Download ARTHROPODA

Phylum
ARTHROPODA
Shari Bolar
Natalie Allcott
Brian Schuster
Bilateral Symmetry
Major Classes
•
•
•
•
•
Arachnida: spiders, scorpions, ticks, mites
Diplopoda: millipedes
Chilopoda: centipedes
Insecta: insects
Crustacea: crabs, lobsters, crayfish, shrimp,
barnacles
Orders of Insects
(a chosen few; there are many more)
Common Features of Arthropods
• Cuticle: the exoskeleton (external skeleton) that
is made of layers of protein and chitin, and
provides protection for the organism. Can be
thick or thin, provides attachments for muscles,
and is impermeable to water.
• Molting: shedding of cuticle in order to secrete
a larger one. Makes the arthropod vulnerable.
• Open circulatory system: hemolymph fluid
flows through open spaces (sinuses) which
surround organs and tissues. Important for
nutrient transport.
Common Features of Arthropods (cont.)
• Malpighian tubules: excretory organs that
remove waste from hemolymph in the circulatory
system
• Tracheal system: branched tubes with chitin
lining that carry O2 directly to cells (insects only)
• Spiracles: openings in exoskeleton that allow air
to enter tracheal system (insects only)
Unique Arthropod Features
• Book lung: respiratory organ of most spiders that
contains stacked plates in an internal chamber that
exchanges gases (mostly O2 and CO2) with a spider’s
body and the air
• Chelicerae: claw-like feeding appendages contained by
chelicerates (arachnids)
• Mandibles: jaw-like feeding apparatuses contained by
unimarians (centipedes, millipedes, insects) and
crustaceans
Unique Arthropod Features (cont.)
• Antennae: sensory organs that come in
pairs on the organism’s head
• Compound eyes: eyes with many parts and
multiple separate focusing elements
Life Cycle
Metamorphosis: a relatively abrupt change
in form or structure
Incomplete Metamorphosis
Young are similar to adults, but have
different body proportions and are smaller.
There are a series of molts that eventually
lead to the organism reaching full size.
Complete Metamorphosis
There are several distinct stages:
Larval stage specialized for
eating and growing
Pupal Stage actual change
occurs
Adult stage specialized for
reproduction
Germ Layers and Coelom
• triploblastic: have all three germ layers
(ectoderm, endoderm, an mesoderm)
• protostomes: the opening of the gastrula, the
blastopore, becomes the mouth and the second
opening becomes the anus
• start with a coelom during embryo development,
which becomes reduced over time.
• have open circulatory systems where
hemolymph fluid is propelled through sinuses.
These sinuses together are called the hemocoel.
As the coelom becomes reduced the hemocoel
becomes the main body cavity. Even though this
occurs they are still coelomates.
Reproduction
Reproduction is usually sexual with
differences in male and females. Potential
mates are advertised by bright colors, sound,
and odor. Fertilization is internal and is
done by normal intercourse. The female will
lay eggs. Mating normally happens only once
in a lifetime.
Camel Spider
(class Arachnida; order Solifugae)
It does not spin webs or have
book lungs. Many rumors
about the camel spiders’
speed, size and venom. In the
middle east, it was said that
these big, fast spiders would
come into your tent at night
and inject an anaesthetizing
venom that would put its
victims to sleep and feed on
victim leaving a gaping
wound. This is false, except
that they do leave a large bite
prone to infection.
Spider Feeding
Spiders use a fang like chelicerae equipped
with poison glands to kill prey caught in
web. Instead of fully chewing their prey, the
spider will spill digestive juices onto prey.
This softens the food and the spider will
suck up the liquid.
Review Questions
• What type of symmetry do arthropods have?
• Match the following classes with their members:
– Insecta
– Arachnida
– Diplopoda
– Crustacea
– Chilopoda
centipedes
crabs, lobsters, barnacles
insects
millipedes
spiders, scorpions
• In what stage of metamorphosis does abrupt
change occur?
• What do most spiders use to breathe?
• What process allows arthropods to shed their
cuticle in order to grow a larger one?
Review Questions
• Is fertilization internal or external?
• How are arthropods classified: protostomes or
deuterostomes?
• How many germ layers does a camel spider have?
• What do spiders use to feed on their prey?