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Invertebrates 2
There are more than 100,000 species of
 Most live in the ocean, but some can live
in freshwater, some even on land
 No matter what their shape or size, they
all have the same basic body plan
 Mollusks are soft bodied invertebrates
with a muscular foot and a mantle
Phylum Mollusks
Soft body
◦ Covered with a skinlike tissue called a mantle
 In many mollusks, the mantle produces a hard
Contain organs organized into systems
◦ Most organs in located in one area of their
body called a visceral mass
Muscular foot
◦ Used for movement
Characteristics of Mollusks
You can tell that snails are very different
from clams…
 And that both are different than an
 They are all examples of mollusks!
◦ They just belong to different classes within the
mollusk phylum
Diversity of Mollusks
Mollusks that glide along on a foot
underneath their bodies are called
◦ Ex. Snails, slugs
Most have one coiled shell, but not all
◦ Limpets have flattened cone shaped shells
◦ Slugs and nudibranches have no shell at all
Most eat plants and algae, some eat other
 As an adaptation for getting their food,
gastropods have a tongue-like organ
covered with rows of teeth called a
◦ Gastropods move their radula back and forth to
scrape off and scoop up food
Gastropods Eating
Gastropods that live in water have
respiratory organs called gills
◦ As water flows over the gills, oxygen is
Gastropods living on land have evolved a
cavity inside their bodies that serves as a
simple lung
Gastropods Breathing
The octopus and squid are the major
members of a second class of mollusks
called cephalopods
 In cephalopods, the foot is divided into
Mollusks with two shells hinged together
make up a third class called the bivalves
◦ Ex. Clams, oysters, mussels, and scallops
Have no head
Move very little, some remain attached to
one place
 Muscular foot
◦ Shaped and used differently than a gastropod
 Normally hidden inside the two shells
 Move by hooking the foot in sand then pulling
themselves along
Bivalves use gills to get oxygen
◦ They have a large surface area and a rich supply of
◦ Oxygen from the water passing over the gills
circulates into the blood
◦ Carbon dioxide, which is a waste product of
animals, is moved from the blood back into the
In some kinds of bivalves, water flows over
the gills when the shells are open
In clams, the water enters through a
muscular tube called a siphon
◦ After it flows over the gills, it leaves through
another siphon
Bivalves Breathing
Bivalves are filter feeders
 Cilia move water across the gills
 Tiny food particles, such as plankton, are
trapped by mucus on the gills
 Cilia then push the food into the animal’s
Bivalves Eating
Arthropod means “joint foot”
The largest of all animal phyla
About 85% of all animals are arthropods!!
More than a million different species
Some are so tiny you can barely see them
Some can grow to more than 4m across
Phylum Arthropoda
Jointed appendages
 Segmented body
◦ Head
 Has appendages used for sensing and feeding
◦ Thorax
 Holds legs for movement
◦ Abdomen
 Contains most organs
Characteristics of Arthropods
Arthropods are the only invertebrates with
jointed appendages
◦ Appendages are parts that extend from the
◦ Used for movement, defense, feeding, sensing,
and even reproduction
◦ A single arthropod may have a great variety of
appendages, each adapted for a particular use
Jointed Appendages
Arthropods’ bodies are covered by an outer
support structure called an exoskeleton
◦ Similar to a suit of armor worn by a medieval
◦ Waterproof and helps prevent the loss of body
◦ Provides support for the body
◦ Hard for protection but more flexible around the
Liquid secreted that hardens quickly to form
the exoskeleton
Some are thin and flexible
Others are very thick and rigid
The arthropod’s exoskeleton doesn’t grow
with its body
 When the body gets too big for its
exoskeleton, it goes through a process
called molting
Just before an arthropod molts, it makes a
new, thin, flexible exoskeleton under the old
The old exoskeleton splits along the top
surface and the animal crawls out
The arthropod swallows as much water and
air as it can to make itself as large as
possible and waits until the new armor has
◦ Very vulnerable and nearly defenseless as it is
Molting Process
Spiders, ticks, scorpions, and mites are all
 Two main body regions
◦ Cephalothorax: head and thorax fused
 Four pairs of legs attached
◦ Abdomen
◦ In ticks and mites, the cephalothorax and
abdomen are also fused together
Spiders produce a liquid form of silk in
glands and spin the silk into thread with
◦ When the liquid silk is exposed to air, it
becomes strong and solid
◦ Make different kinds of silk for catching prey,
making sacs for eggs, and anchoring webs
 Not all spiders spin webs, but all produce silk
Spider Silk
Spiders usually eat insects
 They catch them in their web
 Once trapped, the spider will inject a
poison into the insect that paralyzes it
 Next the spider injects its digestive
enzymes into the insect and sucks out its
insides that have become liquefied
Catching Prey
Oxygen goes into the spider’s blood
through book lungs
 Book lungs are made up of sheets of
tissue like the pages of a book
◦ It gives them a large surface area for gas
Spider Breathing
Although the word centipede means “100
legs” in Latin, most centipedes have about
30 legs
◦ Each body segment has one pair of legs
◦ Predators that eat insects, snails, slugs, &
◦ Have poison claws, antennas, mandibles, and
the ability to move very quickly
Millipedes are slow moving and eat plants
and decaying organic material
◦ More segments than centipedes, but still 2 legs
per segment
Centipedes and Millipedes
Crayfish, barnacles, crabs, shrimps,
lobsters, water fleas, pill bugs, and sow
bugs are all crustaceans
Have mandibles, which are jaw-like
appendages used for chewing and
crushing food
 Have 2 pairs of antennas that are used
for balance and sensing
◦ Other arthropods have one pair but no others
have two pairs
Have eyes that have multiple lenses called
compound eyes
◦ Very sensitive to light and movement
◦ Don’t produce a single image like human eyes
Characteristics of Crustaceans
Crayfish are typical crustaceans
 Large claws attached to their thorax to
grab food, protect itself, and walk
 Behind the claws are four pairs of walking
 Like all crustaceans, crayfish have
appendages on their abdomen
◦ For swimming
Most crustaceans move around freely, but
barnacles remain attached to one place
 Many barnacles produce hard, volcano
shaped shelters
◦ Inside this shelter is a crustacean with jointed
 Appendages used to paddle food into the
barnacle’s mouth when it is under water
Another class of arthropods are the
 More species of insects than any form of
life combined
Ability to adapt to many different habitats
◦ From high mountains to dry deserts to rivers
and wetlands to your backyard
Ability to fly
◦ Helps insects find food, escape predators,
locate mates, and reach new places to live
Flexible adaptability
◦ In the process of evolution, insect body parts
have been modified for different ways of living
◦ Changes in mouthparts allow different species
ability to eat different food
Insect Advantages
Three pairs of legs
Only arthropods that have wings
◦ Most but not all have them
Three body regions
◦ Head, thorax, abdomen
Insects have tiny openings called spiracles
in its thorax and abdomen for air to enter
and flow through tubes called trachea
◦ Oxygen diffuses from these tiny tubes into the body
Body Structure of Insects
All insects reproduce sexually
◦ In most species the eggs are fertilized inside
the female’s body by a male’s sperm
◦ Many insects lay their eggs on a food source so
the young can begin to eat right after they
Most insects don’t look exactly like their
parents when they hatch from their eggs
◦ As they grow, they undergo a process called
◦ During metamorphosis, a young organism
changes its appearance to become an adult
Insect Reproduction
Some insects, such as grasshoppers, go
through an incomplete metamorphosis
 This is a series of molts in which the
insect changes from an egg to a nymph to
an adult
◦ A nymph looks like a little adult, but it has no
wings and is not yet able to reproduce
Incomplete Metamorphosis
Most insects go through complete
metamorphosis, which involves a more
complete change of appearance
◦ Bees, wasps, flies, beetles, butterflies, and moths
all go through it
They change from eggs to larvae to pupae to
◦ In the larvae stage, the insect usually looks like a
◦ During the pupa stage, the insect does not eat or
move around
 In many species the pupa is surrounded by a cocoon
 The insect is changing rapidly, forming adult structures
◦ When metamorphosis is complete, an adult insect
Complete Metamorphosis
Most insects live on their own, but some
species live together in colonies
 They are called social insects
 Social insects include termites, most ants,
bees and some wasps
 The members of the colony have
specialized functions and a system of
communication that allows them to work
together smoothly
Social Insects
Honeybees are a common example of
social insects
◦ Some bees go out of the hive to collect flower
◦ Some turn sheets of wax into the combs for
honey to be stored
◦ Queen bees lay eggs
◦ Some (nurse bees) care for and feed the young
What the larva are fed determines their
◦ Larva fed honey and pollen develop into worker
bees (always female) or into males called drones
 The worker bees egg-laying structures become
modified as a stinger
◦ Larva fed “royal jelly” develop into queen bees that
have both egg-laying structures and stingers
 Queen bees are only produced when the hive starts to
become overcrowded
 The first larva that becomes a queen bee leaves the
hive to find the first drone to mate with and becomes
the new queen of the hive
◦ The worker bees kill all the other developing queen bees
◦ The old queen takes half the worker bees and start a new
Determining Roles
The male drones are produced when the
queen lays an unfertilized egg
 Drones do almost nothing in the colony
 Only one drone mates with the queen
 Toward the end of the summer, the
worker bees either kill or chase all of the
drones out of the hive
◦ They are no longer needed for the survival of
the community
How does oxygen reach an insect’s body
What is a social insect? Give an example and
explain why social behavior helps the group
What determines whether a female larva will
become a worker bee or a queen bee?
What is the difference between a larva and a
nymph? How is each different from an adult
Choose an insect that you are familiar with.
Write a paragraph describing its body
structure. Draw a picture and label its body
3 simple eyes, 2 compound eyes
Upper and lower lips
2 jaws that bite sideways instead of up and down
Pair of antennae that have tiny sensory hairs for
smell and touch
◦ 3 pairs of jointed legs
 First 4 used for walking, last 2 used for jumping
◦ 2 pairs of wings
◦ Spiracles on each side for breathing
◦ Tympanum (eardrums) on each side
◦ Females have an egg-laying device called an
ovipositor on the end of their abdomen that they
can dig a hole to lay their eggs in
Grasshopper External Anatomy
Brain is in the upper part of the head
◦ Connected with and receives messages from
the eyes
Two nerve cords pass around the
esophagus and join together underneath
to form another brain-like structure
 Ventral nerve cord
◦ Runs along the ventral side of the body to the
tail end
Grasshopper Nervous System
Crop: food stored here
Gizzard: food ground up
Stomach: digestive juices secreted where the
food is digested
Intestines: digested food is absorbed into the
blood stream
Rectum: undigested food is sent here where
water is reabsorbed into the blood stream
Anus: unused materials are eliminated here
Grasshopper Digestive System
Spiracles: breathing pores on outside of
Spiracles open into air tubes called trachea
that branch to all parts of the body
◦ Trachea is lined with a constant film of moisture
Some are connected to large air sacs in the
thorax and abdomen
◦ Muscles cause the body to contract and expand
with pumps air in and out of the air sacs
Body cells absorb oxygen directly from the
air tubes
Grasshopper Respiratory System
Males have testes that produce sperm
 Females
◦ Have ovaries that produce eggs
◦ Have ovipositor (egg-laying equipment) that
allows for digging a hole to lay fertilized eggs
Grasshopper Reproductive System