Phylum Arthropoda
Arthropod Characteristic
= “jointed limbs”
Segmented body = metamerism
= grouped into 2/3 regions
Paired segmented appendages
Chitinous exoskeleton
Tubular alimentary canal
Coelom reduced to hemocoel
Open circulatory system
Respiration by gills, tracheae
or spiracles
Anterior ganglion, paired
connectives & nerve cords
Malphigian tubes = excretion
Separate sexes
Arthropod Fun Facts
You are here!
Aphids are born pregnant
No two spider webs are alike
Adult bed bugs can survive 1 year
without food
Hornet sting has highest
concentration of AChE
Bed houses 6 billion dust mites
Ant queen can live 15 years
Dragon flies can reach 60 MPH
Each year insects eat 1/3 earth’s
food crop
Citronella irritates mosquito feet
Mosqitos prefer children to
adults, blondes to brunettes
Arthropod Fun Facts
Lobster blood = blue, insect =
yellow
Flea leap = greater acceleration
than space shuttle
Black widow venom more
powerful than rattlesnake
Parasitic wasp = smaller than
housefly eye
More insects in 1 mile2 than
humans on earth
Honeybee kills more people than
poisonous snakes
Among the deadliest insects are
kissing bugs and African ants
Arthropod Generalized Bauplan
1. Longitudinal view
Three distinct sections or tagmata: head, thorax and
abdomen (different classes have slightly different names)
Head = antennae, mouthparts, tightly fused = cranium =
difficult to determine # of segments involved
Thorax = locomotor part of the body, three segments
(often fused)
Abdomen = may or may not contain appendages
Arthropod Generalized Bauplan
2. Appendages
Lack ciliation for
movement = even
during larval stages
Problem = rigid
exoskeleton
Solution = appendages
of plates and
cylinders
Skeleton + muscles =
leverage
Adapted for different
functions on types of
locomotion
Uni- or biramous
Arthropod Generalized Bauplan
3. Cross section
Loss of coelom associated with open circulatory system
Hemocoel = internal organ are bathed in body fluids
Body size demands pumping organ
Cephalization, ganglions due to metamerism
Arthropod Generalized Bauplan
4. Exoskeleton
= secreted by epidermal cells
Epicuticle = outermost, hard protein cross link, waxy
lipoprotein (cement layer, waxy layer and cuticulin)
Procuticle = bulk of exoskeleton, made of exo-and
endocuticle, flexible, composed largely of chitin,
strengthened by calcium
Moulting or Ecdysis
Involvement ecdysone (hormone)
a) Old skeleton detached from
epidermis
b) Epidermis secretes epicuticle
c) Enzymes degrade exoskeleton
d) Secretion of new procuticle
e) Old skeleton splits
f) Extrication from old skeleton
g) “Sclerotinization” = tanning
h) Some animals consume old
skeleton
Generalized Bauplan Differentiation
Subphylum Cheliceriformes
Cheliceriformes Characteristics
65,000 described species
Some paleozoic forms were
2 m length
Rich fossil record
Most species live on land
Mites secondarily inhabited
aquatic habitats
Body composed of:
Prosoma = cephalothorax (6
segments)
Opisthosoma = abdomen (12
segments)
! bearing telson
Book lungs or gills
Cheliceriformes Characteristics
Appendages: chelicerae,
pedipalps, walking legs
= multiarticulate/uniramous
Excretion by coxal glands/
Malphigian tubules
Simple medial eyes,
sometimes compund eyes
Most gonochoristic/
dioecious
Class Chelicerata
Subclass Merostomata
Preserved specimen of
Limulus polyphemus
1. Carapace
2. Telson
3. Compound eye
4. Anterior spine
Called horsefoot by Thomas Hariot
Harmless and non poisonous
Telson used as lever or rudder
Asian horseshoe crabs = delicacy (up to $50/animal,
American horseshoe crabs = bait ($1-2/animal)
1
2
3
1. Chelicera
2. Pedipalps
3. Walking legs
4. Chilaria
Ventral view of
abdomen of Limulus.
1. Genital operculum (covering genital pores)
2. Gill opercula (covering book gills)
3. Carapace
5. 4th chelate walking leg
Hemolymph = analogous to human blood
Oxygen carrying protein = hemocyanin
Breeding grounds = Delaware Bay
Whelk fishermen use 20-25,000
horseshoe crabs annually as bait
Subclass Arachnida
Carapace-like shield
Opisthosoma
appendages modified
= spinnerets/pectines
Book lungs
Almost all terrestrial
Over 60,000 species
Carnivorous
Eyes and tactile hairs
1. Eyes
2. Chelicerae
with fangs
3. Pedipalps
1
Spinnerets
2
3
The “Joy” of Spider Reproduction
Gonochoristic
Sexual dimorphism
Intricate mating duels
(other males)
Courtship
Sperm deposited in web
Fertilized eggs in silk
cocoon
Spider Art
Class Pycnogonida
= sea spiders
600 species
Carnivores
Dt extends
into legs
Cold water