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
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
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
Exoskeleton- body covered with a hard
Why an exoskeleton?
Why not bones? Exoskeleton good for
small things, protects body from damage
(rainfall, falling, etc.).
Bones better for large things
Lobsters, crayfish, shrimp, and others
Free-floating larval stage
26,000+ known species
gills on legs, for example, in a lobster
Millipedes milli means thousand, pede
means legs, so ('thousand legged
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
Move rapidly, often found under logs; some in
have poison claws- modified 1st pair of legs
supposedly feels like a bee sting
Ticks, mites, and spiders
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
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
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
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.
Gradual change in appearance. For
example,wing pads grow longer with
each molt, and eventually into wings in
Immature forms are called NYMPHS
Generally have the same food source as
Immature is called a larva , with larva
perhaps having separate food source from
Larva and adult may have radically
different food sources, with very different
Example: Butterflies. Or, they may have
same food source: bees.
1. Direct harm
a. Annoyance-flies interfere with your
b. Venom-stings of scorpions and spiders
may even cause death.
c. Parasites-Fly larvae may cause myiasis,
Scabies and mange are caused by
2. Transmission of diseases:
a) Mechanical transmission.
b) Biological transmission. Pathogens spend a
part of their life cycle in the arthropods.
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.