Transcript Arthropoda

Introduction to Arthropoda
• 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.
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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.
Evolution
• Probably evolved from
a Peripatus(栉蚕) - like
ancestor, which in turn
evolved from a
segmented worm
Characteristics of Arthropoda
Metamerism(体节性)
• Metamerism- body is segmented.
Exoskeleton and metamerism causes
molting
Exoskeleton(外骨骼)
• 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
• Bilateral Symmetry- body can be
divided into two identical halves
Jointed Appendages
• Jointed Appendages- each segment may
have one pair of appendages, such as:
• legs
• wings
• mouthparts
Open Circulatory System
• Open Circulatory System- blood washes
over organs and is not entirely closed by
blood vessels. Our system is a closed one
Ventral Nerve Cord
• Ventral Nerve Cord- one nerve cord,
similar to our spinal column
Classes of Medical Importance
SUBPHYLUM Crustacea
(Formerly a Class)甲壳纲
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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
Class Diplopoda
• 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
Class Chilopoda
Centipede蜈蚣
• 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
Class Arachnida
• 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
Class Insecta
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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!!
Class Insecta
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.
characteristics
• 3 body segmentshead, thorax
(chest), abdomen
(stomach area).
• Insect means in
(into) sect (cut).
Class Insecta
• 1 pair of antennae
Class Insecta
• Tracheal Respiratory System- composed
of tubes, with holes (spiracles) through
the body that admit air.
• So, they do not have lungs at all.
Class Insecta
• 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?!)
Class Insecta
• 3 pair of legs, 1pair to each of the 3
thoracic segments.
• Compound eyes, with facets (ommatidia
小眼).
Insect mouthparts
• 1. chewing (beetles, cockroaches).
• 2. piercing-sucking (mosquitoes, bugs).
• 3. lapping and sponging (flies).
Insect Growth Basics
• 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 metamorphosis , or a
change in form.
Types of Metamorphosis
• Partial metamorphosis (gradual,
incomplete)
• Complete metamorphosis *most
advanced*
Incomplete Metamorphosis
• 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.
Complete Metamorphosis
• 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.
Harmful effects of arthropods
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Direct harm
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a. Annoyance-flies interfere with your
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work and rest.
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b. Venom-stings of scorpions and spiders
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may even cause death.
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c.
Parasites-Fly larvae may cause
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myiasis, scabies and mange are caused
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by Sarcoptes scabiei.
Harmful effects of arthropods
• 2. Transmission of diseases:
• a.
Mechanical transmission.
• b.
Biological transmission. Pathogens spend
a part of their life cycle in the arthropods.
• a)
Propagative
• b)
Cyclopropagative
• c)
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.