Arthropods
and
Echinoderms
Phylum Arthropoda




Most diverse phylum
Most successful of all time
About 1 million species have been identified
= more than 3 times the number of all other
animal species combined!!
What is an Arthropod


Includes insects, crabs, centipedes, and
spiders
All have segmented bodies, tough
exoskeletons, and jointed appendages
Exoskeletons




Provide protection and support
Made of protein and carbohydrate called
chitin
Vary in shape, size and toughness
Terrestrial arthropods have waxy covering
to prevent water loss
Appendages




Appendages: structures such as legs and
antennae that extend from the body wall
All are jointed
Include antennae, claws, walking legs,
wings, flippers, mouthparts, tails, and other
specialized structures
Named for this: arthron means “joint” in
Greek, and podos means “foot”
Evolution of Arthropods



First arthropods appeared in the sea more
than 600 million yrs. Ago
Live in every habitat on Earth: sea,
freshwater, land, and air
Evolution has led to fewer body segments
and highly specialized appendages for
feeding, movement, and other functions
Form and Function




Use complex organ systems
Feeding: herbivores, carnivores, and
omnivores
Bloodsuckers, filter feeders, detritivores,
and parasites
Mouthparts modified for chewing, sponging,
sucking, and probing
Form and Function





Respiration
Terrestrial arthropods breathe through
network of branching tracheal tubes that
extend throughout the body
Air enters and leaves the tubes through
spiracles: small openings located on outside of
body
Spiders have book lungs: organs with layers of
respiratory tissues stacked like a book
Aquatic arthropods use featherlike gills or
book gills
Form and Function





Open circulatory system
Well-developed heart pumps blood through
arteries that branch and enter the tissues
Leaves vessels moves through sinuses or
cavities
Collects in large sinus surrounding heart
Re-enters heart and is again pumped
through body
Form and Function



Excretion
Terrestrial arthropods use malpighian
tubules: saclike organs that extract wastes
from the blood and then add them to feces
that move through the gut
Aquatic arthropods use diffusion to move
cellular wastes from the body to the water
Form and Function





Well developed nervous systems
Have brains that receive information and send
it out to muscles
Two nerves connect brain to a ventral nerve
cord
Along nerve cord are several ganglia that
coordinate movements of individual legs and
wings
Sophisticated sense organs: compound eyes
may have more than 2000 separate lenses to
detect color and motion very well
Form and Function


Movement by well-developed groups of
muscles made of individual muscle cells that
contract and pull on exoskeleton
At each joint, different muscles either flex or
extend
Form and Function




Reproduction
Terrestrial arthropods have internal
fertilization
Some put sperm inside female, others
deposit sperm packet that female picks up
Aquatic arthropods may have internal or
external fertilization
Growth and Development






Exoskeleton does not grow, must be shed as
arthropod gets bigger
Molting: shedding of entire exoskeleton and
making a new one
Controlled by hormones
Can take several hours
Makes them vulnerable to predators while
shell is still soft
Most hide during molting or molt at night
Groups of Arthropods

Arthropods are classified based on the
number and structure of their body
segments and appendages – particularly
their mouthparts
Subphylum Crustacea




Mostly aquatic
Includes crabs, shrimps, lobsters, crayfishes,
and barnacles
Range in size from small terrestrial pill bugs
to enormous spider crabs up to 20
kilograms
Typically have 2 pairs of antennae, 2 or 3
body sections, and chewing mouthparts
called mandibles
Subphylum Crustacea




Cephalothorax: anterior, fusion of head with
the thorax
Thorax: holds internal organs
Abdomen: posterior part of the body
Carapace: part of the exoskeleton covering
the cephalothorax
Subphylum Crustacea




1st 2 pairs of appendages are antennae
covered in sensory hairs
Used as sensory organs, filter-feeding, or
swimming
3rd pair are the mandibles adapted for biting
and grinding food
Gills are attached to appendages associated
with the cephalothorax
Subphylum Crustacea







Decapods: crayfish, lobsters, and crabs
Largest group of crustaceans
Five pairs of legs
1st pair of legs called chelipeds, bear large claws
modified to catch, pick up, crush and cut food
4 pairs of walking legs
Along abdomen are several pairs of swimmerets:
flipperlike appendages used for swimming
Final abdominal segment is fused to form a large,
flat tail: uropod
Subphylum Chelicerata





Includes horseshoe crabs, spiders, ticks, and
scorpions
Have mouthparts called chelicerae and two
body segments and 4 pairs of walking legs
No antennae
Cephalothorax contains brain, eyes, mouth,
and walking legs
Abdomen contains internal organs
Subphylum Chelicerata




Chelicerae contain fangs used to stab and
paralyze prey
Pedipalps used to grab prey
Respire with either book gills or book lungs
Two main classes: Merostomata and
Arachnida
Subphylum Chelicerata








Class Merostomata
Includes horseshoe crabs
Oldest living arthropods: first appeared 500
mya
Not true crabs at all
Anatomy similar to spiders
Have chelicerae, five pairs of walking legs, and
long spikelike tail
Can grow to size to frying pan
Common along eastern US coast
Subphylum Chelicerata




Spiders: largest group of arachnids
Capture food in a variety of ways: webs
made of protein called silk, stalk and pounce
on prey (turantula), lie in wait then grab
Feed on animals ranging from other
arthropods to small birds
No jaws for chewing, must liquefy food to
swallow it
Subphylum Chelicerata




Once prey is caught, fangs inject paralyzing
venom
Once prey is dead, spider injects digestive
enzymes into the wounds
Spider sucks out tissues into a specialized
pumping stomach
Food then moves to the rest of the digestive
tract being further broken down by
enzymes
Subphylum Chelicerata






All spiders produce silk even if they don’t spin
webs
Stronger than steel!
Used for webs, cocoons for eggs, wrappings for
prey
Force liquid silk through spinnerets: organs
that contain silk glands
As silk comes out it hardens into single strand
Spinning webs seems to be preprogrammed
behavior
Subphylum Chelicerata





Mites and Ticks: small and often parasitic
Specialized chelicerae for piercing tissue
and sucking out blood
Pedipalps are often equipped with claws for
holding on to host
Parasitize plants and animals
Can cause itching, painful rashes, and
transmit diseases such as Rocky Mtn.
spotted fever and Lyme disease
Subphylum Chelicerata




Scorpions: widespread in warm areas
including southern US
Pedipalps enlarged into claws
Long, segmented abdomen has a venomous
stinger that can kill or paralyze prey
Chew up prey with chelicerae
Subphylum Uniramia






Includes centipedes, millipedes, and insects
Response to stimuli
Compound eyes
Chemical receptors for taste and smell on
mouthparts, antennae and legs
Sensory hairs to detect movement
Well-developed ears that hear above human
range; found in strange places (behind legs
in grasshoppers)
Subphylum Uniramia





Adaptations for feeding
3 pairs of appendages for mouthparts
including mandibles
Saliva contains digestive enzymes
Bee saliva help change nectar into honey
Glands in bee’s abdomen secrete wax, used
to build beehives
Subphylum Uniramia




Movement and Flight
Legs used for jumping, walking, capturing
and holding prey
Flying insects usually have two pairs of
wings made of chitin
Flight has allowed for movement worldwide
and wide variety of habitats
Subphylum Uniramia





Metamorphosis: process of changing shape
and form
2 types: incomplete and complete
Incomplete metamorphosis: gradual change
with nymph immature forms
Nymphs lack sexual organs and wings and
usually look similar to the adult form
Complete metamorphosis: dramatic change
with larval stage and pupa
Insect Communication





Use sound, visual, chemical, and other types
of signals
Most communication is for mating
Sound: crickets chirping by rubbing legs
together; cicadas buzz by vibrating special
membranes on their abdomens
Visual cues: fireflies lighting up
Chemical signals: pheromones used for
alarm or alerting other insects and for
mating
Insect Societies




Ants, bees, termites, and some of their
relatives form complex associations called
societies
Societies work together for the benefit of
the whole group
Can have more than 7 million individuals
Castes: groups of individuals performing a
certain job or role in the society (queen,
workers, drones, etc)
Classification for Subphylum Uniramia



Centipedes: Class Chilopoda
Millipedes: Class Diplopoda
Insects: Class Insecta










Order Orthoptera: Crickets, grasshoppers, locusts
Order Isoptera: termites
Order Hymenoptera: bees, wasps, and ants
Order Lepidoptera: butterflies and moths
Order Diptera: true flies
Order Coleoptera: beetles
Order Hemiptera: true bugs
Order Anoplura: human louse (lice)
Order Odonata: dragonflies
Order Dictyoptera: cockroaches and mantids