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.html
http://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.
www.divediscover.whoi.edu
• Barnacles are sessile as adults.
– Free-swimming barnacle larvae attach to
surfaces and develop a shell that encloses
the body.
www.microscopyu.com
– Barnacles use their cirri (singular, cirrus) to
sweep food.
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 and Chelicerae of
Tarantula Spiderling
Brachypelma smithi
(Mexican Red-Knee Tarantula)
Fangs, Chelicerae of Zebra Jumping Spider
Salticus scenicus
www.microscopix.co.uk/spiders/fangs/index.htm
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
–jointed appendages
–large numbers offspring
-exoskeleton
-small size
-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 for
human food in
Thailand
A Recipe for Maggot Crispies
• 1/4 cup margarine
4 cups small marshmallows
3 cups crispy cereal
3 cups dry roasted maggots or mealworms
In 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
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