 The arthropods are by far the most
successful phylum of animals, both in
diversity of distribution and in numbers of
species and individuals.They have adapted
successfully to life in water, on land and in the
air.

 About 80% of all known animal species
belong to the Arthropoda - about 800,000
species have been described, and recent
estimates put the total number of species
in the phylum at about 6 million.

 Arthropods are found in a greater variety
of habitats than any other animal group; on
top of mountains, at great depths in the
ocean and in the icy wilderness of
Antarctica.They can survive great
extremes of temperature, toxicity, acidity
and salinity.

 Probably evolved fromProbably evolved from
a Peripatus - likea Peripatus - like
ancestor, which in turnancestor, which in turn
evolved from aevolved from a
segmented wormsegmented worm

 Metamerism- body is segmented.
Exoskeleton and metamerism causes
molting

 Exoskeleton- body covered with a hard
external skeleton
 Why an exoskeleton?
 Why not bones? Exoskeleton good for
small things, protects body from damage
(rainfall, falling, etc.).
 Bones better for large things

 Bilateral Symmetry- body can be divided
into two identical halves

 Jointed Appendages- each segment may
have one pair of appendages, such as:
 legs
 wings
 mouthparts

 Open Circulatory System- blood washes
over organs and is not entirely closed by
blood vessels. Our system is a closed
one

 Ventral Nerve Cord- one nerve cord, similar
to our spinal column

 Lobsters, crayfish, shrimp, and others
 Primarily aquatic
 Free-floating larval stage
 26,000+ known species
 Branched appendages:
 gills on legs, for example, in a lobster

 Millipedes milli means thousand, pede
means legs, so ('thousand legged
creature'?)
 Most feed on decaying matter
 Diplo means two, poda means feet, so two
pair of legs per segment
 Generally harmless detritus feeders
 pests in nursing homes.
 Some species can eject cyanide (poison), so
be careful if traveling to South America

 Centi means hundred, pede means legs, so
"hundred legged creature"?
 1 pair of legs per segment
 Usually shiny, reddish brown, less than 3 inches
long
 Move rapidly, often found under logs; some in
homes
 Can bite
 have poison claws- modified 1st pair of legs
 supposedly feels like a bee sting

 Ticks, mites, and spiders
 No antennae
 Two body regions: cephalothorax and abdomen
 Feeding appendages are chelicerae Most are carnivorous
 They hold the prey with chelicerae, and pour enzyme-rich
salivary juices over the victim
 Digestion is mostly external
 Most are terrestrial
 57,000 known species

The insects are the most numerous
and diverse of all the groups of
arthropods.There are more
species of insects than species in
all the other classes of animals
combined!!

Insects differ from other
arthropods in having three pairs of
legs. In size, insects range from
less than 1 mm to 20 cm in length,
the majority being less than 2.5 cm
long.

3 body
segments-
head, thorax
(chest),
abdomen
(stomach area).
 Insect means in

 1 pair of antennae

 Tracheal Respiratory System- composed of
tubes, with holes (spiracles) through the
body that admit air.
 So, they do not have lungs at all.

 Wings- usually two pairs of wings,
although some have one pair of wings, or
none. No other class of arthropods has
wings. (Have you ever seen a flying
Lobster?!)

 3 pair of legs, 1pair to each of the 3 thoracic
segments.
 Compound eyes, with facets(ommatidia).

1. chewing (beetles, cockroaches).
2. piercing-sucking (mosquitoes,
bugs).
3. lapping and sponging (flies).

 Insects develop from egg. Eggs come in a
variety of shapes and sizes.
 They hatch from the egg, and begin eating
 Sooner or later they become too big for
their exoskeletons.
 They Molt , or shed their skins. Molting is
the shedding of old cuticle and expanding
into a new and larger one.
 Changes in the insect may occur with each
molt.This is called metamorphosismetamorphosis , or a
change in form.

Partial metamorphosis (gradual,
incomplete)
Complete metamorphosis * most
advanced*

 Gradual change in appearance. For
example,wing pads grow longer with
each molt, and eventually into wings in
the adult.
 Immature forms are called NYMPHS
 Generally have the same food source as
the adult.

 Immature is called a larva , with larva
perhaps having separate food source from
the adult.
 Larva and adult may have radically
different food sources, with very different
environments.
 Example: Butterflies. Or, they may have
same food source: bees.

1. Direct harm
a. Annoyance-flies interfere with your
work
and rest.
b. Venom-stings of scorpions and spiders
may even cause death.
c. Parasites-Fly larvae may cause myiasis,
Scabies and mange are caused by
Sarcoptes scabiei.

2. Transmission of diseases:
a) Mechanical transmission.
b) Biological transmission. Pathogens spend a
part of their life cycle in the arthropods.
i. Cyclopropagative
ii. Cyclodevelopmental
c) Transovarian.

 b) Cyclopropagative -The pathogenic
organisms undergo a developmental cycle in the
arthropod with multiplication and change in form.
Plasmodium sp. In anopheline mosquitoes.
 c) Cyclodevelopmental -The pathogenic
organisms undergo a change in form without
multiplication. Filaria in mosquitoes.