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Arthropods
Characteristics
Arthropods-Insects
1. Makes up ¾’s of all
2.
3.
4.
5.
animals species
Includes insects, spiders,
scorpions, millipedes,
centipedes, crabs,
lobsters & crayfish
Anthropod means “jointed
foot/leg”
Jointed appendages (legs,
antenna, mouth parts)
Segmented body with
paired appendages on
each segment
Arthropods
• Millipedes
&
Centipedes
Arthropods-Spiders
6. External exoskeleton
made of chitin
(carbohydrate) & protein
for protection & support
7. Exoskeleton has 3 layersouter waxy layer repels
water, middle layer has
calcium for extra
strength & inner layer
has flexible joints for
movement
8. Deuterostomes
9. Coelomate
10. Ventral nervous system
Arthropods-Crabs & Barnacles
Arthropods-Scorpions
11. Open circulatory
system
12. Specialized sensory
receptors & high
degree of cephalization
13. Have simple or
compound eyes &
segmented antenna
Arthropods-Lobsters & Crayfish
Arthropods
Movement & growth
Arthropods-Horseshoe crabs
1. Muscles occur in
bundles & are
attached to inside of
exoskeleton on each
side of joints
Arthropod-Growth
2. Exoskeleton must be periodically molted (shed) for
organism to grow
3. Molting called ecdysis
4. Molting hormone released & causes epidermal cells to
secrete enzymes that digest & loosen inner
exoskeleton
5. New exoskeleton secreted by epidermal cells flexible at
first & must harden so arthropod not vulnerable to
predators so often stay in hiding after molting
6. Arthropods go through numerous molts
Arthropods
Evolution & Taxonomy
Arthropods
o Four subphyla
oTrilobita- extinct trilobites
oCrustacea- shrimps, lobsters, crayfish &
barnacles
o Chelicerata- spiders, scorpions & ticks
o Uniramia- centipedes, millipedes & insects
Arthropods
o Subphyla trilobita
o Includes extinct trilobite
o Marine
o Have a head & segmented trunk
with one pair of legs one each
segment
o Breathe through gills
o Single pair of antenna
Subphylum Chelicerata
• Characteristics
– 1.Includes 2 classes- Xiphosura (horseshoe crab)
and Arachnida (spiders, ticks, scorpions & mites)
– 2. Have a cephalothorax (fused head & thorax) and
abdomen
Subphylum Chelicerata
• Characteristics
8. Ticks & Mites
a. Parasitic arachnid
b. Need blood meal to molt
c. Ticks carry Lyme disease & Rocky Mountain
Spotted Fever
9. Scorpions
a. Prefer dry regions
b. Breath through book lungs
c. Nocturnal predators
Subphylum Crustacea
Characteristics
1.Marine members include shrimp, lobster, copepods,
barnacles & crabs
2. Terrestrial crustaceans called isopods includes
pillbugs & sowbugs
3. Freshwater members include crayfish &
Daphnia (water fleas)
4. All have jaws or mandibles for chewing or tearing
5. have 10 pairs of jointed appendages
6. Breathe through gills
7. Barnacles
a. Marine
b. Sessile crustaceans that live in limestone case
c. Filter plankton with 12 appendages called cirri
8. Isopods (pillbugs & sowbugs)
a. Some live on land in dark places
• 9. Crayfish
Subphylum Crustacea
a. Antennules located on head help balance, touch & taste
b. Statocysts- balancing organs at the base of antennules
c. Maxille- paired mouthparts that move side to side to tear
food
d. Maxillipeds- help hold food
e. Swimmerets- under abdomen to swim, gas exchange, &
protect eggs/ young
f. Abdomen ends in flat segment called telson with flat
uropods on each side
g. Chitinous teeth in stomach grind food
h. Open circulatory system with heart to pump blood to gills
& body cells
i. Gills attached to walking legs
Subphylum Crustacea
Copepods
a. Largest group of crustaceans
b. Make up most of the marine plankton
c. Serve as food for many marine
animals
d. Found in freshwater, marine & moist
terrestrial environments
Subphylum Uniramia
• Characterists
– 1.Includes 3 classes- Chilopoda (centipedes),
Diplopoda (millipedes) & Insecta
– 2. Most are terrestrial
– 3. Exoskeleton prevents desiccation (water loss)
• Class Chilopoda
– 1.Terrestrail centipedes – VS (not)
– 2. Have 1 pair of legs per body segment
• Class Diplopoda
– 1.Terrestrial millipedes
– 2. Roll into balls when threatened & spray
noxious chemical containing cyanide
Stop!
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The head and thorax are covered by a common “shell,” or covering
termed the “carapace.”
The front end of the carapace has “the rostrum,” a spike-like projection
from the front end.
The eyes are on stalks and there are two sets of sensory appendages
termed antennae.
Each of the first pair of antennae has two branches.
Each of the second pair of antennae has one long branch and a smaller
scale-like branch at the base.
The primitive forms have eight thoracic segments.
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Each thoracic segment bears an appendage that may be used for
walking.
Each thoracic appendage may bear a gill found up under and protected
by the carapace.
The abdomen projects beyond the carapace and has six segments.
The first five abdominal segments have flap-like swimming appendages
found underneath it.
The last abdominal segment bears a pair of lateral flaps and is typically
flattened. Together with the lateral flaps, it is often called the tail fan.
• Crabs are flattened
from top to bottom.
• The first pair of
remaining thoracic
appendages ends in
large pinching claws.
• The last four pairs of
thoracic appendages
are walking legs.
• The first abdominal
segment is small.
• The abdominal
appendages are small
and modified, and not
used for swimming.
• The abdomen is curved
under the thorax where
it fits in a groove on the
animal's underside.
True Crabs
Arthropods
of the PNW
Barnacles
Barnacles
• Acorn barnacle
• White acorn barnacle
• Leaf barnacle
True Crabs
• Dungeness crab
• (Shield-backed) Kelp crab
• Purple shore crab
True Crabs
• Red crab
• Oregon cancer crab
Other “Crabs”
• Hairy hermit crab
• Pacific mole crab
Shrimp
• Broken (Stiletto)back
shrimp
Isopods &
Amphipods
• Vosnesensky’s isopod
• Sand flea
Sea Spiders
• Stearns’ sea spider
Sea Spiders
Sea Spiders
Sea Spiders
Phylum Arthropoda
• Class: Merostomata--horeshoe crabs
• Class: Pycnogonida--sea spiders
• Class Crustacea:
(1)Subclass: Branchiopoda--fairy shrimp, brine
shrimp
(2) Subclass: Copepoda—copepods
(3) Subclass: Cirripedia—barnacles
(4) Subclass: Malacostaca:
• Order: Stomatopoda--mantis shrimp
• Order: Euphausiacea—krill
• Order: Decapoda--shrimps, lobsters, crabs
Stop