Download Chapter 28 Arthropods and Echinoderms

Chapter 28 Arthropods and
Echinoderms
Introduction to Arthropods
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“jointed feet”
Most diverse and successful animals
Over 750,000 species identified
Segmented bodies
Tough exoskeleton
Jointed appendages
Body Terms
• Exoskeleton- external skeleton that protects
and supports the body
– Made of protein and a carbohydrate called chitin
– Much variation on exoskeletons
– Terrestrial arthropods (Ter. Arth.) have waxy
covering to prevent water loss
• Appendages- structures like legs and
antennae that extend from the body wall
Evolution has led to:
• Fewer body segments
– The body segments fused together
• Highly specialized appendages
– For feeding, movement, and more
– Legs became: antennae, claws, wings,
flippers, tails, mouthparts and walking legs
Form and Function
• Feeding
• Varied eating habitsherbivores, carnivores,
omnivores
– Bloodsuckers, filter
feeders, detritivores,
parasites
• Varied mouthpartspincers, fangs, jaws
Respiration
• Tracheal tubes- branching, air filled tubes that
are in many ter. arth.
• Spiracles- small openings alongside the body
that allow air to enter and leave the tracheal
tubes
• Book lungs- organs with layers of respiratory
tissue stacked ex) spiders
• Gills- used by aquatic arthropods ex) crabs
• Book gills- used by horseshoe crab
Circulation
• Open circulatory system- well developed
heart pumps blood  arteries  tissues
sinus  collects around the heart and
re-enters to be pumped through again
Excretion
• Malpighian tubules- saclike organs that
extract wastes from blood and add them to
feces to move through the gut
– Used in ter. Arth.
• Diffusion- moves cellular waste from the
body to the water
– Used in aquatic arth.
Response
• All have a brain
• Well developed nervous system
• Two nerves around the esophagus
connect brain to the central nervous cord
– Connects the ganglia which coordinate
movement of legs and wings
Movement
• Well developed muscles
controlled by nervous system
• Individual muscles cells
• Muscles generate force (to
fly, walk, swim) by
contracting a muscle and
pulling on the exoskeleton
Reproduction and Molting
• Terrestrial
– Internal fertilization
• Aquatic
– Internal and external
fertilization
• Molting
– When an arthropod sheds its entire exoskeleton
and makes a larger one in its place
– Controlled by the endocrine system with
hormones
Subphyla of Arthropods
• Crustacea – crabs, shrimp, crayfish
• Chelicerata – spiders, ticks, scorpions
• Uniramia – millipedes, centipedes
• Class Insecta (no subphylum)– 3 part
body, 3 pairs of legs
28-4 Echinoderms
• “spiny skin”
• Endoskeleton- hardened plates of calcium
carbonate
– Gives bumpy, irregular surface
• Only live in the sea
• No cephalization
• Two sided- oral
(with mouth)/aboral
Echinoderm Characteristics
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Spiny skin
Internal skeleton
Water vascular system
Suction cup structure called tube feet
5 part radial symmetry
– Larvae- bilaterally symmetrical
• Deuterostomes
Water Vascular System
• Carries out essential body functions like
respiration, circulation and movement
• Madreporite- opening to the outside
through which water passes
– Connects to ring canal which extend out into
radial canals along the 5 arms
• Tube feet- suction cups on the underside
of the body that help with movement and
feeding
Feeding
• Urchins- scrape algae
• Sea lilies- capture floating
plankton
• Sea cucumbers- take in
sand and detritus off sea
floor
• Sea stars- use tube feet to
pull open bivalves, push
stomach out, pour enzymes
and digest mollusks, brings
back stomach into body
Respiration and Circulation
• Water vascular system
• Thin walled tissues of tube feet for
respiration
• Skin gills gas
exchange
Excretion
• Digestive wastes- feces through anus
• Ammonia excreted through tube feet
Response and Movement
• Don’t have highly developed nervous
system
• Nerve ring around the mouth
• Sensory organs that detect light
• Tube feet
• Endoskeleton structure/flexible joints
Reproduction
• External fertilization
• Separate sexes
Groups of Echinoderms
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Urchins
Sand dollars
Brittle stars
Sea cucumbers
Sea stars
Sea lilies
Feather stars
Ecology
• Urchins control algae
• Sea stars control clams
and corals
• Crown of Thorns
– Feeds on corals
– Rows of poisonous
spines on arms
– Great Barrier Reef
damage