Transcript The Arthropods:

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Blueprint for Success
Chapter 14 and 15
 Modified
segmentation –
body regions specialized for
specific functions
(tagmatization).
 Chitinous exoskeleton used
for support and protection
 Paired, jointed appendages
 Growth accompanied by
molting (ecdysis)
 Ventral
nervous system
 Reduced coelom
 Open circulatory system
where blood is released into
tissue spaces (hemocoel)
 Complete digestive tract
 Metamorphosis often present
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Successful in almost all habitats on the earth.
Most abundant animals – Several million species identified
o 30 to 50 million species may yet be undescribed
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Triploblastic, protostome development
Exhibit bilateral symmetry
Four aspects contribute to arthropod success.
o 1. Metamerism
o 2. Exoskeleton
o 3. The Hemocoel
o 4. Metamorphosis
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Segmentation, most evident externally
Each external segment bears a pair of
appendages
Body cavity not divided internally
Permits the specialization of regions of the
body for specific functions
Regional specialization = Tagmatization
o Body regions (tagmata) specialized for: feeding,
sensory perception, locomotion, visceral
functions.
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External, jointed skeleton which encloses arthropods
Provides support, protection, and prevents water loss
System of levers for muscle attachment and movement
Secreted by epidermal cells
o Epidermis covered by exoskeleton on outside
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Consists of two layers:
o 1. Epicuticle = outermost, waxy lipoprotein layer
o 2. Procuticle/Endocuticle = bulky inner layer made of chitin
 Hardening
of the
procuticle provides
armor-like protection
 Modifications of the
exoskeleton
o Formation of joints
o Sensory receptors
(bristles, lenses, etc)
o Gas exchange
 Must
be periodically
shed for growth
(ecdysis)
 Epicuticle
and Procuticle:
epicuticle
exocuticle
procuticle
endocuticle
epidermis
 Provides
an internal
cavity for the open
circulatory system of
arthropods
 Allows for the
exchange of nutrients,
wastes, and
(sometimes) gases
 Indirect
development,
a significant change in
physiology as the
immature form
becomes an adult
 Reduces competition
between adults and
immature stages
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Evolution of arthropods has resulted in an increasing
divergence of body forms, behaviors, and habitats between
immature and adult stages.
o Ex: Larval crabs feed on plankton, adult crabs prowl sandy bottoms
for live prey.
o Ex: Caterpillar feeds on leafy vegetables, adult butterfly feeds on
nectar from flowers.
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Examples:
o Crayfish, crabs, lobster, shrimp, barnacles and copepods.
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Two unique characteristics:
o 1. Two pairs of antennae
o 2. Biramous appendages
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Five classes of crustaceans and numerous orders
o Class Malacostraca**
o Class Maxillopoda**
o Class Branchiopoda
o Class Remipedia
o Class Cephalocarida
 “Soft
Shell”
 Largest class of crustaceans:
o crabs, lobsters, crayfish, shrimp, krill, isopods
 Body
divided into two regions
o 1. Cephalothorax (fusion of sensory/feeding and
locomotion tagmata)
o 2. Abdomen (a muscular tail)
Paired, biramous appendages in both body regions
 Appendages on Cephalothorax:
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o Pairs 1 and 2 – Antennae (TWO pairs!)
o Pairs 3 through 5 – Mouth appendages
• Mandible Pair (Chewing)
• Maxillae (Food handling)
o Pairs 6 through 8 – Maxillipeds
• Accessory sensory and food handling appendages
o Pairs 9 through 13 – Pereopods (Walking legs)
• Cheliped (Pincher-like)
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Appendages on Abdomen
o Pleopods (Swimmerets)
o Telson used
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Reproduction
All crustaceans are
dioecious
Mating occurs after molting
of the female
In females, developing eggs
attach to pleopods and are
brooded until hatached
In males, pleopods are
modified into claspers and
used for sperm transfer
Crayfish have direct
development
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Feeding
Predators, herbivores,
scavengers
Foregut includes an
enlarged stomach,
specialized for grinding
Midgut = “intestine”
Short hindgut ends in
anus and used for water
and salt regulation
Gas Exchange & Circulation
 Gills in gill chamber
o Between the carapace and
body wall
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Muscular Heart
Dorsal, anterior, and
posterior arteries empty
into sinuses of hemocoel
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Sensory & Regulation
Ventral nervous system
Compound eyes
Crayfish: Excretion organs
are called “green glands”
Other crustaceans:
maxillary glands
 Includes
Barnacles and
Copepods
 Copepods are most
abundant crustacean
o Marine and Freshwater
 Barnacles
are sessile
o Marine only
o Most monoecious
o Attach to various
substrates
o Some are parasitic