Download Limulus polyphemus.

Chapter 14
The Arthropods: Blueprint
for Success
Evolutionary Perspective
1.
2.
3.
4.
5.
6.
Metamerism modified by tagmatization
Chitinous exoskeleton
Paired, jointed appendages
Ecdysis
Ventral nervous system
Coelom reduced to cavity around
gonads
7. Open circulatory system
8. Complete digestive tract
9. Metamorphosis often present
Classification and Relationships
to other Animals
• Ecdysozoans
– Cuticle, ecdysis, loss of epidermal
cilia (figure 14.2)
• Monophyletic with five subphyla
(table 14.1)
– Chelicerata, Crustacea, Hexapoda,
Myriapoda, Trilobitomorpha (entirely
extinct)
Figure 14.2 Evolutionary relationships of the
arthropods to other animals.
Table 14.1
Metamerism and
Tagmatization
• Metamerism evident externally
– Segmental body wall
– Segmental appendages
• Metamerism reduced internally
– No septa
– Most organs are not metameric
• Tagmatization obvious
– Specializations for feeding, sensory
perception, locomotion, and visceral
functions
Learning Outcomes:
Section 14.3
• Describe the structure of the
arthropod exoskeleton or cuticle.
• Assess the influence the
exoskeleton has had on the
evolution of the arthropods.
The Exoskeleton
• Exoskeleton or cuticle
– External jointed skeleton
• Functions
–
–
–
–
Structural support
Protection
Prevents water loss
Levers for muscle attachment and
movement
• Covers all body surfaces and
invaginations
• Secreted by epidermis (hypodermis)
The Exoskeleton
• Epicuticle (figure 14.3)
– Lipoprotein
– Impermeable to water
– Barrier to microorganisms and pesticides
• Procuticle
– Chitin
• polysaccharide
– Outer procuticle hardened by sclerotization or
deposition of calcium carbonate
– Inner procuticle less hardened and flexible
• Articular membranes at joints (figure 14.4)
• Modifications include sensory receptors
– Sensilla
Figure 14.3 Arthropod exoskeleton.
Figure 14.4 Modifications of the exoskeleton.
The Exoskeleton
• Growth accompanied by ecdysis
(figure 14.5)
1. Enzymes from hypodermal glands
begin digesting old procuticle (a, b).
2. New procuticle and epicuticle
secreted (c, d).
3. Old exoskeleton splits (e)
4. Calcium carbonate deposition
and/or sclerotization hardens new
exoskeleton (f).
Figure 14.5 Events of ecdysis.
The Hemocoel
• Embryonic blastocoel
• Internal cavity for open
circulatory system
– Fluids bathe internal organs.
– Exchange of nutrients, wastes, and
sometimes gases
• Not a hydrostatic compartment
Metamorphosis
• Radical change in body form and
physiology as an immature (larva)
becomes an adult.
– Reduces competition between adult
and immature stages
Subphylum Trilobitomorpha
• Dominant life form from Cambrian
period (600 mya) to Carboniferous
period (345 mya)
• Substrate feeders
• Three tagmata: head, thorax, and
pygidium
• Three longitudinal sections
• Biramous appendages
Figure 14.6 Subphylum Trilobitomorpha (Saukia
sp).
Subphylum Chelicerata
• Spiders, mites, ticks, horseshoe crabs
• Two tagmata
– Prosoma
• Eyes
• Chelicerae
– Often chelate
– Usually feeding appendages
• Pedipalps
– Sensory, feeding, locomotion, reproduction
• Walking legs
– Opisthosoma
• Digestive, reproductive, excretory, and
respiratory organs
Class Meristomata
• Subclasses
Figure 14.7 A eurypterid, Euripterus
remipes.
– Eurypterida
• Extinct giant water
scorpions
(figure 14.7)
Class Meristomata
– Subclass
Xiphosura
• Horseshoe crabs
– Limulus (Atlantic
Ocean and Gulf
of Mexico)
– Book gills
» Gas exchange
between
blood and
water
– Reproduction
» Dioecious
» External
fertilization
Figure 14.8a Limulus
polyphemus.
Figure 14.8b Ventral view of Limulus.
Class Arachnida
• Spiders, mites, ticks, scorpions
• Arose from ancient euryptrids
• Very early terrestrial groups
– 280-400 mya
– Exoskeleton was preadaptation for
water conservation.
Form and Function
• Carnivores
– Chelicerae to hold prey or as fangs
– Gut
• Foregut
– Cuticular
– Pumping stomach
• Hindgut
– Cuticular
– Water reabsorption
• Midgut
– Noncuticular
– Secretion and absorption
Form and Function
• Excretion
– Coxal glands
• Paired sacs bathed in blood of body sinuses
• Homologous to nephridia
• Excretory pores at base of posterior
appendages
– Malpighian tubules
• Blind ending diverticula of gut tract
• Empty via digestive tract
– Uric acid
Form and Function
• Gas Exchange
– Book lungs
• Paired ventral invaginations of body wall
• Gas exchange between air and blood
across book lung lamellae
– Tracheae
• Branched, chitin-lined tubes
• Open at spiracles along abdomen
Figure 14.9 An arachnid book lung.
Form and Function
• Circulation
– Open with dorsal contractile vessel
– Pumps blood into tissue spaces of
hemocoel
– Returns to dorsal vessel via ostia
• Nervous system
– Ventral with fusion of ganglia
Form and Function
• Senses
– Mechanoreceptors
• Modifications of
exoskeleton
• Sensilla respond to
displacement.
– Chemical sense
• Pores in exoskeleton
– Vision
• Eyes detect
movement and
changes in light
intensity.
Figure 14.10 An arthropod seta
(a) and an eye (ocellus) (b).
Form and Function
• Reproduction
– Dioecious
– Indirect sperm transfer
• Male deposits spermatophores, which are
transferred to the female.
– Courtship rituals common
– Copulation occurs in spiders via
modified pedipalp of male.
• Development
– Direct
Order Scorpionida
• Prosoma
– Shieldlike carapace
• Opisthosoma
– Preabdomen
– Postabdomen (“tail” with sting)
• Courtship prior to mating
• Oviparous, ovoviviparous, or
viviparous
Figure 14.11 (a) Hardrurus
arizonensis (b) External anatomy.
(a)
(b)
Order Araneae
• Spiders
• Prosoma
– Chelicerae with poison glands and
fangs
– Pedipalps leglike
• Sperm transfer in males
– 6-8 eyes
• Opisthosoma
– Connected to prosoma via pedicel
– Swollen or elongate
– Visceral functions and spinnerets
Figure 14.12 External structure of Argiope.
Figure 14.13 Prosoma of a spiderling.
Order Araneae
• Silk
– Protein
– Repeating sequence of glycine and
alanine
– Beta sheet
– Stored as gel prior to spinning
– Chemical modification when forced
through spinnerets
• Webs, line retreats, safety lines,
wrapping eggs, dispersal of young
(ballooning)
Figure 14.14
Members of
the family
Araneidae are
the orb
weavers.
Order Araneae
• Feeding
– Insects and other arthropods
– Hunt or capture in webs
– Paralyze prey
• May wrap in silk
– Inject enzymes into prey body wall
• Two spiders are venomous to
humans.
Figure 14.15 (a) Black widow spiders (Lactrodectus
mactans) has a neurotoxic venom. (b) Brown recluse
spiders (Loxosceles reclusa) have a histolytic venom.
(b)
(a)
Order Araneae
• Reproduction
– Complex behaviors
• Chemical, tactile, and visual signals
– Male’s pedipalps enlarged into
embolus
• Male deposits sperm on web and
collects with pedipalps.
• Transfers sperm to female during mating
– Female deposits eggs in silk case.
• In webbing, a retreat, or carries with her
Order Opiliones
Figure 14.16 Order Opiliones
(Leiobunum sp).
• Harvestmen or
daddy longlegs
• Prosoma broadly
joins
opisthosoma
• Legs long and
slender
• Omnivores
• External and
internal digestion
Order Acarina
• Mites
Figure 14.17
– Prosoma and
opisthosoma fused
and covered by
single carapace
– 1mm or less
– Free-living
• Herbivores or
scavengers
– Many pest species
– Ectoparasites
• Chigger
(Trombicula)
• Follicle mite
(Demodex)
Dermatophagoides farinae is
common in homes and grain
storage areas.
Order Acarina
• Ticks
– Ectoparasites in all life stages
– Up to 3cm
– Females lay eggs after engorging
with blood.
– Important in disease transmission
• Rocky Mountain spotted fever
• Lyme disease
Figure 11.18 Ixodes scapularis transmits the bacteria
that causes Lyme disease.
Class Pycnogonida
(Subphylum
Cheliceriformes?)
• Sea spiders
• Marine
• Feed on cnidarian
polyps
• Dioecious
• Molecular,
developmental, and
morphological
characters are being
used to reevaluate
taxonomic status.
Figure 14.19 Class Pycnogonida
Subphylum Crustacea
• Crayfish, shrimp, lobsters, crabs,
copepods cladocerans and others
• Almost all are aquatic
– Terrestrial isopods and crabs are
exceptions.
• Two pairs of antennae
• Biramous appendages (figure
14.20)
Figure 14.20 Crustacean body form. (a) External
anatomy. (b) Biramous appendages.
Class Malacostraca
• Crabs, lobsters, crayfish, shrimp,
krill, amphipods, isopods
• Order Decapoda
– Largest order
– Shrimp, crayfish, lobsters, crabs
Class Malacostraca
• Crayfish external structure
– Cephalothorax
• Fusion of head and thorax
• Covered dorsally and laterally by carapace
• Sensory, feeding, locomotion
– Abdomen
• Muscular “tail” in crayfish
• Locomotor and visceral functions in others
– Paired appendages
• Serially homologous (derived from a common
ancestral pattern)
Figure 14.22 External structure of a male crayfish.
Figure 14.23 Serial homology of crayfish appendages.
Class Malacostraca
• Crayfish internal structure
– Digestive system
• Complete with foregut, midgut, and hindgut
– Respiratory system
• Gills attach at base of cephalothoracic
appendages.
• Lie within gill chamber between carapace and
lateral body wall
• Second maxilla circulates water.
– Circulation
• Open
• Dorsal heart and major arteries
• Blood enters hemocoel, and gills before returning
to pericardial sinus around heart.
Figure 14.24
Internal
structure of a
crayfish.
Class Malacostraca
• Ventral nervous system
– Cephalization and centralization
– Supraesophageal and subesophageal ganglia
process sensory information and control head
appendages.
– Segmental ganglia
• Sensory structures
–
–
–
–
–
–
Antennae
Compound eyes
Statocysts
Chemoreceptors
Proprioceptors
Tactile setae
Class Malacostraca
• Endocrine system
– Ecdysis, sex determination, color
change
• X-organs
– Neurosecretory tissues in eyestalks
– Molt-inhibiting hormone
» Target Y-organ
• Y-organs
– Base of maxillae
– Releases ecdysone when molt inhibiting
hormone is not present and ecdysis occurs
– Androgenic glands (males)
• Promotes development of testes and male
characteristics
Class Malacostraca
• Excretion
– Antennal (green) glands in crayfish
– Maxillary glands in others
– Homologous to coxal glands of
arachnids
• Reproduction
– Dioecious
– Mating after female molts
• Fertilized eggs attach to female’s pleopods
• Others have planktonic larvae
Figure 14.25
(a) Nauplius larva of a
barnacle. (b) Zoea
larvae of a crab.
(a)
(b)
Order Isopoda
• “Pillbugs”
• Aquatic and
terrestrial
• Dorsoventrally
flattened
Figure 14.26a Order Isopoda.
Order Amphipoda
• Laterally
compressed
• Crawl or swim
on sides
• Beach-hoppers
modified for
jumping
Figure 14.26b Order
Amphipoda.
Class Branchiopoda
• Fairy shrimp
– Temporary ponds
• Brine shrimp
– Great Salt Lake
• Cladocera
– Freshwater water
fleas
– Large carapace
– Parthenogenesis
common
• Flattened, leaflike
appendages
Figure 14.27 Order Cladocera.
Class Maxillopoda
• Subclass
Copepoda
– Most abundant
crustaceans
– Important in
marine and
freshwater food
webs
– First antennae
modified for
swimming
Figure 14.1 Subclass
Copepoda.
Class Maxillopoda
• Subclass Thecostracea,
Infraclass Cirripedia
– Barnacles
– Marine
– Monoecious
• Nauplius and cypris larvae
• Cypris larva settles and metamorphoses
into sessile adult.
– Some parasites
Figure 14.28 Class Maxillopoda,
Infraclass Cirripedia.
(a) Internal structure of an
acorn barnacle. (b) A stalked
barnacle (Lepas).
Further Phylogenetic
Considerations
• Diverse body forms and lifestyles of
Arthropoda arose from single
ancestor.
• Crustaceans very successful in
aquatic habitats
• Chelicerata
– First terrestrial arthropods
– Account for evolution of many water
conserving features of the phylum
• Exoskeletal, excretory, and respiratory
adaptations