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Invertebrates are animals that have no backbone.
An arthropod is an invertebrate with
an exoskeleton, a segmented body,
and jointed legs.
Some arthropods – such as insects,
centipedes, and millipedes are thought
to have evolved from ancestors of
annelid worms. Other arthropods, such
as crustaceans, spiders, and trilobites
(which are extinct), are thought to have
evolved from ancient and distantly
related ancestors.
There are more than 1 million kinds of
arthropods on Earth.
An exoskeleton is a hard, outer covering.
Exoskeleton
- Made of Chitin
- May be Flexible or very hard
- Usually waterproof in terrestrial arthropods
- Serves as protection
- Cannot grow as the arthropod grows
Molting is to leave an exoskeleton and
grow a new one.
Segmented Bodies
 Some arthropods have appendages on
every segment
 Other arthropods have lost segments
as they have fused together; some
appendages are lost as a result.
Jointed Appendages
 Antennae
 Claws
 Walking legs
 Wings
 Flippers
Etc.
They also have…
 A brain (in dorsal portion of head)
 A ventral nerve cord
 An Open Circulatory system
Internal Transport:
 They have an open circulatory system
– the heart contracts; blood is
pumped through arteries to vessels,
and then enters sinuses in the tissue.
Respiration:
 The three basic respiratory structures found in
arthropods are:
1. Gills: movement of mouthparts and appendages
keep water moving over gills; most look like a
row of feathers under the exoskeleton
2. Book gills and book lungs: Layered sheets of
tissue increases surface area (SA) for gas
exchange; in spiders, spiracles connect book
lungs with outside air
3. Tracheal Tubes: lead from spiracles into tissues
of the arthropod; movements of body cause
tracheal tubes to expand and contract, moving
air in and out through the spiracles.
Response:
 Arthropods have a well-developed nervous system:
 Brain with a pair of ganglia
 Pair of nerves connect brain to ventral nerve cord
 Ganglia along the length of the ventral nerve cord (coordinate
movement of legs and wings)
 Statocysts (involved in balance)
 Chemical receptors
- crustaceans and insects have a well-developed sense of
taste
- chemical receptors are found in mouthparts, antennae and
legs
Response continued:
 Most arthropods have compound eyes (which detect
color and motion very well)
 Crustaceans and insects have sensory hairs that
detect movement (of water or air)
 Most insects have well developed ears/hearing
(oval tympanum)
Excretion:
 Terrestrial arthropods:
 Malpighian tubules remove nitrogenous wastes from
blood, concentrates the wastes, and adds them to
solid wastes prior to elimination (through the anus);
some also have excretory glands at the bases of legs
 Aquatic arthropods:
 Metabolic wastes diffuse out of the body at the gills;
some have a gland called a green gland (in the head)
that empties metabolic wastes out of the body
Reproduction:
 Arthropods reproduce sexually
 Internal fertilization (within the female)
 Spiders and some crustaceans: male deposits a
sperm packet that the female picks up
 Most insects and crustaceans: males deposit sperm
inside the female via a specialized reproductive
organ
Movement:
 Muscle systems coordinated by the
nervous system
 Muscles allow the movement of
appendages by generating a force
agains the exoskeleton


Subphylum Trilobita – all forms believed to be
extinct – could be some of the earliest arthropods
Subphylum Chelicerata – First pair of
appendages form ‘Chelicera’ or pincher-like
structures used for feeding.

4 pairs of walking legs, no antennae. The ‘Arachnida’
is the only important parasitic group.


Subphylum Crustacea = mostly aquatic, most
have gills, two pair of antennae. Biramous
appendages, meaning limbs have more than one
branch. Also have mandibles. Some are
parasitic, but we will not cover them.
Subphylum Uriramia – single branch or
‘Uriramous’ appendages, mandibles, one pair of
anntennae.



Diplopoda – Millipedes – two pairs of legs per
body segment
Chilopoda – Centipedes – one pair of legs per
body segment
Insecta – 3 pairs of legs on adults, many with
wings.

Most important group.
A crustacean is an arthropod that has a hard
exoskeleton, two pairs of antennae, and a
mouth for crunching and grinding.
Crustaceans can ________ certain parts
of their body.
A ___________ can re-grow its claws.
Most crustaceans live in ______ and get
oxygen from the water through _________.
Gills are
Crustaceans live in a wide range of
habitats, from marine, to fresh
water, and even terrestrial – they
were the first animals to colonize
land.
* Centipedes and millipedes are arthropods
that have many legs.
* Have _______ pair of legs in each segment.
* Are carnivores and eat _________.
* To capture its prey, a centipede puts
_______ into the prey’s body with its_______.
* Centipedes are found in ___________ like
under rocks and in the soil.
* Have ___ pairs of legs on each segment.
* Eat _________ and are shy animals.
* When scared, it _________________ to protect
itself.
* Do not have ________.
* Are found in __________like under rocks and in
the soil.
* All have __________ legs.
* Have a body divided into two parts:
•______________________________
•________________________________
* Spiders usually eat __________, but some spiders
eat small _______________ like hummingbirds.
* Many spiders make webs out of _________.
* Silk is _________________________________.
* Spiders catch their prey in many different ways.
* Some spiders catch their prey in ____.
* Some spiders ________ from their prey
and then ________________.
* When spiders catch their prey, they _______ it
and _________ it.
* Spiders breathe oxygen with __________.
* Scorpions usually live in __________ areas.
* Most scorpions are __________________.
** Nocturnal means ____________________
* During the day, scorpions hide __________
______________________________.
* When scorpions capture prey, they _______
___________________________________.
* Ticks and mites live on _______________.
* Some ticks and mites suck juices from
____________________.
* Other ticks and mites are very tiny and live
on __________.
* Many ticks suck the blood from _________.
* Ticks can spread ________.
*There are more kinds of insects than there
are all other animal species all together.
* There could be _______________ times as
many insects as humans on Earth.
* Insects have a body that is divided into ____ parts.
* An insect’s body is divided into a ________,
a _____________, and a ___________ area.
* Insects have _____ legs connected to the chest part.
* Some insects’ legs are all the same size. Some
insects have one pair of legs larger than the other
two pairs.
* A grasshopper has one pair of legs larger than the
other two pairs. These larger legs are used for
____________.
Longer back legs
* Insects eat a lot, so they grow very fast. As they
grow, insects may molt and grow new ___________,
or they may change completely.
* A huge change in appearance is called ________.
* There are two kinds of metamorphosis:
______________ and ______________.
* In complete metamorphosis, insects like
butterflies and moths have _______ stages of
development.
* The first stage makes an ________.
* During the second stage, the egg hatches and a
_________ comes out.
* A caterpillar is the larva of an insect that will
become a butterfly or a moth.
* During the third stage, a ___________ is made.
* A pupa is sometimes wrapped in a
_____________ or in a _______________.
* A cocoon is the pupa of a _____________.
* A cocoon is made of ________.
* A chrysalis is the pupa of a ___________.
* In the last stage, the insect is finally an adult.
* Incomplete metamorphosis happens in
grasshoppers, termites, and dragonflies.
* In incomplete metamorphosis, young animals that
look like the ___________ hatch from eggs.
* As the young animals grow, they keep _________,
shedding their exoskeletons, and getting larger.
Metamorphosis
Simple or gradual
-Three Changes
- Egg
- Nymph
- 3 – 5 instars
- Adult
- Adults and nymphs eat the same food.
* Most insects live alone. But, some insects
are ___________ and cannot survive alone.
* These insects live in ______________ or hives.
* A colony is _____________________________
_______________________________________
* An amazing example of a colony is a __________.
* A beehive is ___________________________.
* All insects must protect themselves.
* Bees and wasps have _______________ to
protect themselves.
* Many other insects use ______________.
* Camouflage allows an insect to hide by ___
_______________________________.