ARTHROPODA

Phylum Arthropoda
Phylum Arthropoda
Most “successful” lineage on Earth
greatest
biomass (>750 kg per person)
numbers of species
numbers of individuals
number of ecological niches
Phylum Arthropoda
Subphylum Trilobitomorpha
Class Trilobita
Subphylum Chelicerata
Class Merostomata
Class Pycnogonida
Class Arachnida
Subphylum Mandibulata
Class Crustacea
Class Myriapoda
Class Hexapoda
From: Briggs & Fortey (2005) Wonderful strife: Systematics, stem groups, and the
phylogenetic signal of the Cambrian radiation. Paleobiology supplement to Vol 31(2): 94-112
ARTHROPODA
Why so successful?
1. Exoskeleton
-allowed invasion of land & flight
2. Metamerism & limbs
-allowed incredible limb modifications
3. Short life span & high fecundity
-allows higher rates of evolution
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Subphylum Chelicerata
Subphylum Chelicerata
Apomorphies
• No antennae (lost)
• Chelicerae
• Two tagmata
– Prosoma & Opisthosoma
(no distinct head)
Subphylum Chelicerata
Chelicerae
first two appendages modified for
feeding, clawed - not mandibles
Subphylum Chelicerata
Chelicerae
chelate (pinching)
or venomous fangs
or piercing stylets
(for sucking body
or plant juices)
Sun scorpion
Subphylum Chelicerata
Pedipalps - 2nd pair of appendages
modified for sensory perception
communication
catching prey
conveying sperm
(spiders)
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Subphylum Chelicerata
Pedipalps
Subphylum Chelicerata
12 appendages
1 pair of chelicerae
1 pair of pedipalps
4 pair of walking /swimming legs
(3 pair in immature mites & Ricinulei)
(1st pair sensory in many groups = 3 pair for walking)
Most species are predators
Most are liquid feeders (don’t chew)
Gnathobases - grind prior to ingestion
Subphylum Chelicerata
Subphylum Chelicerata
Three classes
• Merostomata
– relic, 4 species left
• Pycnogonida
– marine “sea spiders”, 1,000 spp.
• Arachnida
– spiders, scorpions, etc. 70,000
spp.
Subclass Xiphosura
Class Merostomata
Order Xiphosura - Horseshoe crabs
Horseshoe crabs not crabs (not Crustaceans)
closest extant relatives of
eurypterids & trilobites
• 4 species left (3 genera: NA, se Asia, Malaysia)
“trilobite larva”
– “living fossil” “evolutionary relic”
• all marine, shallow (but oviposit on shoreline)
• only chelicerates with compound eyes
• primitive ! simple!
3
Class Arachnida
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Class Arachnida
• primarily terrestrial (marine origin)
– few mites & spiders secondarily aquatic
(some mites parasitize marine animals &
some live in deep ocean trenches)
• ~ 93,000 species
Class Arachnida
Among the earliest animals on land
– Tracks 460-500 mya ?
– Most activity from the Devonian (410360 mya)
– Fossil mites, scorpions, spiders
– 1 m long aquatic /amphibious scorpions
• Most are spiders (37,000 spp) &
mites (45,200 spp)
Class Arachnida
• Respiration via 2-4 pairs of book
lungs and / or rudimentary tracheae open via spiracles
• Tracheae not homologous with those
of other terrestrial arthropods (& not
as efficient = lower metabolic rates)
• Usually “sit & wait” predators
Class Arachnida
Class Arachnida
Pumping stomach
Species with
tracheae rely
less on blood for
gas exchange
(insects do not use
blood for gas
exchange)
Book lung
5
Spermatophore
Class Arachnida ~93,000 species
Orders
1. Aranae
2. Acari
3. (Solifugae) Solpugida
4. Uropygi
5. Amblypygi
6. Opiliones
7. Pseudoscopriones
8. Scorpiones
9. Schizomida
10. Rincinulei
11. Palpigradi
Life in the undergrowth
Data from: Coddington, J. A. & Colwell, R. K. 2001. Arachnids, pp.
199-219 in Encyclopedia of Biodiversity vol. 1 Academic Press.
No. described spp.
~37,000
~45,200 (~500,000 new?)
1,065
101
126
~4,500
3,100
1,260
195
53
80
We will focus on those indicated in bold
Class Arachnida
Ricinulei
Order Araneae - 7th largest animal order
• Spiders
– Spinnerets, silk glands
– Chelicerae modified into fangs - venom
tubes
– A few species dangerous to humans
• Black widow, brown recluse, hobo(?)
• Most spider “bites” are not
– All predators, (on insects)
SEM of Spider spinnerete & silk
Gasteracantha sp.
Silk proteins Spider silk used for:
prey capture
safety lines
egg sacks
aerial dispersal lines
air bags for diving
One of the strongest &
toughest natural fibers
known
5 times stronger than steel of
same weight & more elastic
than nylon
Crab spider:
Thomisidae
6
Jumping spiders
Salticidae
.
Orb-weavers
Araneidae:
Gasteracantha sp.
Courtship dances by jumping spiders (Salticidae)
by Dr. W. Maddison (UBC)
Class Arachnida
Order Acari
• Mites & ticks
– Hyperdiverse
– ~ 1 million undescribed
species
– rival nematodes &
beetles in species #
– Many parasitic
– Herbivores & predators
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Class Arachnida
Order Acari
• Prosoma & opisthosoma ~ fused
• Ticks - vector pathogens, e.g.
• Lyme disease (Spirochaete bacteria)
• Some plant pests
• “Chiggers” & mange
• Some aquatic spp.
Class Arachnida
Order Acari
• Demodex folliculorum
-the eyebrow mite
-harmless, usually
-cosmopolitan
- < 0.4 mm
Ixodidae: Amblyomma komodoense
8
Class Arachnida
Phalangium opilo L.
Order Opiliones
– “Daddy long-legs,” “Harvestmen”
– No venom
– 4,500 spp
– Tagma fused
– Trachea only
– Have penis
– Can eat solids
Class Arachnida
Order Pseudoscorpiones
– ~ 3,100 species
– Predaceous, in leaf litter & crevices
– Often phoretic on flying insects
– 7mm or less, usually 5 or less
– Pedipalps large, pincerlike, no tail
– Poison glands in pedipalps
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Class Arachnida
Order Scorpiones
– Terrestrial, largest bodied arachnid
– Large, chelate pedipalps
– 1,260 species
– Poison gland in tail
– Aquatic 425 mya
– Terrestrial 400 mya
– Nocturnal
Phylum Arthropoda
Subphylum Mandibulata
Good
with
curry!
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Phylum Arthropoda
Subphylum Trilobitomorpha !
Class Trilobita !
Subphylum Chelicerata !
Class Merostomata !
Class Pycnogonida !
Class Arachnida !
Subphylum Mandibulata
Class Myriapoda
Class Crustacea
Class Hexapoda
Subphylum Mandibulata
Subphylum Mandibulata
Concept of Snodgrass 1930-1950s
Three classes
• Myriapoda
– centipedes, millipedes, ~13,000 spp
• Crustacea
– shrimps, lobsters, etc. 45,000 spp.
• Hexapoda
– insects, 1,000,000+ spp.
Subphylum Mandibulata
Crustacea + Myriapoda + Insecta
Apomorphy
• Mandibles (biting jaws)
– Shared development & genetics
Crustacea
Hexapoda (Diplura)
Hexapoda (Thysanura)
Mandibles - developed from limbs
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Class Myriapoda
Class Myriapoda
Centipedes & Millipedes
Largely homonomous body
Class Myriapoda
Centipedes - Chilopoda
• 2,800 species (8,000 total?)
• Terrestrial (some marine?)
Direct development
(no larvae)
<1 - 30 cm
Class Myriapoda
• Unwaxed cuticle & un-closable spiracles =
moist habitats, nocturnal
• Genital opening posterior
Geophilomorpha
Centipedes - Chilopoda
Soil
Centipedes
• Predators
Common
• Poison fangs (1st limbs on trunk)
Defensively
produce HCN gas
• One pair of legs per
body segment
No. body
segments not
constant even in a
species
12
Scolopendromorpha
Scutigeromorpha
Dorsal spiracles!
Class Myriapoda
Class Myriapoda
Millipedes - Diplopoda
Millipedes - Diplopoda
• 7,000 species (80,000 total?)
• No venom
• Terrestrial
• Trunk of diplosegments (2 segments
fused) = 2 pair of legs per segment
• Detritivores, herbivores
• Genital opening anterior
• Many with calcium hardened cuticle (tough!
But also rare in acidic habitats)
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Hexapods
Phylum Arthropoda
Subphylum Trilobitomorpha !
Class Trilobita !
Subphylum Chelicerata !
Class Merostomata !
Class Pycnogonida !
Class Arachnida !
Subphylum Mandibulata !
Class Crustacea !
Class Myriapoda !
Class Hexapoda
Tagmosis & limb loss
in the Insecta
From hypothetical
worm-like & myriapodlike ancestors
CLASS HEXAPODA
Characteristics
• 6 walking legs (each of up to 6 segments)
• 3 tagmata
Note loss of limbs on
abdomen
Note incorporation of
limbs as mouthparts
CLASS HEXAPODA
Fossil History
No marine fossil hexapods? (Crustaceans?)
Oldest fossil hexapods ~ 400 mya
(Devonian)
• Cuticle tanned with sclerotin (a lightweight
protein)
• Abdomen originally of 11 segments
Reconstruction of
Rhyniella praecursor
Among the oldest
terrestrial animals
Devonian (400 mya)
order Collembola - Rhynie chert of Scotland
Rhyniella praecursor
14
Family richness
In fossil record
Order Collembola - Springtails
Fossil record
Labandeira & Sepkoski 1993
Phylogeny of the
Hexapoda
Collembola &
Archeognatha
Earliest Hexapods
Fig. 8.1
Fig. 7.2
Phylogeny of basal Hexapoda
Insecta
Fig. 7.3
© Dave Walter
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Subclass & Order Protura
Ectognathy!
• No antennae, wings, or eyes
– (pseudoculus)
see. p.230-231
• Entognathous mouth
– (mouthparts inside cavity)
• 400-600 species, 8 families
~ 48 species in North America
© Dave Walter
Subclass & Order Protura
• Small (0.6-1.5 mm)
see. p.230-231
• Prolegs modified for sensory
purposes
• Tracheal system reduced
• Anamorphosis - autapomorphic.
Immature has few segments & more
are added posteriorly during
development
Functionally a tetrapod
Subclass & Order Protura
• Inhabit soil, decaying vegetation, and rotting
wood
• Associated with fungus (thought to
feed on mycorrhizal fungi)
• Rare in collections, no? specialist
in North America
• Rarely seen alive - collected with
Berlese funnels (as are Diplurans)
Subclass & Order Collembola
• Abdomen reduced to 6 or fewer segments
– Tracheal system reduced / absent
• Entognathous mouth ( & no palps)
– (mouthparts inside cavity)
• 6,000-9,000 species, 700 in North America
• Many undescribed spp.
© Dave Walter
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Subclass & Order Collembola
• Abdominal seg 1 has collophore
– Used for many purposes, incl. osmoregulation
• Furca - “spring tail” a forked jumping organ
• Small 2-3 mm, up to 12mm
• With postantennal sensory
organs (possible
homologs of Crustacean
2nd antennae)
• Molting continues for life (52 molts is the record)
• Feed on decaying vegetation, fungi, etc.
Subclass & Order Collembola
• Ubiquity similar to Acari & nematodes
– but not as many species
• Ubiquitous & abundant (100,000+ / m
3 of surface soil &
most common insect on Antarctica, -20m in fresh & marine habitats,
Coenaletidae species live in shells with terrestrial hermit crabs!)
• Found in all habitats that contain metazoans
– coldest to hottest (48°C volcanic vents)
– treetops to deepest soils
– some species can survive desiccation
(anhydrobiosis, completely dry without death)
– some species can survive without oxygen
(more likely to survive nuclear war than cockroaches!)
Symphypleona
- globular
Life in the undergrowth - Collembola
First 4 abdominal segments fused
Arthropleona
- elongate
Life in the undergrowth - Collembola - mating
(Spermatophore placed on substrate)
Which do you think
is more derived?
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Archeognatha
© Alex Wild
Palaeodictyoptera
Dominant insects of the
Paleozoic
(50% of species)
Beaked herbivores
(83% of Permian leaf fossils showed evidence of
herbivory)
“Paleoptera”
&
Neoptera
Fig. 7.2
End Permian extinction of
superorder (multiple closely related
paleopteran orders)
Prothoracic paranotal lobes
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Order Odonata - Dragon & Damselflies
• 5,500 species, mostly tropical, predacious
• Nymphs with extensible pre-hensile labial mask
modified for grasping prey
• Male copulatory organs on segments 2&3 but
gonopore on segment 9
copulate in unique
‘wheel position’
• 360° vision - aerial
hunters
Phylogeny of the
Hexapoda
Order Odonata - Dragon & Damselflies
• Two suborders hold 99% of species
• Dragonflies: Anisoptera
– Wings to side, larvae with rectal gills
• Damselflies: Zygoptera
– Wings vertical, larvae with 3 caudal lamellae (gills)
Phylogeny of the
Hexapoda
Neoptera - 90% of Hexapoda
Polyneoptera - Orthopteroids
Paraneoptera - Hemipteroids
Endopterygota (Holometabola)
Fig. 7.2
Fig. 7.2
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20
Grasshoppers - Acrididae
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Katydids - Tettigoniidae - Tettigonia chinensis
Phylogeny of the
Hexapoda
Phylogeny of the
Hexapoda
Neoptera
Polyneoptera - Orthopteroids etc
Paraneoptera - Hemipteroids
Endopterygota (Holometabola)
Fig. 7.2
Fig. 7.2
Order Phthiraptera - lice
• Dorsoventrally flattened
• ~ 5,000 species (we have 2 species)
• Eyes absent or reduced
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Phylogeny of human head/body louse
Deep (old) split within the louse
phylogeny
1.18 million years ago
How is this possible if modern Homo
sapiens is less than 0.2 million years
old?
H. neanderthalensis [0.6 mya]
H. erectus [1.8 mya]
Order Hemiptera
Phylogeny of human head/body louse
•
Mapped onto phylogeny
of genus Homo
Bugs, hoppers, aphids, cicadas, scale
insects, whiteflies, etc.
• Largest non-endopterygote order
(~90,000 spp)
• Mandibles and maxillae modified
as piercing stylets
• Lack palps
• In beak-like labium
= rostrum or proboscis
• Wings coupled in flight - fore & hind
act as one wing
H. neanderthalensis is
too recent
Deep split is consistent
with split between
H. erectus and our lineage
one possible scenario
Box 11.8
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Order Hemiptera
Fig. 7.5
“Homoptera” - Sternorrhyncha
psyllids, whiteflies, aphids, scale insects
“Homoptera” - “Auchenorrhyncha”
Cicadas, spittlebugs, plant-, leaf-, & treehoppers
- with tymbal acoustic system
Cicadidae
Cicadellidae
Coccoidea - coccids, scales, mealy bugs
Gerromorpha: Gerridae
Flatidae
Cercopidae
Nepomorpha: Corixidae
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Cimicidae
Cimex lectularius
Swallow bugs
Cimicomorpha
Assassin bugs
Plant bugs
Lace bugs
Minute Pirate bugs
Bed bugs
Fig. 7.2
Carabidae
Staphylinoidea
Scarabaeoidea
Cucujiformia
Cerambycidae
Chrysomelidae
Curculionidae
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Fig. 7.2
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Order Siphonaptera - fleas
• 2,500 species, apterous, laterally compressed
• Ectoparasites of birds & mammals
~ 74% use rodents as hosts
• No compound eyes, (ocelli or none)
• Piercing & sucking mouthparts
• DNA & new morphological data suggest fleas
evolved from within the Mecoptera (sister to
snow fleas - Boreidae)
Order Trichoptera - caddisflies
• Aquatic larvae with hook-bearing prolegs at
end of abdomen
• Larvae make cases, or are free-living
• Sister order to the Lepidoptera - Very well
supported
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Order Trichoptera - caddisflies
• Wings with hairs, rarely scales
• ~11,000 species with moth-like adults
• Diverse feeding habits - predators, detritivores,
adults often do not feed
Aquatic Hexapods - 30,000 species (370 marine)
Major contributors
• Odonata
• Ephemeroptera
• Plecoptera
• Hemiptera
• Megaloptera
• Coleoptera
• Diptera
• Trichoptera
Minor contributors
• Collembola
• Neuroptera
• Hymenoptera
• Orthoptera
• Lepidoptera
• Blattodea
Order Lepidoptera - moths
Order Lepidoptera - moths
• “Microlepidoptera” - 40% of species
• Antennae typically filiform or plumose
(moths) or knobbed / clubed (butterflies)
– small
– Lots of leaf miners
• Macrolepidoptera - 60% of species
– Larger bodied
– With tympanal organs in some lineages (Many are
tuned to detect bat sonar)
• Butterflies are modified, diurnal moths
• “moths” paraphyletic with respect to
butterflies
• ~160,000 species (14,500 butterfly species)
Butterflies - 82 Alaskan species, Ken Philip
28
Silk moths - Saturniidae
1,500 species
Order Hymenoptera - ants, wasps, bees
• Flight driven by forewings - hindwings coupled to
forewings with small hooks (hamuli)
• ~100,000 species (36,000 in NA - more than Coleoptera;
may outnumber global Coleoptera due to many tiny parasitoid
wasps; estimated that 60-96% of the order is undescribed)
• Many species beneficial to humans - pollinators &
parasitoids (biocontrol)
• Haplodiploidy - females diploid, males haploid
Order Hymenoptera - ants, wasps, bees
Traditionally, two suborders:
– “Symphyta” (wood wasps & sawflies)
• 3 segmented thorax
• Larvae caterpillar-like & phytophagous
– Apocrita (ants, bees & wasps)
• Propodeum (abdominal segment 1) joined to thorax =
mesosoma remainder of abdomen is the gaster
(or metasoma)
• One clade with ovipositor modified into sting
Order Hymenoptera - ants, wasps, bees
Four basic life patterns:
1. the primarily phytophagous “Symphyta”
2. the parasitic or gall-making Apocrita
3. the non-social Apocrita whose larvae are
fed prey or pollen captured by the mother
4. the social Apocrita
29
Prolegs continuous to posterior
Lepidoptera larvae not so - have a ‘gap’
30
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