Arthropods
Arthropods: Most Successful Group Ever!
• Insects cause huge economic losses (but a lot of benefits,
as well) each year
–
–
–
–
–
–
Negatives
Compete for humans for food supplies
Spread serious diseases
Positives
Pollinate flowers
Food, yield drugs and dyes, create silk, honey and beeswax
• They are the dominant group of animals on the earth
today
• The diversity of insects is far greater than all other taxa
combined
• There are an estimated _____ million insects alive for
every human today
Locust Outbreaks in Africa (still today)
• Contain 40-80 million insects per sq. kilometer
• Can cover up to 20% of earth’s surface at peak
times
Phylum Arthropoda
• Arthropods includes spiders, scorpions, ticks, mites,
crustaceans, millipedes, centipedes, insects, and
some smaller groups as well
• There is a rich fossil record extending back to the
mid-______________________ period
Ecological Relationships
• They are found in all environments and
virtually all altitudes and latitudes
• Species are adapted to land and to fresh,
brackish, and marine water
• Most species fly to their favored habitats
• All modes of feeding occur among arthropods
though the majority are ________________
• Nothing else matches their diversity
General Characteristics: Arthropods
Arthropods are invertebrates that have jointed appendages.
There are over a million known species making them the
largest group of animals. Why so diverse and abundant???
Characteristics:
- Jointed
jointed appendage
__________________**
- Bilateral
symmetry (cephalization**)
- Segmented
bodies**
- Exo_________________**
- Coelom and Triploblastic
- Body Systems**
- Complex
behavior patterns**
- Separate sexes (most)
Exoskeleton (made of chitin)
bilateral symmetry
Evolutionary Milestone: _______________
Arthropods have various appendages. They are
differentiated and specialized for walking swimming, flying,
or eating. Typically each segment has a pair of jointed
appendages (may be reduced though). They can also be
equipped with sensory hairs for sensory functions.
Segmented Bodies
The bodies of arthropods are divided into segments similar to
those of segmented worms. However, two things: Unlike
annelids, arthropods have various patterns of segmentation. And
segmentation in these two groups evolved independently!!!
- Some arthropod
have many
segments
- Others have fused
segments or somites
that form body regions
(tagma or tagmata)
Segmented Bodies
Exoskeleton
All arthropods have a hard, outer covering called an
_______________________.
- Covers, supports, and protects the
arthropod, without sacrificing mobility
- Made of CHITIN (tough
polysaccharide) and the protein
resilin
- Many land-dwelling arthropods have
a waxy layer to prevent water loss.
- The exoskeleton cannot grow
as the animal grows, thus
many species molt (or
ecdysis)
Exoskeleton
Cuticle (exoskeletion) consists of:
•Epicuticle: outer, thin layer
•Procuticle: inner, thicker layer that is flexible and prevents
water loss
Divided into two parts:
Exocuticle-secreted before a molt
Endocuticle-secreted after molting
Cuticle may be soft or like a coat of armor.
Other functions: ingrowth for muscle attachment, support
tracheae
• Respiration – marine
www.emc.maricopa.edu
arthropods have GILLS;
land arthropods have a
series of tubes inside
(trachea) and spiracles
(pores) on body surface.
Oxygen pumped directly
to tissues.
www.teleological.org
• Cephalization- have
Dragonfly eyes
large heads, slender
necks, intricate eyes and
other sensory organs,
important for arthropod
success.
Other Body Systems….
• COMPLETE Digestive
System:
– With adapted
mouthparts
– Specialized gut
• Complex Muscular System:
– Exoskeleton for attachment
– Striated muscles for rapid
action
– Smooth muscles for visceral
organs
More Body Systems…..
• Nervous system
– Similar to annelids
– Dorsal brain
– Double nerve cord
connecting ventral ganglia
• Circulatory System
– OPEN system
– Dorsal pumping heart
• Reproduction
– Sexes usually Separate
– Usually Internal
fertilization
Phylum Arthropoda
Subphylum Trilobita
Subphylum Chelicerata
Class Merisomata (horseshoe crabs)
Class Pycnogonida (sea spiders)
Class Arachnida (spiders, mites, ticks, scorpions)
Mandibulata
Subphylum Myriopoda (centipedes, millipedes)
Class Diplopoda (millipedes)
Class Chilopoda (centipedes)
Subphylum Crustacea
Class Branchiopoda (water fleas, sea-monkeys)
Class Ostracoda (seed shrimps)
Class Cirripedia (barnacles)
Class Peracarida (Isopoda, slaters, woodlice)
Class Malacostraca (shrimps, prawns, crabs, lobsters, crayfish, yabbies)
Subphylum Insecta (Hexapoda)
Class Apterygota (wingless insects e.g. earwigs)
Class Pterygota (winged insects)
Taxonomy
• Subphylum Uniramia used to exist
– Recently divided into two subphyla
• Myriapoda
• Hexapoda
Arthropods are classified based on
types of appendages present and
number of tagmata (body regions)
Subphylum Trilobita
• Trilobita arose before the Cambrian, flourished, and
then became extinct 250 million years ago
• They have a trilobed body shape due to a pair of
longitudinal grooves
• They were bottom dwellers and probably were
scavengers
• They ranged from an inch to 20 inches or more and
could roll up like pill bugs
Subphylum Chelicerata
• Include the horseshoe crabs, spiders,
ticks, mites, scorpions, and sea spiders
• Chelicerates have SIX pairs of
appendages including chelicerae,
pedipalps and FOUR pairs of legs (how
classified!)
• They lack mandibles and antennae
• Most suck liquid food from prey
Chelicerata: Class Merostomata
• Includes the modern horeshoe crab; Limulus
polyphemus
• This species is nearly unchanged from its
Cambrian ancestor (Eurypterids; lived 200-500
mya)
• Five species survive today
Class Merostomata: The Horseshoe Crab
• Most live in shallow water (North American
Atlantic coast)
• They have an unsegmented carapace that covers
the body in front of a broad abdomen
• A TELSON or spinelike tail
• Book gills are exposed on some of the abdominal
appendages
• They walk with their walking legs and swim with
abdominal plates
• They feed at NIGHT on worms and small molluscs
• Mating: Male clings to Female’s back
Horseshoe Crabs
Chelicerata: Class Pycnogonid- Sea Spiders
• They vary from a few millimeters to centimeters; all
have small, thin bodies
• Some males use legs to carry developing eggs
• The mouth at the tip of a proboscis, drinks juices
from cnidarians (hydroids) and soft-bodied animals
• They have a greatly reduced abdomen attached to an
elongated cephalothorax (tagmata)
Chelicerata: Class Arachnida-Spiders, etc.
• Consists of a great diversity among scorpions,
mites, ticks, daddy longlegs and others
• Of 80,000 species, most are free living and
more common in warm, dry regions
• Arachnids are divided into a cephalothorax
and abdomen (tagmata)
Order Araneae: JUST Spiders
• About 40,000 species of spiders are known
• The body consists of an unsegmented
cephalothorax and abdomen joined by a
slender pedicel (waistline!)
Order Araneae: The Spiders
• The anterior appendages are a pair of
chelicerae with terminal fangs
• All spiders are Predators, mostly on insects,
which are killed by poison
• The injected __________ liquefies and digests
the tissues which are then sucked into the
spider’s stomach
• Spiders breath by book lungs and/or trachae
Characteristics of the spiders
• Book lungs are found only in the spiders; parallel
air pockets extend into a blood-filled chamber
• Air enters the chamber through a slit in the body wall
• The tracheae system is less extensive than in
insects; it carries air directly to tissues
• Spiracles are openings to the trachea
• Most spiders have ______ simple eyes, each with
a lens, optic rods and a retina
• They detect movement and may for images
• Sensory Setae detect air currents, web vibrations,
and other stimuli
Web-spinning Habits
• Spinning Silk is a critical ability for spiders and
some other arachnids
• Two or three pairs Spinnerets contain
microscopic tubes that run to silk glands
• A liquid protein secretion hardens as it is
extruded from the spinnerets
• Silk threads are very strong and will stretch
considerably before breaking
• Spiders are often camouflaged
or cryptic
Web-spinning Habits
• Jumping spiders (Salticidae) have excellent vision and stalk their prey
• Silk is used for orb webs, lining burrows, forming egg sacs, and wrapping
prey
• Wolf spiders, jumping spiders, and fisher spiders chase and catch their
prey
Spider Diversity
Reproduction in spiders
• ______________ court ____________ before mating
• The male spins a small web, deposits a drop of sperm
on it, and then stores the package in his pedipalp
• Mating involves inserting the pedipalps into the
female genital openings and depositing the
spermatophore
• Sperm are stored in a seminal receptacle for weeks or
months until the eggs are ready
• Eggs may develop in a cocoon in the web or may be
carried by the female
• The young hatch in a few weeks and may molt before
leaving the cocoon
Venomous spiders
• Most are feared for no reason at all!!
• Spiders help to control the populations of insects
• American tarantulas rarely bite and the bite is not
dangerous
• The black widow (Lactrodectus mactans)
however, can be fatal
– The venom is neurotoxic (attacks nervous system)
• The brown recluse spider, Loxosceles recluse,
has hemolytic venom that destroys tissue
around the bite
• Some Australian and South American Spiders are
the most dangerous and aggressive
Black Widow
Brown Recluse
Order Scorpionida: Scorpions
• More common in tropical and subtropical (such
as Florida!) zones but do occur in temperate
areas
• They are eat at NIGHT and feed largely on insects
and spiders
• The short cephalothorax has the appendages and
1 to 6 pair of eyes
• The postabdomen has the long slender tail of five
segments that end in a Stinger
• Scorpions bear live young carried on the mothers
back
Scorpions
Order Opiliones: Harvestmen
• Harvestmen or DADDY LONG LEGS are
common, especially in tropical areas
• Unlike spiders, their abdomen and
cephalothorax join broadly without a narrow
pedicel
• They can lose one or more LEGS of their eight
without ill effect
• Their chelicerae are pincer-like and they feed
more as scavengers than do spiders
Harvestmen
Order Acari: Ticks and Mites
• They are medically and economically the
most important arachnids
• Their mouthparts are on the tip of the
anterior capitulum
• They are both aquatic and terrestrial; some
parasitize vertebrates and invertebrates
• About 40,000 species have been described;
many more are estimated to exist
Diversity of mites and ticks
• House mites are free-living and cause ALLERGIES
• Spider mites are one of the many important
agricultural pest mites that suck out plant nutrients
• Chiggers are larval Trombicula mites; they feed on
dermal tissues and cause ITCHY RASHES
• The hair follicle mite Demodex is harmless but related
species cause mange in domestic animals
• Ticks are usually larger than mites
• Tick species of Ixodes carry LYME Disease (#1 Disease!)
• Tick species of Dermacentor transmit Rocky Mountain
Spotted Fever
• The cattle tick transmits Texas cattle fever
Subphylum Myriapoda
• Includes the centipedes, millipedes,
pauropods and symphylans
• Several classes have _____tagmata – a head
and trunk with paired appendages on the
trunk
• Myriapods only have one pair of antennae,
mandibles, and maxillae
• Legs are always uniramous (NOT __________)
• Respiration occurs through the body surface,
trachea, or gills in juveniles
Class Chilopoda: Centipedes
• Centipedes are terrestrial carnivorous PREDATORS found
under logs, bark and stones eating earthworms, cockroaches
and other insects
• Their flattened bodies have up to 177 segments
Class Chilopoda: Centipedes
• Each segment, except the one behind the head and the
last two, bears 1 pair of appendages
• Appendages of the first body segment form venom claws
• The head has a pair of eyes on either side of the head that
consist of groups of ocelli
• A pair of spiracles in each segment allows air to diffuse
through branched air tubes of the trachae
• The sexes ar separate; all are oviparous and the young
resemble the adults
• One genus of house centipede has 15 pairs of legs and
another has 21 pairs
• Most are harmless to humans but a few large,
tropical centipedes are dangerous
Class Diplopoda
• Millipedes have many legs, but not a thousand as they
are sometimes called
• Their cylindrical bodies have from 25 to 100 segments
• Two pairs of legs are present per segment, probably
from the fusion of two segments
• Each abdominal segment has two pair of spiracles
opening into air chambers and tracheal air tubes
• Most eat decayed plants but a few eat living plant
tissue so they are HERBIVORES
• After copulation, the female lays eggs in a nest and
guards them
• Larvae have only one pair of legs to each segment
Millipedes
Subpylum Crustacea
• Crustaceans include lobsters, crayfish, shrimp,
crabs, and copepods
• Most are aquatic, and free living, many are
sessile, commensal, or parasitic
• The main distinguishing characteristic of
crustaceans is that they have _____ pairs of
antennae
• The head also has a pair of mandibles and two
pair of maxillae
Typical Body Plan
Life Cycle of Gulf Shrimp
Types of Crustaceans
• Ostracods are enclosed in a bivalve carapace and
resemble tiny clams and are less than 1/16 inch long
• Most live in marine or freshwater sediments but
some scavenge or feed on detritus
Copepods
• Copepods have numerous species
• They lack a carapace and retain the simple,
median eye in the adult
• They have four pairs of flattened, biramous,
thoracic swimming appendages
• Free-living copepods may be the dominant
primary consumer in aquatic communities
• Parasitic forms are highly modified and
reduced, often unrecognizable as arthropods
Cirripedia – the barnacles
• Barnacles as adults are sessile and attach
directly or by a stalk to the substrate
• The carapace surrounds the body and secretes
a set of calcareous plates
• The head is reduced, the abdomen is absent
and the thoracic legs are long with hair-like
setae
• The many-jointed cirri that bear the setae are
extended from the plates to feed on small
particles
Isopods
• Isopods are dorsoventrally flattened, lack a carapace and have
sessile compound eyes
• The abdominal appendages bear gills
• Common land forms include the sow bugs and pill bugs
• Some isopods are highly modified as parasites of fish or
crustaceans
Amphipods
• Amphipods resemble isopods except they are
somewhat compressed laterally
• They lack a carapace and have sessile compound
eyes
• Many are marine, others are beach-dwelling,
freshwater or parasitic
Krill
• Euphausiacids or “Krill” has only 90 species but
includes the important ocean plankton called krill
• They form a major component of the diet of baleen
whales and of many fishes.
• Some are over 2 inches long
Decapods
• Decapods have five pairs of walking legs, the
first forming pincers or chelae
• They range from a few millimeters to the larges
arthropod, a Japanese crab with a 12 foot legspan
• They are true crabs with a broader cephalothorax
and reduce abdomen, compared to crayfish or
lobsters
• Fiddler crabs have a reduced abdomen and
burrow in the sand
• Hermit crabs are adapted to live in snail shells
Variety of Decapods