Transcript Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Arthropods CHAPTER 13 19-1

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Arthropods
CHAPTER 13
19-1
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Characteristics
Arthropodization
• Soft cuticle of the arthropod ancestors was stiffened
by deposition of protein and chitin
• Joints had to provide flexibility
• Sequence of molts was necessary to allow for growth
• Molting required hormonal control
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Characteristics
Relationships among arthropod subgroups
• Centipedes, millipedes are placed in subphylum
Myriapoda
• Insects are placed in subphylum Hexapoda
• Spiders, ticks, horseshoe crabs and their relatives form
subphylum Chelicerata
• Lobsters, crabs, barnacles, and others form subphylum
Crustacea
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19-4
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Great Diversity and Abundance of Arthropods
• Segmentation and Appendages for Efficient
Locomotion
– Appendages often highly specialized for division of labor
– Limb segments are hollow levers with internal striated
muscles
– Appendages may function in sensing, food handling,
walking, or swimming
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Great Diversity and Abundance of Arthropods
• Air Piped Directly to Cells
– Terrestrial arthropods
• Use an efficient tracheal system for oxygen transport
– Aquatic arthropods
• Respire via various forms of gills
• Highly Developed Sensory Organs
– Eyes vary from simple light sensitive ocelli to a compound
mosaic eye
– Other sensory structures for touch, smell, hearing,
balancing, and chemical reception
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Great Diversity and Abundance of Arthropods
• Complex Behavior Patterns
– Arthropods surpass most other invertebrates in complex
and organized activities
– Most behavior is innate but some is learned
• Use of Diverse Resources through Metamorphosis
– Many arthropods undergo metamorphic changes leading
to different larval and adult stages
– Larvae and adults feed on different organisms and occupy
different habitats
• Avoid competition
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Subphylum Trilobita
History of an Ancient Group
• Trilobites arose before the Cambrian, flourished, and
then became extinct 200 million years ago
• Trilobed body shape due to a pair of longitudinal
grooves
• Bottom dwellers and probably were scavengers
• Ranging from 2 to 67 centimeters long
• Could roll up like pill bugs
• Exoskeleton contained chitin strengthened by calcium
carbonate
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19-9
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Subphylum Chelicerata
Characteristics
• Chelicerates have six pairs of cephalothoracic
appendages including chelicerae, pedipalps and four
pair of legs
• Lack mandibles and antennae
• Most suck liquid food from prey
19-10
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Subphylum Chelicerata
Class Merostomata: Subclass Eurypterida
• Eurypterids (giant water scorpions) were the largest of all
fossil arthropods
– 3 m in length
• Fossils date from Ordovician to Permian periods
• Resemble both marine horseshoe crabs and terrestrial
scorpions
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Subphylum Chelicerata
Class Merostomata: Subclass Xiphosurida, Horseshoe
Crabs
• Modern horseshoe crab nearly unchanged from
ancestors in the Triassic period
• Most live in shallow water
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19-13
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Subphylum Chelicerata
Class Pycnogonida: Sea Spiders
• All have small, thin bodies
• Males may have a pair of legs (ovigers) to carry
developing eggs
• Many have chelicerae and palps
• Mouth, at the tip of a proboscis, sucks juices from
cnidarians and soft-bodied animals
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19-15
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Subphylum Chelicerata
Class Arachnida
• Most are free living and more common in warm, dry
regions
Structures
• Divided into two tagmata: a cephalothorax and an
abdomen
• No antenna
• Most are predaceous and have claws, fangs, poison
glands, or stingers
• Sucking mouthparts ingest fluids and soft tissues
from bodies of their prey
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19-17
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Subphylum Chelicerata
• In spiders and insects, Malpighian tubules serve as excretory
structures
• Many spiders have coxal glands, modified nephridia, at the
base of legs
– Most spiders have eight simple eyes, each with a lens,
optic rods, and a retina
• Detect movement and may form images
• Sensory setae detect air currents, web vibrations, and
other stimuli
• Spider’s vision usually poor
• Awareness of environment depends largely on cuticular
mechanoreceptors such as sensory setae
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19-19
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Subphylum Chelicerata
• Are spiders really dangerous?
–
–
–
–
Most people fear spiders without good reason
Spiders are allies of humans in our battle with insects
American tarantulas rarely bite, and bite is not dangerous
Species of black widow spiders are dangerous
• Venom is neurotoxic
– Brown recluse spider
• Hemolytic venom that destroys tissue around the bite
– Some Australian and South American spiders are the most
dangerous and aggressive
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19-21
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Subphylum Chelicerata
Order Scorpionida: Scorpions
• More common in tropical and subtropical zones but
occur in temperate areas
• Nocturnal and feed largely on insects and spiders
• Long, slender tail of five segments that ends in a
stinging apparatus
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19-23
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Subphylum Chelicerata
Order Opiliones: Harvestmen
• Harvestmen or daddy longlegs
• Common, particularly in tropical regions
• Unlike spiders, abdomen and cephalothorax join
broadly
• Can lose most of their eight long legs without ill
effect
• Chelicerae are pincerlike
• Mostly scavengers
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Subphylum Chelicerata
Order Acari: Ticks and Mites
• Medically and economically the most important
arachnids
• Both aquatic and terrestrial
– Inhabit deserts, polar areas, and hot springs
• Most mites are less than 1 millimeter long
• Ticks may range up to 2 cm
• Complete fusion of cephalothorax and abdomen
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19-26
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Subphylum Chelicerata
• House dust mites
– Free-living and often cause allergies
• Spider mites
– One of many important agricultural pest mites that suck
out plant nutrients
• Chiggers
– Larval Trombicula mites
– Feed on dermal tissues and cause skin irritation
• Hair follicle mite Demodex
– Harmless but other species cause mange in domestic
animals
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19-28
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Subphylum Myriapoda
Characteristics
• Myriopods include
– Chilopoda (centipedes)
– Diplopoda (millipedes)
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Subphylum Myriapoda
Class Chilopoda
Natural History
• Centipedes
• Found under logs, bark and stones
• Carnivorous, eating earthworms, cockroaches, and
other insects
• House centipede has 15 pairs of long legs
– Common in bathrooms and damp cellars
• Most harmless to humans
– Few large, tropical centipedes are dangerous
• Approximately 3,000 species worldwide
19-30
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19-31
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Subphylum Myriapoda
Class Diplopoda
Natural History
• Millipedes
• Less active than centipedes
– Walk with graceful rather than wriggling motion
• Most eat decayed plants but a few eat living plant
tissue
• Most are slow moving and roll into a coil for defense
• Some secrete toxic or repellant fluids from special
repugnatorial glands on side of body
• More than 10,000 species of worldwide
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19-33
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Phylogeny and Adaptive Diversification
Classification
• Subphylum Trilobita
• Subphylum Chelicerata
– Class Merostomata
– Class Pycnogonida
– Class Arachnida
• Subphylum Myriapoda
–Class Diplopoda
–Class Chilopoda
»Subphylum Crustacea
»Subphylum Hexapoda
19-34
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Subphylum Crustacea
General Nature of a Crustacean
• Main distinguishing characteristic of crustaceans
– Two pairs of antennae
• Head also has a pair of mandibles and 2 pairs of
maxillae
• One pair of appendages on each of the additional
segments
– Some segments may lack appendages
– All appendages, except perhaps first antennae, are biramous
• Tagmata are usually head, thorax, and abdomen
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20-36
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Subphylum Crustacea
• Most crustaceans have a larva unlike the adult in form,
and undergo metamorphosis
• The nauplius is a common larval form with uniramous
first antennae, and biramous second antennae and
mandibles that all aid in swimming
– Appendages and somites are added in a series of
molts
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20-38
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Subphylum Crustacea
• Feeding Habits
– Same fundamental mouthparts are adapted to a wide
array of feeding habits
– Suspension feeders generate water currents in order to
feed on plankton, detritus ,and bacteria
– Predators consume larvae, worms, crustaceans, snails, and
fishes
– Scavengers eat dead animal and plant matter
– Crayfishes have a two-part stomach
• Gastric mill grinds up food in 1st compartment
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Brief Survey of Crustaceans
Class Branchiopoda
• Over 10,000 species, 4 orders
– Order Anostraca, includes fairy shrimp and brine
shrimp
• Lack a carapace
– Order Notostraca, includes tadpole shrimp
• Carapace forms a large dorsal shield
– Order Conchostraca, includes clam shrimp
• Enclosed by a bivalved carapace
– Order Cladocera, includes water fleas
• Carapace encloses the body but not the head
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20-41
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Brief Survey of Crustaceans
• In all flattened, leaf-like legs serve as respiratory
organs, assist in suspension feeding, and, locomotion
• Most are freshwater
• Important component of freshwater zooplankton
• May reproduce by parthenogenesis to rapidly boost
summer populations and then by sexual
reproduction with the onset of unfavorable
conditions
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20-43
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Brief Survey of Crustaceans
Class Maxillopoda
• General body plan
– Five cephalic, six thoracic and four abdominal somites plus
a telson
• No appendages on abdomen
• When present, the eye is unique in structure and
called a maxillopodan eye
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Brief Survey of Crustaceans
Class Ostracoda
• Enclosed in a bivalve carapace
• Most are benthic or climb onto plants, but some are
planktonic, parasitic, or burrowing
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Brief Survey of Crustaceans
Subclass Copepoda
• Third in numbers of species
• Lack a carapace and retain simple, median, nauplius
eye in the adult
• Single pair of uniramous maxillipeds and four pairs of
flattened, biramous, thoracic swimming appendages
• Parasitic forms highly modified and reduced
– Often unrecognizable as arthropods
• Free-living copepods may be the dominant consumer
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Brief Survey of Crustaceans
Subclass Branchiura
•
•
•
•
Lack gills
Most are ectoparasites of marine and freshwater fish
5–10 mm long
Broad, shield-like carapace, compound eyes, four
biramous thoracic swimming appendages, and a short
unsegmented abdomen
• Second maxillae are modified as suction cups to
attach to host fish
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20-48
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Brief Survey of Crustaceans
Subclass Pentastomida
• Tongue worms
• Consist of about 90 species of parasites of vertebrate
respiratory systems
• Most infect reptile lungs, a few infect air sacs of birds
or mammals
• More common in tropical regions extending out to
North America, Europe, and Australia
• Range from 1 to 13 cm in length
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20-50
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Brief Survey of Crustaceans
Subclass Cirripedia
• Includes barnacles in order Thoracica and three orders
of burrowing or parasitic forms
• Adults are sessile and attach directly (acorn barnacles)
or by a stalk (goose barnacles)
• Carapace surrounds body and secretes a set of
calcareous plates
• Head is reduced, abdomen is absent, and thoracic
legs are long with hairlike setae
• Jointed cirri bear setae and extend from the plates to
feed on small particles
• In barnacles in intertidal zones, plates close to protect
against dessication
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20-52
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Brief Survey of Crustaceans
Class Malacostraca
• Largest and most diverse class of Crustacea with over
20,000 species
• Contains three subclasses, 14 orders, and many
suborders
Order Isopoda
• Only truly terrestrial crustaceans
• Also have marine and freshwater forms
• Dorsoventrally flattened, lack a carapace, and have
sessile compound eyes
• Common land forms include sow bugs and pill bugs
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20-54
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Brief Survey of Crustaceans
Order Amphipoda
• Amphipods resemble isopods
– Lack a carapace, have sessile compound eyes, and one pair
of maxillipeds
• However, they are compressed laterally, and gills are
in the thoracic region
• Abdominal and thoracic limbs are grouped for
jumping and swimming
• Many are marine, others are beach-dwelling,
freshwater, or parasitic
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Brief Survey of Crustaceans
Order Euphausiacea
•
•
•
•
•
Approximately 90 species
Includes important ocean plankton called krill
Carapace does not completely enclose gills
Lack maxillipeds and all limbs have exopods
Most are bioluminescent with a light-producing organ
called a photophore
• Form a major component of the diet of baleen whales
and of many fishes
• Eggs hatch as nauplii
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20-58
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Brief Survey of Crustaceans
Order Decapoda
• 5 pairs of walking legs and 3 pairs of maxillipeds
• In crabs, first pair of walking legs form pincers
• Range from a few millimeters to the Japanese crab with a
4 m leg-span
• Approximately 18,000 species
• Includes crayfishes, lobsters, crabs, and true shrimp
• Crabs have a broader cephalothorax and reduced
abdomen, compared to crayfish or lobsters
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20-60
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21-61
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Diversity and Characteristics
Subphylum Hexapoda
• Members named for the presence of six legs
– All legs are uniramous
• Have 3 tagmata
– Head
– Thorax
– Abdomen
• Appendages attach to head and thorax
• Two classes within Hexapoda
– Entognatha
– Insecta
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Diversity and Characteristics
• Characteristics of Insecta
– Enormous class whose members have ectognathous
mouthparts, however, bases of mouthparts lie outside the
head capsule
– Pterogotes: winged insects
– Apterogotes: wingless insects
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Class Insecta
• Distribution
– Found in nearly all habitats except the sea
– Common in freshwater, brackish water, and salt marshes
– Abundant in soils, forest canopies, and can be found in
deserts and wastelands
– Most animals and plants have insects as parasites externally
and internally
• Adaptive Traits
– Flight and small size makes insects widely distributed
– Well-protected eggs withstand rigorous conditions and are
readily dispersed
– Wide variety of structural and behavioral adaptations gains
them access to every possible niche
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Class Insecta
• Head
– Usually equipped with pair of large compound
eyes
– One pair of antennae varies greatly in
• Function in touch, taste, hearing
– Mouthparts consist
•
•
•
•
Labrum
Pair of mandibles and maxillae,
Labium
Hypopharynx
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Class Insecta
• Thorax
– Consists of the prothorax, mesothorax and metathorax
– Each section has a pair of legs
• Wings
– If two pairs present: located on the mesothorax and
metathorax
– Consist of a double membrane
– Veins serve to strengthen the wing
• Vein pattern used to identify insect taxa
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Class Insecta
• Legs
– Walking legs end in terminal pads and claws
– Hindlegs of grasshoppers and crickets are enlarged for
jumping
– Mole crickets have front legs adapted for burrowing in
ground
– Forelegs of praying mantis allow it to grasp prey
– Honeybees have leg adaptations for collecting pollen
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Class Insecta
– Most feed on plant tissues or juices and are herbivorous or
phytophagous
– Many caterpillars are specialized to eat only certain species
of plants
– Some ants and termites cultivate fungus gardens for food
– Many beetles and other insect larvae eat dead animals and
are saprophagous
– Some species are predaceous on other insects or other
animals
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Class Insecta
– Many species are parasitic as adults and/or larvae
– Many parasitic insects, in turn, have parasites, a condition
called hyperparasitism
– Parasitoids live inside a host and eventually kill the host
• Important in pest control
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Class Insecta
• Gas Exchange
– Terrestrial animals are faced with the dilemma of
exchanging gases while preventing water loss
– Tracheal system
• Network of thin-walled tubes that branch throughout the insect
body
• Evolved independently of that of other arthropod groups
– Spiracles open to the tracheal trunks
• 2 spiracles on thorax and 7–8 on abdomen
– Valve on the spiracle
• Reduces on water loss and may serve as a dust filter
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Class Insecta
• Sense Organs
– Many insects have keen sensory perception
– Most sense organs are microscopic and located in body
wall
– Different organs respond to mechanical, auditory,
chemical, visual, and other stimuli
– Mechanoreception
• Touch, pressure, vibration, etc. are detected by sensilla
– May be a single hair-like seta or a complex organ
– Distributed widely over antennae, legs, and body
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Class Insecta
– Chemoreception
• Usually bundles of sensory cell processes located in
sensory pits
• May occur on mouthparts, antennae, and legs
• Some insects can detect odors several kilometers away
• Feeding, mating, habitat selection, and host-parasite
relationships are mediated through chemical senses
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Class Insecta
– Visual Reception
• 2 types of eyes: simple and compound
• Honeybee studies indicate that ocelli monitor light
intensity but do not form images
• Compound eyes may contain thousands of ommatidia
– Ommatidia structure similar to that of crustaceans
• Insects can see simultaneously in almost all directions
– Image is myopic and fuzzy
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Class Insecta
• Reproduction
– Parthenogenesis occurs predominantly in some Hemiptera
and Hymenoptera
– Sexual reproduction is the norm
– Sexes are separate
– Sexual Attraction
• Female moths secrete a pheromone to attract males
from a great distance
• Fireflies use flashes of light to detect mates
• Some insects use sounds, color signals, and other
courtship behaviors
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Class Insecta
• Metamorphosis and Growth
– Various forms of metamorphosis produce degrees of
change among different insect groups
– Most insects change form after hatching from egg
– Each stage between molts is called an instar
– Insects develop wings during the last stage
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Class Insecta
– Defense
• Protective coloration, warning coloration, and mimicry
are protective adaptations
• Stink bugs and others have repulsive odors and tastes
• Some insects are aggressive (e.g., bees and ants)
• The monarch caterpillar incorporates a poisonous
substance from its food plant, milkweed
• The bombardier beetle can spray an attacking enemy
with irritating chemicals
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Class Insecta
– Pheromones
• Chemicals secreted by one individual to affect the
behavior of another individual
• Attract the opposite sex, trigger aggregation, fend off
aggression, and mark trails
• Bees, wasps, and ants can recognize nestmates and
signal an alarm if strangers enter the nest
• Can be used to trap insects to monitor populations
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Class Insecta
– Sound Production and Reception
• Sounds are used as warning devices, advertisement of
territory, and courtship songs.
• Crickets chirp for courtship and aggression
• Male cicada vibrates paired membranes on abdomen to
attract females
– Tactile Communication
• Involves tapping, stroking, grasping, and antennae
touching
• Some beetles, flies and springtails use bioluminescence
• Some female fireflies mimic another species’ flash pattern
to attract males and then eat them
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Class Insecta
– Social Behavior
• Some social communities are temporary and
uncoordinated
• Others are highly organized and depend on chemical
and tactile communication
• Caste differentiation is common in most organized
social groups
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Insects and Human Welfare
• Beneficial Insects
– Insects produce honey, beeswax, silk and shellac
– Of more economic importance, bees pollinate $10
billion worth of food crops in the U.S. annually
– Pollinating insects and flowering plants are tightly
co-evolved
– Predaceous and parasitoid insects are vital in
controlling many pest insect populations
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Insects and Human Welfare
– Dead animals rapidly consumed by fly maggots
– Insects are critical components of most food
chains and an important food source for many fish
and birds
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Insects and Human Welfare
• Harmful Insects
– Harmful insects eat and destroy plants and fruits
– Nearly every cultivated crop has several insect
pests
• Requires substantial money for insect control
– Bark beetles, spruce budworms, the gypsy moth
and others are serious forest pests.
– Insects also destroy food, clothing, and property
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Insects and Human Welfare
– Medically important insects include vectors for
disease agents
– 10% of all arthropod species are parasites or
“micropredators”
– Warble and bot flies attack humans and domestic
livestock
– Malaria is carried by Anopheles mosquitos
• Most common major world disease
– Yellow fever and lymphatic filariasis are also
mosquito-borne
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Insects and Human Welfare
– Fleas carry plague, a disease that changed human
history in the Middle Ages
– Lice carry typhus fever
– The tsetse fly carries African sleeping sickness
– The newest viral plague to hit North America, the
West Nile virus, is carried by mosquitos
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