Download Phylum Arthropoda

Phylum Arthropoda
Crayfish, Lobsters, Spiders, Mites,
Scorpions, & Insects
Characteristics of the Phylum
Arthropoda
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Largest Phylum in the Animal Kingdom
Metameric – dividing the body into sections
 Tagmatization – each section is based on
function
Exoskeleton made of chitin
Paired, jointed appendages
Many go through a molting period called
ecdysis
Open circulatory system
Many go through at least one larval stage
Advantages & Disadvantages of
Having an Exoskeletons
Advantages:
 Prevention of water loss
 Provides a system of levers for muscle attachment
and movement
 Provides protection
Disadvantages:
Cannot grow with the arthropod, so must be shed, or
molted, in a process called ecdysis.
Molting can take a few hours or a couple days and
leaves the animal very vulnerable to predators and the
environment. This is why many arthropods will hide
during this process.
Metamorphosis
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Changing from a larval form to an adult
form.
Caterpillar to butterfly
 Maggot to fly
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What is the purpose of having two (or
more) separate stages of development?
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Means that the stages do not compete with
one another for food or living space.
Metamorphosis Types
1) Incomplete – egg, nymph, adult
 Egg hatches into a nymph which is a smaller,
wingless form of the adult. After wings
emerge, it is considered an adult.
 2) Complete – egg, larva, pupa, adult
 Egg hatches into a larva whose job it is to eat
voraciously. The larva spins a chrysalis, pupa
or cocoon. After enzymes and hormones
produce a body change, an adult emerges.
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Complete Metamorphosis
From Raven/Johnson, Biology, 3rd ed., Copyright © 1999 The McGraw-Hill Companies.
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Incomplete Metamorphosis
From Hickman/Roberts/Larson, Integrated Principles of Zoology, 11th ed., Copyright © 2001 The McGraw-Hill
Companies.
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The Earliest Arthropod
Trilobites – similar to today’s wood louse (rolypoly) just MUCH bigger
 Trilobites went extinct about 345 million years
ago, during the time of the dinosaurs.
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SubPhylum Chelicerata
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Spiders, Mites, Ticks, Horseshoe
Crabs, Sea Spiders, Water
Scorpions, & Scorpions
Usually have 2 tagmata
 The head tagma (cephalothorax)
is used for sensory, feeding, and
locomotion. Usually has eyes,
but no antennae; instead, it has
chelicerae and pedipalps.
Behind the pedipalps are 4 pairs
of walking legs.
 Chelicerae are usually pincers or
fangs used in feeding. Pedipalps
are usually sensory, but can also
be used for feeding, locomotion,
or reproduction.
 The tail tagma (opisthosoma)
contains the digestive,
reproductive, excretory, and
respiratory organs.
Class Merostomata – Horseshoe
Crabs
Horseshoe Crabs – have remained virtually
unchanged for over 200 million years. Only 4
species remains in existence today.
 Use book gills to exchange gases between the
water and their blood. Called book lungs
because they look like the pages of a closed
book.
 Horseshoe crabs are dioecious. The female
digs a hole in the sand to lay her eggs and the
male then fertilizes them. Fertilized eggs are
covered with sand and develop unattended.
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Horseshoe Crab Ventral View
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Class Arachnida – spiders, mites,
ticks, and scorpions
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Dioecious
Most arachnids are carnivores. Some hold their food
with their chelicerae while enzymes from the gut tract
pour over the prey. Partially digested food is then
taken into the mouth. Others inject the enzyme
directly into the prey through hollow fangs.
The excretory system of arachnids is made of either
coxal glands or Malpighian tubules that excrete uric
acid.
Some arachnids exchange gases using book lungs,
others use tracheae, similar to our lungs, where
oxygen enters through openings called spiracles.
Malpighian Tubules, Spiracles, &
Tracheae
Order Aranaea - arachnids
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The chelicerae are fanglike
and bear poison glands;
while pedipalps are leglike
and adapted for sperm
transfer in males.
Have 6 to eight eyes.
Have spinnerets that produce
silk for webs. Some spiders
even use their silk to help the
move from one location to
another, just like Spiderman.
All spiders are poisonous to
something, but most aren’t
poisonous to humans. Black
widows and brown recluse
spiders are the exception!
Brown Recluse Bite
Order Opiliones – Daddy Long Legs
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These guys are NOT
spiders, therefore
they do not have
poisonous
chelicerae.
Therefore, the rumor
that daddy long legs
are poisonous is
COMPLETELY
FALSE!
Order Acarina – mites and ticks
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Many are parasites.
Mite example – scabies.
A female scabies mite
can tunnel into human
skin where it will lay
about 20 eggs a day.
This causes intense
itching and can be
acquired by contact with
an infected individual.
Ticks – Feed on blood
and can cause several
diseases, including
Lyme disease.
Dermatophagoides
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Dust mite
 Feeds on
microscopic food
particles in dust.
 Allergies to fecal
products
 1 gram of dust holds
250,000 droppings
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Order Scorpionida (Scorpions)
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Common in hot, dry climates.
Nocturnal; during the day,
they hide under logs and
stones.
Have fanged chelicerae and
modified pincher pedipalps.
Only a few species have
venom that is toxic to
humans, most scorpion stings
are equivalent to wasp stings.
Scorpion mothers provide
care to their young by
allowing them to crawl onto
her back and remain there for
up to a month after birth.
Class Crustacea
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Includes crabs, lobsters,
crayfish, brine shrimp, shrimp,
water fleas, barnacles, & wood
lice (roly-polys).
Most are marine, but some live
in freshwater or on land.
Dioecious
Have 2 pairs of antennae.
5 pairs of legs (4 for walking, 1
for grasping); the claws are
called chelipeds
Breathe using gills.
Many have compound eyes (an
eye with more than one lens).
The top shell is called the
carapace.
Class Diplopoda: Millipedes
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Have 11 to 100
segments, not 1,000.
Each segment has 2
pairs of legs.
 Round in shape.
 Herbivores
 Almost always found
under decaying leaves
or logs.
 Can excrete cyanide
when threatened or
attacked.
Class Chilopoda: Centipedes
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Have 15 or more
segments. Each
segment has only one
pair of legs.
 Most are nocturnal.
 Predators; have poison
claws for immobilizing
prey; however most
centipedes are NOT
poisonous to humans.
 Flattened body.
Class Hexapoda - Insects
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Single largest class of all
animals.
Includes bees, flies,
grasshoppers, lice,
butterflies, moths, ants, and
beetles.
Has 3 body regions, head,
thorax, & abdomen.
3 pairs of legs attached to the
thorax.
Many have wings and 1 pair
of antennae.
Have grinding and shearing
mouth parts called the
mandible and the maxilla.
Insect Flight
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Insects were the first animals to fly.
 Wings have thickened, hollow veins for
increased strength.
 Most insects have to reach an internal
temperature of about 80 degrees Fahrenheit
for their muscles to contract rapidly enough to
for flight.
 Frequencies of up to 1,000 wing beats per
second have been recorded in midges!