedes)

• Up to 100 body segments• 2 pairs of legs on each segment

– Chilopoda (centipedes)• In tropical regions can reach 12 inches long• From 15 to 175 pairs of legs

Subphylum Crustacea• contains about 38,000 known species.

• Terrestrial & Marine• so diverse their single defining characteristic is having two pairs

of antennae. • Most also have:

– a pair of mandibles– a pair of appendages on each body segment– some branched appendages– 16 to 20 segments & – several tagmata

• Many have a free-swimming

larval stage called a nauplius.

http://copepodes.obs-banyuls.fr/images/NAUPLIUS.jpg

a. Terrestrial Crustaceans

• Sow bugs and pill bugs are terrestrial isopods.

• They lack adaptations for conserving water and live only in moist environments.

• They generally feed on decaying vegetation.

• Pill bugs roll into a ball when disturbed or threatened.

b. Aquatic Crustaceans (many species)

• Copepods -important part of the ocean’s plankton.

• In freshwater, much of the plankton are water fleas such as Daphnia species.

• Barnacles are sessile as adults.

– Free-swimming barnacle larvae attach to surfaces and develop a shell that encloses the body.

– Barnacles use their cirri (singular, cirrus) to sweep food.

www.divediscover.whoi.edu

www.microscopyu.com

www.ryanphotographic.com

More aquatic crustaceans

• Order Decapoda -means“10 feet”

• Decapods have five pairs of legs

• Crayfish, lobsters, crabs, and shrimp are decapods

• Respiration through gills• (see more about crayfish in detail at end of

chapter- know parts for dissection lab)

4. Subphylum Chelicerata• Defined by presence of chelicerae

– The first pair of appendages– Modified into pincer or fangs

• Class Arachnid- spiders, scorpions, mites, ticks

• Some important Parts : – Chelicerae ( in spiders = fangs to inject poison)

– Pedipalps (hold food)

– 8 simple eyes at anterior of cephalothorax (NOT compound eyes!)

– Spinnerets- 3 pairs on tip of abdomen, for making silk

– Book lungs- like folds in a book= lots of surface area for gas exchange (some spiders use Tracheae for respiration instead)

– Malpighian Tubes- excretory tubes collect wastes, liquids. The liquid is reabsorbed (to conserve water) & waste is nearly solid.

Spiders-A full facial view of any spider shows its killing ability.

• Two powerful chelicerae, protrude down • Each chelicera bears a hinged fang. • Both fangs have ducts that lead up to the venom

glands within the head.

• Spiders fall into two groups, each being classified upon how they strike their prey. – The fangs of Tarantulas are so hinged that they articulate in

a front-to-back motion allowing them to strike their prey from above.

– Most other spiders have fangs that are hinged laterally, providing a left-to-right strike.

www.microscopix.co.uk/spiders/fangs/index.htm

Spider Chelicerae

Fangs, Chelicerae of Zebra Jumping SpiderSalticus scenicus

www.microscopix.co.uk/spiders/fangs/index.htm

Fangs and Chelicerae of Tarantula SpiderlingBrachypelma smithi(Mexican Red-Knee Tarantula)

Anatomy of a spider

** Mites and ticks differ from spiders because they

have a fused cephalothorax and abdomen.

Life of a Spider

• Spiders feed on insects and other small animals. Many species are adapted to capture certain prey.

• Spiders rarely harm humans, but two species in the United States are dangerous:– the black widow– the brown recluse

• A male spider is usually smaller than the female. • Females lay eggs in a silken case.

5. Subphylum Hexapoda

• Class Insecta• By many standards- the most successful group of

animals on earth.

• Entomology- the study of insects & terrestrial arthropods.

• Body of an insect is divided into 3 tagmata: – Head– Thorax– Abdomen

“bugs”

• Because they dominate all terrestrial environments that support human life, insects are usually our most important competitors for food, fiber, and other natural resources.

See page 743 for common insect orders

• See Example organism: Grasshopper• Please note parts for dissection lab,

see p 745 text.

The crayfish- next 4 pages are notes for dissection lab

• an abundant freshwater crustacean that is structurally similar to lobsters, which are marine crustaceans.

• Crayfish, lobsters, crabs, and shrimp are decapods, or members of the order Decapoda. Decapoda means “10 feet.”

• Decapods have five pairs of legs that are used for locomotion.

External Structure• The crayfish’s body is divided into

– the cephalothorax, which is covered by the carapace and is divided into

• the head, which has five segments• the thorax, which has eight segments

– the abdomen, which is is divided into six segments

• A pair of appendages is attached to each segment of the crayfish. Several pairs have specialized functions.

• These appendages include:– Antennae– Antennules– Mandibles– Maxillae– Maxillipeds– Chelipeds– Walking legs– Swimmerets

Crayfish -Parts for lab

Excretion• Green glands assist in excretion of excess water that enters the body

by osmosis.

Digestion• Digestive gland near the stomach secretes enzymes for digestion.

Respiration • gills.

Circulation• open.

Nervous & Sensory Organs• Many small sensory hairs. (sense water vibrations & chemicals) Compound

eyes are set on two stalks.

Chapter 37 Insects• Entomologists classify insects into more than

25 orders based on characteristics such as:– structure of mouthparts– number of wings– type of development

Factors responsible for their success include:–ability to fly -exoskeleton

–jointed appendages -small size–large numbers offspring -short life span

Just how dominant are insects?

Comparison of 2 of the 5 groups of Arthropods

Insects as Food • http://www.cals.ncsu.edu/course/ent425/text01/index.html

• Insects were undoubtedly an important source of nutrition for our early human ancestors.  Even today, they are still collected and eaten by people of many cultures.  In Mexico, dried grasshoppers are sold in village markets.  High in protein and low in fat, they may be fried or ground into meal and mixed with flour to make tortillas.  Sago grubs, the larvae of a wood-boring beetle, are considered a delicacy in Papua New Guinea.  The islanders boil the larvae or roast them over an open fire.  Ants, bees, termites, caterpillars, water bugs, beetle larvae, flies, crickets, katydids, cicadas, and dragonfly nymphs are among a long list of edible insects that provide nutrition for the people of Australia, Africa, South America, the Middle East, and the Far East.  Indeed, Americans and other descendents of western European culture appear to be unique among peoples of the world in having such a strong cultural taboo against the use of insects as food.

• Silkworm pupae forhuman food inThailand

A Recipe for Maggot Crispies

• 1/4 cup margarine4 cups small marshmallows3 cups crispy cereal3 cups dry roasted maggots or mealwormsIn a saucepan, melt margarine and marshmallows. Remove from heat and stir in cereal and maggots. Spread mixture in a 9x13 greased pan and allow to cool.

Insect body –is divided into three tagmata:

1. Head -has mandibles and one pair of unbranched antennae.

2. Thorax -has three pairs of jointed legs and, in many species, one or two pairs of wings.

3. Abdomen -has 9 to 11 segments but neither wings nor legs in adults.

Insects and People• Insects negatively affect humans by:

– competing for food– transmitting diseases– destroying buildings & other manufactured products

• Insects benefit humans by:– serving as food for other animals– pollinating flowers– making valuable products such as honey– recycling nutrients in ecosystems

External Anatomy Grasshopper

Internal Anatomy Grasshopper

Grasshopper body- three tagmata:

– The head • mouthparts -labrum & labium are mouthparts that

function like upper and lower lips, respectively.

• a pair of unbranched antennae• pairs of simple and compound eyes.

– The thorax is composed of:

• Prothorax

• Mesothorax

• Metathorax

– The abdomen has upper and lower plates

Insect mouthparts

Circulation, Respiration, & Excretion

• Insects have an open circulatory system that transports nutrients through the body.

• Gas exchange occurs by means of air-filled tracheae that reach deep into the body.

• Malpighian tubules remove cellular wastes from the hemolymph while conserving water.

Nervous system• The grasshopper’s central nervous system consists of

a brain and a ventral nerve cord with ganglia located in each body segment.

• Nerves extend from the brain to sensory structures.• Insect sensory structures include :

– simple and compound eyes– sensory hairs on antennae and other body parts

– in some species, a sound-sensing tympanum

Reproduction

• Grasshoppers have separate sexes, – as do all insects.

• During mating, the male deposits sperm into the female’s seminal receptacle, where the eggs are fertilized internally.

• The last segment of the female’s abdomen forms the ovipositor, which she uses to lay fertilized eggs.

Most insects go through

metamorphosis.

• In incomplete metamorphosis, a nymph hatches from an egg and resembles the adult but has undeveloped reproductive organs and no wings. The nymph molts several times to become an adult.

• In complete metamorphosis, a wormlike larva called a caterpillar hatches from an egg and molts several times before becoming a pupa. The pupa molts to produce the adult, which resembles neither the larva nor the pupa.

Incomplete vs. Complete metamorphosis

Complete metamorphosis -allows larvae and adults of the same species to avoid competing

for space and food.-allows survival in periods of harsh weather or scant resources.

See writing assignment sheet