Arthropoda
Characteristics of Arthropoda
• Segmented body (tagma & tagmatization)
• Hard exoskeleton (cuticle)of chiton + protein
• Paired, Jointed appendages
– Legs, antennae, feeding parts
Exoskeleton
• Can be thick/rigid or thin/flexible
• Functions:
–
–
–
–
Structural support
Muscle attachment
Protection
Prevents/reduces desiccation
• Facilitated colonization of land
• Must be molted
• Energetically costly
Arthropod Systems
Well developed sensory systems
• Eyes that produce visual images (compound & simple)
• Chemo (olfactory receptors)
• Inc. antennae which function as both chemo and tactile
receptors
Open circulatory system
• Hemocoel is main body cavity
Respriatory system
• Aquatic typically gills
• Terrestrial  internalized tubes
– Tracheal system
– Book lungs
Diversity
3 lineages, 4 main sub-phyla
• Chelicerata
• Myriapodia
• Pancrustaceans
– crustaceans
– Hexapoda (inc. insects)
Chelicerates (spiders, horseshoe crabs, scorpions, ticks, mites):
• Chelicerae
– Feeding appendages (fangs or “claws”)
• pedipalps
– sensing, reproduction, defense, manipulating food
• 2 body segments
– cephalothorax & abdomen
• Simple eyes (single lens) (often multiple
• No antennae
• uniramous
Figure 33.32
50 µm
Scorpion
Dust mite
Web-building spider
Arachnids (chelicerates)
Appendages
• 4 pairs of walking legs
• chelicerae—fangs which posses poison glands
• Toxin contains digestive enzymes that soften & semi digest the tissues of prey and
then they are slurped up the slurry.
• Pair of pedipalps
Book lungs
• Internalized, highly branched from lots of gas exchange.
• Stacked plates with spaces between, hemolymph flows next to spaces
Silk and webs:
• protein produced by glands in the abdomen
• spun by spinerette
• Each species produces a unique web and the spiders innately know how to create
it –genetically determined behavior
Myriapods — millipedes and centipedes
•
•
•
All living examples are terrestrial
Uniramous legs
Head segment: 1 pair of antanae, 3 pairs of appendages that are modified into
mouthparts which includes the jawlike mandible
Millipedes:
• Two pairs of legs/segment
• They are detrivores and/or herbivores
• Rounded in cross section
Centipedes
• One pair of legs/segment
• Dorsoventrally flattened
• Carnivores
– Poison claws (maxillaped) on the 1st trunk segment that paralyze prey and help in defense
Crustaceans (crabs, lobsters, shrimp, krill,
barnacles, isopods, copepods) exp. decapod
• Freshwater, marine, and some terrestrial
Appendages
• Biramous appendages
• Two pairs of antennae
• Walking legs on thorax
• Swimmerets on abdomen (marine versions only)
Segments:
• Cephalothorax
– Carapace w/ calcium carbonate
• abdoman
Crustaceans (crabs, lobsters, shrimp, krill,
barnacles, isopods, copepods) exp. decapod
Gas exchange
• Small ones  cuticle
• Larger  gills
Reproduction: aquatic crustanceans have larval stages
• Crustacean larvae help form a large part of the zooplankton
• Some adults (copepods) are also part of plankton
Barnacles—cuticle with calcium carbonate (refered to as a shell)
• Filter feeders filter with feeding appendages
• Glue themselves to substrate
Cephalothorax
Antennae
(sensory
reception)
Abdomen
Thorax
Head
Eye
Swimming appendages
(one pair per abdominal
segment)
Pincer
(defense)
Mouthparts
(feeding)
Walking legs
Figure 33.36
Hexapoda (6 legged arthropods – includes insects)
Appendages
• Antennae
• 3 pairs of walking legs
• uniraous
Segments
• 3 parts
– Head
– Thorax
• Many with two pairs of wings
• Extensions of exoskeleton, not limbs
• Adaptive advantage of flight
•
Abdomen
Reproduction:
• Dioecious
• Internal fertilization
• Sperm in spermatheca, fertilize egg at later time
• Incomplete v.complete metamorphosis
Abdomen
Thorax Head
Compound
eye
Figure
33.38
Antennae
Heart
Dorsal
artery
Crop
Cerebral ganglion
Anus
Vagina
Malpighian
tubules
Ovary
Tracheal tubes
Nerve cords
Mouthparts
•
Tracheal
system
Pores on surface  trachea  tracheoles tissues (perfuses
all tissues)
• Air sacs
• Both gas exchange and gas transport
• No hemolymph involved
Malphigian Tubules
• Terrestrial arthropods
• Closed tubes in hemoceol
• Actively transport waste
and ions (no filtration)
• Water follows osmotically
• Connects to rectum
• Rectum reabsorbs water
and ions
• Nitrogenous waste (uric
acid) released as solid w/
feces
Video: Butterfly Emerging
Figure 33.40
(a) Larva
(caterpillar)
(b) Pupa
(c) Later stage
(d) Emerging
pupa
adult
(e) Adult
Archaeognatha (bristletails; 350 species)
Figure
33.41
Zygentoma (silverfish; 450 species)
Winged insects (many orders; six are shown below)
Complete metamorphosis
Coleoptera
(beetles; 350,000 species)
Diptera
(151,000 species)
Hymenoptera
(125,000 species)
Proboscis
Lepidoptera
(120,000 species)
Incomplete metamorphosis
Hemiptera
(85,000 species)
Orthoptera
(13,000 species)
• Consult your lab guide for selected details
about specific insect orders