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Arthropods
Blue print for Success
Arthropod Characteristics
• Includes crayfish, lobsters, spiders, mites,
scorpions, and insects
• Metamerism modified by the specialization of
body regions for specific functions
(tagmatization)
• Chitinous exoskeleton, support and protection
• Paired jointed appendages, ventral nervous
system
• Growth accompanied by molting, metamorphosis
• open circulatory system, complete digestive tract
Exoskeleton
• Major reason for Arthropod success
• Provides structural support, protection, impermeable
surfaces to prevent water loss, and a system of levers
for attachment of muscles and movement
• Exoskeleton made of two layers
• -outer of waxy lipoprotein, prevents dehydration and
impermeable to microorganisms
• -Inner of chitin, tough polysaccharide and protein
• Hardens by deposition of calcium carbonate
• Joints had to be incorporated with flexible membrane
Exoskeleton
Exoskeleton
Exoskeleton
Exoskeleton
• Molting is necessary to permit growth, 4 steps
• -Enzymes secreted to separate exoskeleton
from procuticle
• -New procuticle is secreted
• -Animal swells by air or water intake, old
exoskeleton is split along ecdysal lines
• New exoskeleton hardens by addition on
calcium carbonate, takes few hours to days
and animal is vulnerable, remains hidden
Molting
molting
Exoskeleton
Arthropod Anatomy
• Hemocoel serves as a cavity for the open
circulatory system, the rigid exoskeleton
means the coelom is no longer a hydrostatic
skeleton
• Internal organs are bathed in body fluids to
exchange nutrients, wastes and sometimes
gases
• Metamorphosis- radical change in body form
from larva to adult, eliminates competition
between larval and adult stages for food
Subphylum Trilobitomorpha
• Trilobite body has three longitudinal sections
thus the name
• Dominant life form in the cambrian period 600
million years ago to 345 million years ago
• Body was oval, flattened and could roll into a
ball for protection
• Appendages had two lobes Biramous, inner
for walking and outer had spikes for digging
Trilobite
Trilobite
Trilobites
Subphylum Chelicerata
• Spiders, mites, ticks, horseshoe crabs and sea
spiders
• Two Tagmata: cephalothorax- contains
sensory, feeding and locomotion structures
Opisthosoma- contains digestive,
reproductive, excretory and respiratory organs
• First pair of appendages are pincerlike or
chelate (claws) or specialized hollow fangs
• Pedipalps- second pair appendages, sensory
or feeding, locomotion
• Third pair appendages walking legs
Class Arachnida
• Majority of spiders mites ticks and scorpions
are harmless or beneficial to humans
• Sea scorpions dated to 425 million years ago
and other arachnids date to 345 million years
ago
• Most are carnivores, either pour or inject
enzymes over prey and digested tissue is
eaten or sucked in
• The front portion of the gut is modified into a
pumping stomach, mid gut and hind gut
complete digestion
Arachnid Anatomy
• Nitrogenous wastes are collected with coxal
glands or malpighian tubules, both collect
nitrogenous wastes from blood
• Coxal exit at bottom of posterior appendages
• Malpighian tubles deposit excretory wastes
into gut tract and exit with digestive wastes
• Book lungs exchange gases thru lamella that
air passes thru from ventral slit on abdomen
• Trachea are tubules which deliver air directly
to body tissues exit thru side of abdomen
Order Araneae
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Spiders- largest order of Arachnids
Chelicerae with poison glands and fangs
Six to eight eyes
Spinnerets- conical projections associated
with silk glands
• Silk is a protein, different types produced for
different sections of web
• Stronger than Kevlar (steel) Elastic
• Safety Line, Ballooning, wrap eggs
Spider Multiple Eyes, Setae
Spider
Order Acarina
• Mites and Ticks, many are ectoparasites, some
free living terrestrial and aquatic
• Chelicerae and pedipalps are modified for
piercing, biting, anchoring and sucking
• 4 pairs of walking legs (adults)
• Chiggers larva break down and suck host skin
• Dust mites (allergen), scabies tunnel under
human skin
• Ticks transmit rocky mount. Spotted fever,
lyme disease
Mite
Mite Infestations
Tick
Removing a tick
Ticks on wild Rabbit
Horseshoe Crab
Sea Spiders
Sea Spider
Sea Spiders
Order Scorpionida
• Range tropical to warm temperate areas
• Nocturnal and secretive Hide under logs,
stones during day
• Chelicera- Jaws
• Chelate pedipalps- Claws
• Stinger at base of postabdomen (tail)
• Only a few toxic to humans in north Africa
Mexico and southwest U.S., most sting like a
wasp
Scorpion
Scorpion with Babies
Subphylum Crustacea
• Crayfish, shrimp, Lobster, crabs, copepods,
cladocerans, fairy shrimp, isopods, amphipods
and barnacles
• Two pairs of antennae and Biramous
appendages
• Basal segment- endopodite medial ramus
exopodite lateral ramus
Class Malacostraca
• Crabs, Lobster, Crayfish, shrimp, mysids, Krill,
isopods and amphipods
• Class Decapoda crab, lobster shrimp
• Shrimp muscular abdomen for swimming
• Lobster, Crabs crawl on bottom
• Abdomen of crabs greatly reduced
• Cephalothorax- fusion of head and thorax,
shield like Carapace
Maine Lobster
Florida Lobster
Ghost Crabs
King Crab
Crab Larva Zoea
Crayfish Anatomy
Crayfish Anatomy
• Appendages – 1 first Antennae, shorter
2 second antennae, longer
• Appendages 3 mandibles for chewing
4 maxillae food handling
5 maxillae food handling, small gill, blade
called gill bailer for circulating water over gills
• Appendages 6-8 Maxillipeds sensory and food
handling
• Appendages 9-13 peropods walking legs