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Invertebrates!!
Review: What is an Animal?
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A multicellular eukaryotic heterotroph whose cells
lack cell walls
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Invertebrates have no backbone or vertebral column.
95% of animals are invertebrates.
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Vertebrates have a backbone. Only 5% of animals are
vertebrates.
What are the Invertebrates?
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Multicellular animals
Heterotrophs – take in food, digest it, distribute it
to cells
No backbone
Have locomotion, special parts for locomotion
Some are sessile
Some invertebrates can regenerate lost parts or
even a complete individual from a broken piece.
Phylum Porifera
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Sea Sponges
Means “pore bearing”
Asymmetric
Natural sea sponges:
dead material that
remains after decay
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Sessile: live attached to a surface
Do not have nerve cells or tissue
Filter feeders: pump water in and out and
feed on the organic material in water
Many are hermaphrodites: able to produce
male and female gametes – an advantage for
sessile organisms
Can reassemble when fragmented
Phylum Cnidaria
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Coral, jellyfish, sea anemones
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Cnidocytes: cells that contain stinging poisonous
barbs with which they paralyze prey
Radial symmetry
Two body forms:
polyp: sessile, tentacles up (coral, hydra, anemone)
medusa: free swimming, tentacles down (jellyfish)
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Digestive body cavity
surrounded by two
layers of cells
Sexual or asexual
reproduction – hydra
reproduces by budding
Coral reefs build up and
are important ocean
habitats
Phylum Platyhelminthes
Examples: flatworms, tapeworms, flukes
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Many parasitic forms - cause many diseases
of people and livestock
Bilateral symmetry and cephalization
One digestive opening (pharynx) to take in
food and release waste – most don’t need
complex digestive systems because food has
already been digested by their host
Most are hermaphroditic, some can
regenerate lost body parts
Phylum Nematoda
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Examples: roundworms (pinworms,
hookworms, heartworms)
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Many are microscopic
Two digestive openings: mouth and anus –
food moves only one way
Sexual reproduction
Most are free-living, many are parasitic –
you can be infected by consuming
contaminated food/water or by being bitten
by insects
Phylum Annelida
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Examples: segmented worms,
earthworms, leeches
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Closed circulatory system: blood stays within
vessels
Earthworm is hermaphroditic; others have
separate sexes
Earthworms are important in the soil
ecosystem– provide passageways for plant
roots and water.
Aristotle called earthworms “the intestines of
the soil”. What did he mean by this?
Phylum Mollusca
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Mollusks have an internal or external shell.
Examples: snails, slugs, clams, octopus,
squid, cuttlefish
Main groups of mollusks:
1. Gastropods are “stomach-footed”
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univalves: one shell (snail)
bivalves: two shells (clam)
2. Cephalopods are “head-footed”
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Foot is modified into tentacles.
They breathe with gills.
(octopus, squid)
Have you hugged
your octopus
today?
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Sexual reproduction: most have separate
sexes, some are hermaphrodites
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Most have an open circulatory system (blood
is contained within vessels that empty into
sinus cavities). Cephalopods have a closed
system (blood remains within vessels).
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Most mollusks are marine, but some live in
fresh water or on land
Phylum Arthropoda
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Arthropod means “jointed foot”
Largest phylum – found almost everywhere!
Characteristics:
1. exoskeleton
a. Outside the body
b. Very good protection
c. Does not grow, so it must be
shed periodically (molting)
2. paired, jointed appendages
(legs, antennae)
3. segmentation
Centipedes and Millipedes
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most primitive arthropods
 obvious segmentation
Centipedes (Class Chilopoda)
a. one pair of legs per
segment
b. venomous fangs
for killing prey
c. long antennae
Millipedes (Class Diplopoda)
a. two pairs of legs per segment
b. one pair of short antennae
c. usually harmless vegetarians
Crustaceans (Class Crustacea)
Examples: lobster, crayfish, shrimp, crab
Arachnids (Class Arachnida)
Examples: spiders, ticks, mites, scorpions
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two body regions:
a. cephalothorax (where legs come from)
b. abdomen
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no antennae
simple eyes
4 pairs of walking legs
mouthparts modified as fangs (chelicerae) to stab
prey and suck out body fluids
book lungs (gills modified for breathing on land)
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Insects (Class Insecta)
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Over 75% of all animal species
First animals to evolve the ability to fly
6 legs and 3 body parts
Insects undergo metamorphosis:
a series of changes during which young insects
develop into adults.
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Incomplete Metamorphosis (grasshopper)
 Gradual
1. egg
changes from nymph to adult
2. nymph
3. adult
Complete Metamorphosis (butterflies, bees)
1. egg 2. larva (caterpillar) 3. pupa 4. adult
Phylum Echinodermata
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Name means “spiny skin”
Marine environment
Radial symmetry
Deuterostomes - indicates a fairly close
relationship to vertebrates
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Water vascular system
1. system of internal tubes
2. carries out functions of circulation,
respiration, and movement
Tube feet
1. act like living suction cups
2. help in movement and feeding
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Examples: sea urchins, sand dollars,
starfish (sea stars)
Which invertebrate phyla are
represented here?