Download How do Arthropods maintain homeostasis?

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Introduction to Arthropoda
 The arthropods are 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.
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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.
Evolution :
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Probably evolved from a Peripatus - like ancestor, which in turn evolved from a
segmented worm
Metamerism
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Metamerism- body is segmented. Exoskeleton and metamerism causes molting
Exoskeleto
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Exoskeleton- body covered with a hard external skeleton
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Why an exoskeleton?
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Why not bones? Exoskeleton good for small things, protects body from damage
(rainfall, falling, etc.).
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Bones better for large things
Bilateral Symmetry :
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Bilateral Symmetry- body can be divided into two identical halves
Jointed Appendages :
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Jointed Appendages- each segment may have one pair of appendages, such as:
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legs , wings , mouthparts
Open Circulatory System :
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Open Circulatory System- blood washes over organs and is not entirely closed by
blood vessels. Our system is a closed one
Ventral Nerve Cord :
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one nerve cord, similar to our spinal column
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Closed Circulatory System
Open Circulatory System
Classification :
1-Subphylum Trilobitomorpha
2-Subphylum Cheliceriformes
Class Chelicerata
Subclass Merostomata (horseshoe crabs)
3- Subclass Arachnida (spiders, scorpions, mites, ticks)
Class Pycnogonida (sea spiders)
4-Subphylum Myriapoda
Class Chilapoda (centipedes)
5-Subphylum Hexapoda
Class Insecta
6-Subphylum Crustacea :
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a heterogeneous taxon with many subtaxa
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two pairs antennae
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marine, freshwater, and terrestrial
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Primarily aquatic
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Free-floating larval stage
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26,000+ known species
 Class Branchipoda (brine shrimp)
 Class Maxillopoda / Subclass Copepoda
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Class Malacostraca
Order Decapoda (crabs, lobsters, shrimp)
 Class Malacostraca
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Order Decapoda
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Order Isopoda (isopods)
Phylum Arthropoda
1-Subphylum Trilobitomorpha
2-Subphylum Cheliceriformes
A- Class Chelicerata
Subclass Merostomata (horseshoe crabs)
B- Subclass Arachnida (spiders, scorpions,
mites, ticks)
Class Pycnogonida (sea spiders)
5-Subphylum Crustacea
A- Class Branchipoda (brine shrimp)
B- Class Maxillopoda
Subclass Copepoda (copepod)
C-Class Maxillopoda
Subclass Copepoda (copepod)
D-Class Malacostraca
Order Decapoda
(crabs, lobsters, shrimp)
3-Subphylum Myriapoda
Class Chilapoda (centipedes)
E- Class Malacostraca
Order Decapoda
Order Isopoda (isopods)
4-Subphylum Hexapoda
Class Insecta
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Arthropods support and movement
Cuticle :
 Secreted by epidermi
 Waxes, lipoproteins, proteins.
 Sclerotized - tanning process that hardens
 Each segment bound by four plates - dorsal tergite, ventral sternite, and two lateral
pleurites.
 Muscle bands attach to apodemes.
 Appendages segmented with extrinsic or intrinsic muscles.
How do Arthropods support themselves and move?
Cuticle
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NERVOUS SYSTEM
Side view of body showing
relative position of circulatory
(yellow), digestive (green), and
nervous (blue) systems.
NERVOUS SYSTEM
General
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nervous system is adapted for the needs of a segmented animal as is that of annelids
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annelid and arthropod nervous systems are similar
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the similarities may be convergent
2. Arthropod Ground Plan
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ladder like nervous system
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dorsal brain in the head
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a pair of circumenteric connectives that encircle the gut
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a paired, ventral, longitudinal nerve cord
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paired segmental ganglia
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transverse commissures between ganglia
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longitudinal connectives
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segmental sensory and motor nerves
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SENSE ORGANS
1. General
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receptors for light, vibrations, chemicals, equilibrium, gravity
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cuticle modified to form a vast array of receptors (sensilla)
2. Sensilla
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specialized for various environmental events
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consist of:
<>modified cuticle, usually a seta
<> a modified cilium
<> sensory neurons
<> support cells
3. Mechanoreceptors
a. Trichobothria
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extremely sensitive mechanoreceptors detect weak, low velocity air currents
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a long, slender, solid seta
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especially common and important in arachnids
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a blinded spider can capture flies using its trichobothria
4. Chemoreceptors
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detect chemicals
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modified hollow setae with substrate-specific chemosensory neurons
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chemoreceptive sensilla resemble mechanoreceptive setae
5. Equilibrium and Gravity
a. Statocysts
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several malacostracan crustaceans have statocysts
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analogous to the vestibule of the vertebrate inner ear
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detects gravitational field and acceleration
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6. Tympanal Organs
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some arthropods can hear, i.e. detect vibrations in air
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tympanal organs are present in several insect groups
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cicadas, crickets, grasshoppers, moths
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a thin sheet of cuticle (eardrum) over an opening
7. Hygroreceptors
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humidity receptors
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very important to terrestrial arthropods
8. Photoreceptors
a. General
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widespread, often well-developed and sophisticated
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two types:
<>"median" pigment-cup ocelli
<>"lateral" compound eyes
<>both often present in the same individual
REPRODUCTION
1. General
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most arthropods are gonochoric
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fertilization may be external or internal in aquatic arthropods
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always internal in terrestrial species
2. Sperm Transfer
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sperm transfer usually by mating or copulation
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females usually store the sperm in a seminal receptacle
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3. Spermatophores
a. General
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many arthropods transfer sperm in packets
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an adaptation for sperm transfer on land
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male abandons spermatophore for female to find or may place it in the female
gonopore
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most insects use copulation
4. Copulation
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present in many aquatic arthropods (crustaceans), also in derived terrestrial forms
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often with courtship and behavior patterns
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anatomical equipment for internal fertilization by copulation
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male inserts an intromittent organ into the reproductive tract of the female
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deposits sperm or spermatophores into her seminal receptacle
Arthropod Development
Nauplius
Zoea
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Megalops
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Arthropods maintain homeostasis
Circulation and respiration :
 Open hemocoel as a result of hard exoskeleton and lack of internal segmentation.
 Muscular heart required since body movements can’t move blood.
 Hemolymph has amebocytes, pigments, and some have clotting factors.
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Osmoregulation and waste excretion :
 Closed structure required since open nephrostome wouldn’t with such a large
hemocoel.
 Material uptake depends on filtration pressure and active uptake.
Reuptake of salts and nutrients
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How do Arthropods maintain homeostasis?
Antennal and maxillary
glands in crustaceans.
 Produce ammonia with
some urea and uric acid.
How do Arthropods maintain homeostasis?
Malpighian tubules in arachnids
and insects.
Blind tubes extend into
hemocoel and empty into gut.
Produce uric acid.
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Reproduce and develop
 Usually some brooding.
 Development often mixed with early brooding then larval stages.
 Eggs centrolecithal but amount of yolk varies (so does cleavage).
Symbiosis
scarlet
cleaner
shrimp
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