Ch 28- Arthropods and Echinoderms
• biology: the science of life: world of animals | Discovery Education
• Phylum Arthropoda
– Most diverse and successful animals of all time
• Inhabit air, land, water
– Features are highly adapted
• Arthropods have
– Segmented body parts
– Tough exoskeleton (cuticle) made of chitin
– Jointed appendages
• Classified based on number and structure of their body segments and
appendages
• Major groups include
– Crustaceans
– Chelicerates
– Insects
Crustaceans
• Subphylum Crustacea
– Evolved as marine arthropods
• Crustaceans share several common features
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Two distinct body sections, cephalothorax and abdomen
One pair of appendages per segment
Two pairs of antennae
Exoskeleton
Carapace
• Appendages used for variety of functions
– Collecting and manipulating food
– Attracting females
– protection
Crustaceans
• Crustaceans vary in both anatomy and structure
• Types include
– Decapods- lobsters and crabs have ten legs; largest
group
– Barnacles- sessile filter feeders wrapped in hard shell
– Isopods- such as pill bugs have flattened bodies and
seven pairs of legs
– Tongue worms- parasites found in a host’s lungs or
nasal passages
Chelicerates
• There are three major
groups of chelicerates
– Horseshoe crabs- oldest
living arthropods
– Sea spiders
– Arachnids- spiders, mites,
ticks, and scorpions
• Chelicerates share several
features
– No antennae
– Four pairs of walking legs
– One pair each of chelicerae
and pedipalps
Arachnids
• Arachnids- group of
chelicerates that live on
land
– Eight legs
– Fanglike pincers that
inject venom
– Silk glands
Uniramians
• Subphylum Uniramia or
uniramians
– Most species of all animals
• Uniramians have
– Jaws, one pair of antennae,
unbranched appendages
• Uniramians include
– Centipedes
– Millipedes
– Insects
Insects
• What are the
distinguishing features
of insects?
– Body divided into 3
parts- head, thorax, and
abdomen
– 3 pairs of legs attached
to thorax
• Why are insects so
successful?
Insects undergo metamorphosis
• Incomplete
metamorphosis, insects
look like miniature
adults when they hatch
• There are three life
stages of incomplete
metamorphosis
– Larva
– Nymph
– Adult
• In complete
metamorphosis, the
insect changes form
entirely
• There are three life
stages of complete
metamorphosis
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Egg
Larva
Pupa
Adult
Echinoderms
• biology: the science of life: world of animals | Discovery Education
• Phylum Echinodermata
• Echinoderms have
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Spiny skin
Internal skeleton
Water vascular system- What is it’s function?
Tube feet
Most exhibit 5-part radial symmetry
• Endoskeleton- an internal skeleton formed of hardened plates of
calcium carbonate
• Live only in the sea
• Deuterostomes- animals in which the blastopore develops into an
anus
Types of Echinoderms
• There are five groups of
echinoderms
– Feather stars and sea lilies
– Sea stars
– Brittle stars and basket
stars
– Sea urchins, sea biscuits,
and sand dollars
– Sea cucumbers
• Some echinoderms can
regenerate limbs or other
body parts
Metamorphosis
• Process of changing shape and form
• Under go either incomplete or complete metamorphosis
• Incomplete metamorphosis- immature forms of insects
look very much like adults
– Nymphs- immature forms of adult insects
– Lack functional sexual organs and wings
• Complete metamorphosis- eggs hatch into larvae, look and
act nothing like their parents and feed in different ways
– Larva- look and act nothing like parents, feed in different ways
and grow rapidly, molt a few times
– Pupa- insect changes from larva to adult
– Video -- World's Weirdest: Honey Bee Dance Moves -- National
Geographic
• Cephalothorax- formed by fusion of head with thorax
• Thorax-body part lies just behind head where most
internal organs are
• Abdomen- posterior part of arthropod’s body
• Carapace- part of exoskeleton that covers
cephalothorax
• Mandible- mouthpart adapted for biting and grinding
food
• Chelipeds- first pair of legs, have large claws for
catching, picking up, crushing, and cutting food
• Swimmerets- flipperlike appendages used by decapods
for swimming
• Barnacles- sessile, no abdominal segments and don’t
use mandibles
– Attach themselves to rocks and marine animals
Spiders and Their Relatives
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Subphylum Chelicerata- Chelicerates
Horseshoe crabs, spiders, ticks, and scorpions
2 body sections- cephalothorax and abdomen
4 pairs of walking legs
Lack antennae
Book gills or book lungs
Chelicerae- mouthpart that contains fangs, used
for stabbing and paralyzing prey
• Pedipalps- long and modified for grabbing prey
• Horseshoe crabs- oldest living arthropods
– Chelicerae
– 5 pairs of walking legs
– Long spikelike tail
• Spiders- largest group of arachnids
– Spin silk webs
– No teeth, paralyze prey and use digestive enzymes to break down
prey’s tissue
– Spinnerets- organs that contain silk glands
– Video -- Black Widow: Most Venomous Spider in North America -National Geographic
• Mites and ticks- often parasitic
– Chelicerae- needlelike structures used to pierce skin and suck blood
• Scorpians- widespread in warm areas
– Pedipalps enlarged into claws
– Venomous stinger
– Chew prey using chelicerae
Insects and their Relatives
• Subphylum Uniramia or uniramians- centipedes, millipedes,
and insects
• Most species of all animals
• Jaws, one pair of antennae, unbranched appendages
• Centipedes- class Chilopoda
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Few to 100 pairs of legs
One pair per body segment
Carnivores
Moist or humid areas
• Millipedes- class Diplopoda
– 2 pairs per body segment
– Feed on dead, decaying plant material
• Water vascular system- system of internal
tubes, carries out many essential functionsrespiration, circulation, movement
• Madreporite- sievelike structure through
which water vascular system opens to outside
• Tube foot- structure that operates like suction
cup, allows echinoderms to walk and pull
open shells
Groups of Echinoderms
• 7000 species of echinoderms
• Live in oceans
• Sea urchins and sand dollars, brittle stars, sea
cucumbers, sea stars, sea lilies, and feather
stars