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08 Sept. 2014 Arthropoda.ppt 2
Phylum Arthropoda
• Phylum Arthropoda • Greek: arthro = jointed, + pod = foot
• Huge group, > 1,000,000 species.
• estimate: 1,000,000 spp. arthropods
1,190,000 spp. animals
• ~ 84% of all animal species are
arthropods!!
08 Sept. 2014 Arthropoda.ppt 3
Phylum Arthropoda
• Body pla n
• Tube-in-tube, bilateral symmetry,
protostomous, “split” coelom
• Marine, aquatic, terrestrial • even Antarctica !
• Cell and tissue organization
• Triploblastic, complex organs
• ~ 30,000 genes in genome, (same as for mammals)
08 Sept. 2014 Arthropoda.ppt 4
Phylum Arthropoda
• Huge group, > 1,000,000 species.
• How can we explain the success of the
arthropods?
�Exoskeleton!
08 Sept. 2014 Arthropoda.ppt 5
Phylum Arthropoda
• Exoskeleton of chitin and protein (= cuticle)
• structure:
• epicuticle (oily, waxy)
• exocuticle (chitin & protein)
• endocuticle (chitin only)
• epidermis secretes cuticle
08 Sept. 2014 Arthropoda.ppt 6
Problems associated with exoskeleton.
• Problem 1. MOVEMENT
• Solution: Joints in
exoskeleton.
• arthro-, = joint
• -pod, = leg, foot
• Exocuticle absent from
joints; may form hinges.
• Endocuticle alone allows
flexibility.
08 Sept. 2014 Arthropoda.ppt 7
Problems associated with exoskeleton.
• Problem 2. GROWTH
• Solution: Molting
08 Sept. 2014 Arthropoda.ppt 8
Molting (1)
• Secretion of "molting
fluid" to dissolve old
endocuticle.
08 Sept. 2014 Arthropoda.ppt 9
Molting (2)
• New cuticle formed
under old exocuticle.
• Break out of old
cuticle
• Old cuticle breaks at
line of weakness
08 Sept. 2014 Arthropoda.ppt 10
Molting (3)
• Inflate with water/air to
increase size while
skeleton soft,
• but soft skeleton &
gravity limit size;
• arthropods are mostly
small.
• Hardening of new
exocuticle.
08 Sept. 2014 Arthropoda.ppt 11
Growth stages
• Arthropod passes thru
3-20+ growth stages in
life cycle.
• Some stop molting as
adults (insects, most
spiders)
• Some continue to molt
(crayfish, tarantulas)
08 Sept. 2014 Arthropoda.ppt 12
Problems associated with exoskeleton.
• Problem 3. SENSORY INPUT
• touch
• sensory setae connected to neurons
• smell & taste
• hollow sensory setae w/ chemosensitive nerve endings
08 Sept. 2014 Arthropoda.ppt 13
Problems associated with
exoskeleton.
• Problem 3. SENSORY INPUT
• vision
• clear cuticle over compound or simple eyes
08 Sept. 2014 Arthropoda.ppt 14
Problems associated with
exoskeleton.
• Problem 3. SENSORY INPUT
• hearing
• tympanum = endocuticle, vibrates like eardrum
• trichobothria (right �)
08 Sept. 2014 Arthropoda.ppt 15
Benefits of Exoskeleton: to individuals:
• Support
• Locomotion
• lever system
• walk, swim, fly
• Mechanical protection (armor)
• Retards evaporation (in air) and/or osmosis
(in water)
• water balance.
08 Sept. 2014 Arthropoda.ppt 16
Benefits of Exoskeleton: to the phylum:
• Reduction of coelom & segmentation
• Abandoned hydrostatic system of annelid-like
ancestor)
• Coelom reduced to pericardial cavity
• Segments fused = Tagmosis
• Specialization of body regions (= tagmata)
• Specialization of appendages
08 Sept. 2014 Arthropoda.ppt 17
Tagmosis
• Head (~ 4-6 segments)
� feeding, sensation
• Head appendages
• mandibles,
• maxillae,
• maxillipeds,
• chelicerae
• antennae
08 Sept. 2014 Arthropoda.ppt 18
Tagmosis
• Thorax (~ 3-6 segments)
• locomotion, grasping.
• Thoracic appendages
• walking legs,
• wings
• chelipeds
08 Sept. 2014 Arthropoda.ppt 19
Tagmosis
• Abdomen (~8- 30+ segments)
• respiration, reproduction, etc.
• Abdominal appendages
• abdominal gills (aquatic insect larvae)
• swimmerets (crayfish)
• filtering legs (barnacles)
• gonopods (crayfish, etc.)
• spinnerets (spiders)
08 Sept. 2014 Arthropoda.ppt 20
Tagmosis
• Number of segments/legs in each tagma varies by
subphylum, class.
– Cephalothorax of 6 segments in Chelicerata
• 1 pr. chelicerae
• 1 pr. pedipalps
• 4 pr. walking legs
– Cephalothorax of 13 segments in Crustacea (shrimps)
• 2 pr. antennae
• 1 pr. mandibles
• 2 pr. maxillae
• 3 pr. maxillipeds
• 5 pr. walking legs (1st pair modified as chelipeds)
08 Sept. 2014 Arthropoda.ppt 21
Phylum Arthropoda
• Ways the needs of cells are met
• Food
• Herbivores, predators, detritivores, parasites, filter
feeders, . . .
• O2 and CO2 exchange
• Gills—usu. modified legs,
• Book lungs,
• Tracheal systems
• Waste removal
• Diffusion from gills, Malphigian tubules
08 Sept. 2014 Arthropoda.ppt 22
Other arthropod characters
• Open circulatory system • Dorsal heart pumps hemolymph over brain
• Hemolymph moves through hemocoel back toward heart
• Ostia (holes) in sides of heart let hemolymph in to go around
again.
Phylum Arthropoda
• Special concerns of a
multicellular animal
• Circulation: Open
circulatory system,
(analogous to that in
Mollusca)
• Dorsal aorta
• Hemocoel
• Pores (ostia) valved
• Text fig. 42.3
08 Sept. 2014 Arthropoda.ppt 23
08 Sept. 2014 Arthropoda.ppt 24
Other arthropod characters
• Respiratory systems
• Gills in aquatic/marine arthropods
• Book lungs (modified gills) in spiders & scorpions
• Tracheal systems in most terrestrial arthropods
08 Sept. 2014 Arthropoda.ppt 25
Other arthropod characters
• Nervous system resembles that of annelid
• Dorsal brain with nerves around esophagus
• Paired ventral nerve cords
• Segmental ganglia
• Often fused into 1-2 ganglia in each tagma
08 Sept. 2014 Arthropoda.ppt 26
Phylum Arthropoda
• Special concerns of a multicellular
animal
• Circulation:
• Open circulatory system,
• Coordination,
• Complex sensory organs, nervous system
• Structural support & Movement
• Exoskeleton & muscles
• Maintenance of homeostasis—water balance.
08 Sept. 2014 Arthropoda.ppt 27
Phylum Arthropoda
• Reproduction
• Usually sexual, some parthenogenic
08 Sept. 2014 Arthropoda.ppt 28
Distinguishing Characters of Arthropoda
• Jointed exoskeleton
• Tagmosis
• Compound eyes
08 Sept. 2014 Arthropoda.ppt 29
Classification of Arthropoda
• Subphylum Trilobita
• Subphylum Chelicerata
• Subphylum Myriopoda
• Clade Pancrustacea
� Subphylum Crustacea (polyphyletic)
� Subphylum Hexapoda
08 Sept. 2014 Arthropoda.ppt 30
Classification of Arthropoda
• Subphylum Trilobita
�Class Trilobita
• Three-lobed head &
body (left, middle,
right)
• Diverse in Paleozoic
~540-240 MYA
• Extinct
08 Sept. 2014 Arthropoda.ppt 31
Classification of Arthropoda
• Subphylum Chelicerata
• Cephalothorax
• Jaws are chelicerae
• Pedipalps
• 4 pr. Walking legs
• Abdomen
08 Sept. 2014 Arthropoda.ppt 32
Classification of Arthropoda
• Subphylum Chelicerata
�Class Horseshoe crabs • Horseshoe crabs
• Scorpions ??
08 Sept. 2014 Arthropoda.ppt 33
Classification of Arthropoda
• Subphylum Chelicerata
�Class Arachnids – Lost compound eyes
• Spiders
• “Daddy-long-legs”
• vinegaroons
• mites & ticks
• more
• Scorpions ??
08 Sept. 2014 Arthropoda.ppt 34
Classification of Arthropoda
• Subphylum Myriapoda
• Legs unbranched
• Head & body
�Class Centipedes
• 1st legs are “fangs”
08 Sept. 2014 Arthropoda.ppt 35
Classification of Arthropoda
• Subphylum Myriapoda
�Class Millipedes
• Double segments (2 pr. legs per segment)
08 Sept. 2014 Arthropoda.ppt 36
Classification of Arthropoda
• Clade Pancrustacea
• Subphylum Hexapoda
• Subphylum Crustacea
• 2 pr. Antennae
(antennules, antennae)
• Cephalothorax
• 13 segments &
appendage pairs
• Abdomen
• variable among Classes
08 Sept. 2014 Arthropoda.ppt 37
Classification of Arthropoda
• Subphylum Crustacea
�Class “crabs”
�Class barnacles
08 Sept. 2014 Arthropoda.ppt 38
Classification of Arthropoda
• Subphylum Hexapoda
�Class Insects
• Head, thorax, abdomen
• 2 pr. Wings
• ~800,000 species,
majority of all arthropods
08 Sept. 2014 Arthropoda.ppt 39
Classification of Arthropoda
• Subphylum Hexapoda
�Class Insects
• Incomplete metamorphosis
• Dragonflies
• Orthoptera
• Hemiptera, Homoptera
• Complete metamorphosis
• Coleoptera (beetles)
• Hymenoptera (wasps, ants,
bees)
• Diptera (flies)
08 Sept. 2014 Arthropoda.ppt 40
Why are Arthropods so successful?
• Exoskeleton � tagmosis � evolution of
flight � speciation � 106 species of
insects.