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Phylum
Arthropoda
Phylum Arthropoda
• “Jointed Foot”
• Crabs, lobsters, spiders,
ticks/mites, insects,
centipedes, millipedes
• 85% of all known species
• Developed from Annelids
• First land animals some 300
million years ago.
Characteristics that
make Arthropods
successful
1.Metamerism
2.Exoskeleton
3.Appendages
4.Hemocoel
5.Metamorphosis
Metamerism
• Segmentation of body into
metameres modified by
tagmatization (specialization) of
segments
• Tagmata: head, thorax and
abdomen.
• All segments are integrated into
a single functioning unit.
Exoskeleton
• Made up of chitin (protein)
• Provides support, protects, and
minimizes water loss.
• Does not grow with animal so
must molt or ecdyse
– Vulnerable to attack or drying out
after the molt
• Heavy compared to body
• Move by contracting muscles
against exoskeleton
Appendages
• Paired, jointed appendages
adapted to function in:
– sensing their environment
– defending against predators
– swimming
– walking
– grasping
– transferring sperm
– generating water movement
– gas exchange
Hemocoel
• Reduced coelom
• Open circulatory system
• Like their exteriors, the internal
organs are generally built of repeated
segments.
• Ventral nervous system is “ladderlike” with paired nerve cord running
through all segments and forming
ganglia
• Complete digestive tract
Metamorphosis
• The changes in form that occur as
approach adulthood
Incomplete (Simple) Metamorphosis
• Juveniles and adults are similar in
appearance, differ only in size
• Egg Nymph Adult
Complete Metamorphosis
• Juveniles and adults have different
forms, often live in different habitats,
and may have very different behavior.
• Egg  Larvae  Pupa  Adult (most)
• Reduces competition between larval and
adult stages!
Five Subphyla of
Arthropoda
1. Trilobitomorpha
(extinct)
2.Chelicerata
3.Crustacea
4.Myriapoda
5.Hexapoda
Phylum Arthropoda:
Subphylum Chelicerata
• Over 60,000 species
• Possess chelicerae (fangs)
1. Class Merostomata
2. Class Arachnida
– Order
– Order
– Order
– Order
Scorpionida
Araneae
Opiliones
Acarina
3. Class Pycnogonida
Phylum Arthropoda
Subphylum Chelicerata
Class Merostomata
• Horseshoe crabs
• Similar to extinct trilobites
and present day scorpions
• 4 species
• Covered by hard horseshoeshaped carapace
• Blood used to create
bacterial test
Phylum Arthropoda
Subphylum Chelicerata
Class Arachnida
• Spiders, scorpions, ticks, mites
• Mainly terrestrial
• Two body regions
1. Cephalothorax
2. Abdomen
• Eight legs (4 pairs)
• Two other appendages attached to
cephalothorax
1. Chelicerae: claw-like fangs inject
poison
2. Pedipalps: aid in feeding and sensory
• Up to 12 simple eyes (most have 8)
detect light
Phylum Arthropoda
Subphylum Chelicerata
Class Arachnida
Order Scorpionida
• Scorpions
• 800 species
• Greatly enlarged
pedipalps to catch and
hold prey
• Abdomen tapers down to
stinger – injects venom
• Tropical areas
• Secretive and nocturnal
Phylum Arthropoda
Subphylum Chelicerata
Class Arachnida
Order Araneae
Spiders
34,000 species
All venomous
Sensory setae over entire body: detect movement
and pressure
• Skillful hunters
• Webs formed by spinnerets – secrete strong,
elastic protein
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– Silk used to line nests, cradle young, hold eggs and
sperm, and for ballooning
Order Araneae
• Feed by injecting enzymes into prey to dissolve body
substance and suck out liquefied remains
• Excretion (uric acid) through malipighian tubes
• Two Respiratory Strategies (most have both)
1.
Oxygen carried through body by tracheae (tubes) and
spiracles (slits in skeleton)
2. Blood circulated through book lungs (paged)  like gills
• Reproduction : Dioecious, solitary, complex mating
– Pheromones produced
– Internal fertilization – sperm on pedipalps enter under
female abdomen
– Oviparous – eggs hatch in about 2 weeks
Phylum Arthropoda
Subphylum Chelicerata
Class Arachnida
Order Opiliones
• “Daddy Long Legs”
• 6,500 species
• Omnivores &
Carnivores
• 1 segment, 2 eyes
Phylum Arthropoda
Subphylum Chelicerata
Class Arachnida
Order Acarina
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Ticks and Mites
30,000 species
Very small (some<1mm)
One body segment
Many carry diseases
Mostly parasitic: attach to skin and feed on
blood
Phylum Arthropoda
Subphylum Crustacea
• Mostly marine
• Chewing jaw called mandibles
• Two pairs of antennae
1. Class Malacostraca
– Order Decapoda
2. Class Branchiopoda
3. Class Maxillopoda
– Subclass Copepoda
– Subclass Cirripedia
Phylum Arthropoda
Subphylum Crustacea
Class Malacostraca
Order Decapoda
• Crabs, crayfish, shrimp,
lobster
• 15,000 species
• “Ten legs”
• Numerous segments grouped
into cephalothorax &
abdomen
• Maxillae: Used for holding
food
• Maxillipeds “jaw feet”
– Modified as mouthparts to
hold food and senses
touch/taste
• Periopods: 4 pairs of “walking
legs”
– One pair with Chelipeds
(claws)
– Bear the gills
• Pleopods: 5 pairs “swimming
legs”
– Swimmerets:
• used for swimming, water
movement over gills, and
reproduction (bear the sexual
organs)
– Uropod:
• Fused swimmerets used as
flipper/tail fin
Phylum Arthropoda
Subphylum Crustacea
Class Branchiopoda
• Water flea, tadpole
shrimp, clam shrimp, brine
shrimp or “sea monkey”
• Primarily freshwater
• Many produce “winter
eggs” that hatch in spring
Phylum Arthropoda
Subphylum Crustacea
Class Maxillopoda
Subclass Cirripedia
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Barnacles
Sessile
Mostly monoecious
Highly modified
Phylum Arthropoda
Subphylum Myriapoda
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Centipedes and millipedes
Over 13,000 species
Single pair of antennae
Simple eyes
Mandible
Between 10 to over 750 legs
1. Class Diplopoda
2. Class Chilopoda
Phylum Arthropoda
Subphylum Myriapoda
Class Diplopoda
• Millipedes
• 11 to 100 trunk segments with 2
pairs of legs/segment
• Rounded body
• Found mainly in tropical areas
• Feed on decayed plants
• Excrete foul-smelling or toxic
substances from stink glands
Phylum Arthropoda
Subphylum Myriapoda
Class Chilopoda
• Centipedes
• 15+ segments with 1 pair of legs
each
• More flattened body
• Some very colorful
• Poison claws
• Fast moving predators