Classification- Phylum Arthropoda
Chapter 19
Subphylum Trilobita (extinct)
Subphylum Chelicerata
Class Arachnida
Order Araneae
Order Scorpiones
Order Opiliones (Daddy Longlegs)
Order Acari (Ticks and Mites)
Subphylum Myriapoda
Class Diplopoda
Class Chilopoda
Chapter 20
Subphylum Crustacea
Chapter 21
Subphylum Hexapoda
CHAPTER 19
Trilobites,
Chelicerates, and
Myriapods
19-2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
19-3
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Characteristics
Anthropodization





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
Hydrostatic skeleton function was lost


19-4
Coelom regressed and was replaced by open
sinuses
Motile cilia were lost
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Characteristics
Phylum Arthropoda



19-5
Contains over 3/4 of all known species
Coelomate protostomes with well-developed
organ systems
Segmented
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Characteristics





19-6
Sizes range from the Japanese crab (four meters in
leg span) to the 0.1 mm long follicle mite
Abundance and wide ecological distribution makes
them the most diverse animal group
Some are agents of disease and compete with
humans for food
Others are beneficial
All modes of feeding occur among arthropods;
carnivores, omnivores, herbivorous (most),
decomposers, scavengers, parasites, etc.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Japanese Spider Crap
Follicle Mite
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Characteristics
Relationships among arthropod subgroups






Divided into subphyla based on relationships
between subgroups
Groupings among subphyla based on
molecular data
Centipedes, millipedes are placed into
subphylum Myriapoda
Insects are placed in subphylum Hexapoda
Spiders, and ticks form subphylum Chelicerata
Lobsters, crabs, barnacles, and others form
subphylum Crustacea
19-8
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2 Important Parts
in Arthropods:
Appendages and
Mouthparts
Uniramous: single branched
Biramous: 2 branches
Chelicerae: pointed appendages to grasp food
Mandible: chewing appendage
19-9
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
19-10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Great Diversity and Abundance of Arthropods
WHY HAVE ARTHROPODS SURVIVED…
 1. Versatile Exoskeleton





19-11
Cuticle is highly protective and jointed, providing
mobility
Consists of inner thick procuticle and outer thin
epicuticle
Procuticle has an exocuticle secreted before a molt
and an endocuticle secreted after molting
Both layers of procuticle contain chitin bound with
protein
Procuticle is lightweight, flexible, and protects
against dehydration
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
19-12
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Great Diversity and Abundance of Arthropods


Cuticle is further hardened by tanning
Ecdysis, or molting


19-13
Process of shedding outer covering and growing a new,
larger one
Arthropods typically molt four to seven times
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Survival of Arthropods

2. 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
3. Use of Diverse Resources through
Metamorphosis


19-14
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Survival of Arthropods

4. Air Piped Directly to Cells



Terrestrial arthropods
 Use an efficient tracheal system for oxygen
transport directly to tissues
Aquatic arthropods
 Respire via various forms of gills
5. Highly Developed Sensory Organs


19-15
Eyes vary from simple light sensitive ocelli to a
compound mosaic eye
Other sensory structures for touch, smell,
hearing, balancing, and chemical reception
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Early Arthropod fossils: Trilobites and Eurypterid
19-16
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata
Characteristics




Chelicerates have six pairs of
cephalothoracic appendages including
chelicerae (eating), pedipalps (mating) and
four pair of legs
Lack mandibles and antennae
Most suck liquid food from prey
Example: spiders, horseshoe crabs, sea
spiders, ticks, scorpions
19-17
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Spiders
Sea
Spiders
Horseshoe Crabs
19-18
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Horseshoe Crab: Illustrating 6 pairs of appendages
19-19
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Sea spiders: Illustrating
6 sets of appendages
19-20
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata
Class Arachnida
Great diversity
 Most are free living and more common in
warm, dry regions
Structures
 Divided into two body parts: a cephalothorax
and an abdomen
 Cephalothorax bears a pair of chelicerae, a
pair of pedipalps, and 4 pairs of walking legs
 No antenna and mandibles
 Example: Spiders, Ticks, and Scorpions

19-21
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata




Most are predaceous and have claws, fangs,
poison glands, or stingers
Sucking mouthparts ingest fluids and soft
tissues from bodies of their prey
Spiders have spinning glands
Pedipalps of males are modified, sometimes
elaborately, for sperm transfer
19-22
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata





Over 80,000 species have been
described
Most harmless to humans and provide
essential control of injurious insects
Some spiders are venomous and can
cause pain or death in humans
Ticks may carry human diseases
Mites can be crop pests
19-23
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata
Order Araneae: Spiders







Approximately 40,000 species
Body consists of an unsegmented
cephalothorax and abdomen joined by a
slender pedicel
Anterior appendages are a pair of chelicerae
with terminal fangs
Pair of pedipalps have sensory functions and
are used by males to transfer sperm
Basal parts of pedipalps used to handle food
Four pairs of walking legs terminate in claws
All are predaceous, mostly on insects
19-24
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
External Anatomy of Jumping Spider
19-25
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata




Injected venom liquefies and digests the tissues which
is sucked into spider’s stomach
RESPIRATORY SYSTEM
Breathe by book lungs and/or trachea
Book lungs unique to spiders






Parallel air pockets extend into blood-filled chamber
Air enters chamber through a slit in body wall
Trachea system
 Transports air directly to tissues/blood through an opening
called a spiracle
Excretory System
In spiders and insects, Malpighian tubules serve as
excretory structures
Rectal glands reabsorb water. Conserves water and
allows the organisms to live in dry environments
19-26
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Internal Anatomy of a Spider
19-27
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata

Sensory Systems
 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
 Vision is poor, rely on mechanoreceptors
(stimuli)
19-28
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata

Web-Spinning Habits
Spinning silk critical ability for spiders
 Two or three pairs of spinnerets contain
microscopic tubes that run to silk glands
 Liquid scleroprotein secretion hardens as
it is extruded from spinnerets
 Silk threads are very strong and will
stretch considerably before breaking
 Silk is used for orb webs, lining burrows,
forming egg sacs, and wrapping prey

19-29
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
19-30
Grasshopper snared in Golden Garden Spider silk.
If the spider is not hungry, it will save the live prey for later.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fisher Spider: Catches prey, paralyzes them,
pumps in digestive enzymes,
then sucks out predigested contents.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata

Reproduction





19-32
Before mating, male stores sperm in pedipalps
Mating involves inserting pedipalps into the
female genital openings
A courtship ritual is often required before the
female will allow mating
Eggs may develop in a cocoon in the web or may
be carried by female
Young hatch in about two weeks and may molt
before leaving the egg cocoon
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Wolf spider with egg sack
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Black Widow with egg sack
19-33
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata

Are spiders really dangerous?






19-34
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Tarantula: Not Dangerous. Bite similar to Bee Sting
Bite when threatened or defending eggs/young.
19-35
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A: Black Widow displaying Red Hourglass
B: Brown Recluse Spider displaying violin marking on cephalothorax
19-36
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata
Order Scorpionida: Scorpions





More common in tropical and subtropical
zones but occur in temperate areas
Approximately 1,400 species worldwide
Nocturnal and feed largely on insects and
spiders
Sand-dwellers locate prey by detecting
surface waves with leg sensillae
Appendages attached to cephalothorax



Pair of medial eyes and 2–5 lateral eyes
Preabdomen has 7 segments
Postabdomen has long, slender tail of five
segments that ends in a stinging apparatus
19-37
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Emperor Scorpion with young.
Young stay with mother until their first molt.
19-38
Harvestmen: Order Opiliones
AKA- Daddy Longlegs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata




Under the abdomen are comblike pectines
 Explore the ground and aid in sex
recognition
Stinger on last segment has venom that
varies from mildly painful to dangerous
Ovoviviparous or viviparous and produce
from 6 to 90 young
Perform complex mating dances
 In some species the male stings the female
on pedipalp or on edge of cephalothorax
19-39
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata
Order Opiliones: Harvestmen







Harvestmen or daddy longlegs
Approximately 5,000 species worldwide
Unlike spiders, abdomen and cephalothorax
join broadly without a narrow pedicel
Can lose most of their eight long legs
without ill effect
Chelicerae are pincerlike
Mostly scavengers
Have 2 eyes, not 8
19-40
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata
Order Acari: Ticks and Mites



Medically and economically the most
important arachnids
About 30,000 species have been described
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
No sign of external segmentation
19-41
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata





Mouthparts on tip of the anterior capitulum
Chelicerae on each side help pierce, tear, or
grip food
Adult mites and ticks possess 4 pairs of legs
Transfer sperm directly or by
spermatophores (packets of sperm)
Egg hatches, releasing a six-legged larva

19-42
Eight-legged nymph stages follow
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Wood Tick
All stages are ectoparasites
19-43
Red Velvet Mite: Trombicula
Only Larvae is ectoparasite
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata

House dust mites


Spider mites


One of many important agricultural pest mites
that suck out plant nutrients
Chiggers



Free-living and often cause allergies
Larval Trombicula mites
Feed on dermal tissues and cause skin irritation
Hair follicle mite Demodex

19-44
Harmless but may cause mild dermatitis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Human Follicle Mite
19-45
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata

Human itch mite


Causes intense itching
Popular in WWII - due to crowded conditions in
which people lived
Human Itch Mite
19-46
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Chelicerata
Ticks:
2nd premier disease vector (after mosquito).
Species include:
Ixodes
Some
carry Lyme disease
Bacterial infection dicovered in 1970, in the city of Lyme,
Conneticut.
Dermacentor
Transmit
Cattle
Rocky Mountain spotted fever
tick
Transmits
Texas cattle fever (Protozoan)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Tick: Carries Texas Cattle Fever
19-48
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Myriapoda
Characteristics

Myriopods (“Many Footed”) include:




Chilopoda (centipedes)
Diplopoda (millipedes)
Use trachea to transport respiratory gases to
all body tissue
Excretion usually by Malpighian tubules
19-49
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
19-50
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Myriapoda
Class Chilopoda





Centipedes
Found under logs, bark and stones
Carnivorous, eating earthworms,
cockroaches, and other insects
Centipedes usually have one pair of legs on
each segment
Most harmless to humans


Few large, tropical centipedes are dangerous
Approximately 3,000 species worldwide
19-51
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Centipede from Amazon, Peru.
19-52
Head of a Centipede
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Myriapoda
Characteristics





Terrestrial and have flattened bodies with up
to 177 segments
Each segment except the one behind the head
and last two
 Bears a pair of jointed legs
Appendages of first body segment form
poison claws
Head has one pair of antennae
Eyes on either side of the head consist of
groups of ocelli
19-53
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Myriapoda
Reproduction



Sexes separate with unpaired gonads and
paired ducts
Some lay eggs and others are viviparous
Young resemble adults and do not undergo
metamorphosis
19-54
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Myriapoda
Class Diplopoda


Millipedes (double footed)
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 glands on side of body
More than 10,000 species of worldwide
19-55
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Tropical millipede.
19-56
Head of a Millipede
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Myriapoda
Characteristics




Cylindrical bodies with 25 to more than
100 segments
Short thorax consists of 4 segments,
each bearing one pair of legs
Each abdominal segment has 2 sets of
legs
Head has 2 clusters of simple eyes and
a pair each of antennae and mandibles
19-57
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subphylum Myriapoda
Reproduction



Appendages of seventh segment specialized
as copulatory organs
After copulation, female lays eggs in a nest
and guards them
Larvae have only one pair of legs per
segment
19-58
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Classification
Classification- Phylum Arthropoda
 Subphylum Trilobita (extinct)
 Subphylum Chelicerata
 Class Arachnida





Order Araneae
Order Scorpiones
Order Opiliones (Daddy Longlegs)
Order Acari (Ticks and Mites)
Subphylum Myriapoda


Class Diplopoda
Class Chilopoda

Subphylum Crustacea

Subphylum Hexapoda
19-59