Invertebrates
I. What is an Animal?
A.
B.
C.
Animal: multicellular, eukaryotic
heterotroph whose cells lack cell
walls
Invertebrate: no backbone or vertebral
column
Vertebrate: have a backbone
II. Phylum Porifera
A.
B.
C.
D.
Example: sponges
Word means “pore
bearing”
Asymmetry
Natural sponges:
nonliving material
that remains after
decay
E.
F.
G.
H.
I.
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
III. Phylum Cnidaria
A.
Examples: coral, jellyfish, sea anemone
B.
C.
D.
Cnidocytes: cells that contain stinging
poisonous barbs with which they
paralyze prey
Radial symmetry
Two body forms
1. polyp: sessile, tentacles up –
coral, hydra
2. medusa: free swimming,
tentacles down – jellyfish
E.
F.
G.
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
IV. Phylum Platyhelminthes
A.
Examples: flatworms, tapeworms,
flukes
B.
C.
D.
E.
Many parasitic forms - cause many
diseases of people and livestock
Bilateral symmetry and cephalization
(concentration of sensory organs and
nervous tissue in the head)
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
V. Phylum Nematoda
A.
Examples: roundworms (pinworms,
hookworms)
B.
C.
D.
E.
Many are microscopic
Two digestive openings: mouth and
anus – food moves only one way
Only sexual reproduction; usually
separate sexes; no regeneration
Most are free-living, many are
parasitic – you can be infected by
consuming contaminated food/water
or by being bitten by insects
VI. Phylum Rotifera
A.
B.
C.
D.
Example: rotifers
Less than 1mm long
Free swimming,
most in fresh water
Important food source
in aquatic food chains
E.
Some can reproduce by
parthenogenesis – females produce
diploid eggs that develop into female
organisms without being fertilized by
sperm (males do not exist in these
species)
VII. Phylum Annelida
A.
Examples: segmented worms,
earthworms, leeches
B.
C.
Body divided into many segments
Complete digestive tract
1. pharynx
2. esophagus
3. crop
4. gizzard
5. intestine
6. anus
D.
E.
F.
G.
May have leg-like parapoda
Closed circulatory system: blood
stays within vessels
1. main vein is dorsal (upper/back
side)
2. 5 aortic arches: function as simple
hearts
Earthworm is hermaphroditic; others
have separate sexes
Earthworms are important in the soil
ecosystem– provide passageways for
plant roots and water
VIII. Phylum Mollusca
A.
Examples: snails, clams, octopus,
squid
B.
C.
Mollusks and annelids have a true
coelom (body cavity)
Characteristics:
1. muscular foot: used for motion or
attachment – the foot may be
modified into tentacles
2. mantle: soft, outer layer of body
3. visceral mass: contains most of the
internal organs
4. gills or lungs: located in the mantle
cavity
D.
Main groups of mollusks
1. gastropods (“stomach-footed”)
a. univalves: one shell, breathe
with lungs; example: snail
b. bivalves: two shells, breathe
with gills; example: clam
2. cephalopods (“head-footed”)
- foot is modified into tentacles,
breathe with gills;
examples: octopus, squid
E.
F.
G.
Sexual reproduction: most have
separate sexes, some are
hermaphrodites
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).
Most mollusks are marine, but some
live in fresh water or on land
IX. Phylum Arthropoda
A.
B.
Largest phylum – found in almost all
places on earth
Characteristics:
1. exoskeleton
a. Outside the body
b. Very good protection
c. Does not grow, so it must be
shed periodically (molting)
C.
2. paired, jointed appendages (body
extensions)
3. segmentation
4. open circulatory system
5. ventral (lower/belly side) nerve cord
Classified based on
number and
structure of body
segments and
appendages
D.
Centipedes and Millipedes
1. most primitive arthropods
2. obvious segmentation
3. Centipedes (Class Chilopoda)
a. one pair of legs per
segment
b. poisonous fangs
for killing prey
c. long antennae
4. Millipedes (Class Diplopoda)
a. two pairs of legs per segment
b. one pair of short antennae
c. usually harmless vegetarians
E.
Crustaceans (Class Crustacea)
1. examples: lobster, crayfish, shrimp
2. most are marine
3. two body regions:
a. cephalothorax
b. abdomen (divided into 7
segments)
4. two pair of antennae (1 long, 1
short pair)
5. swimmerets: appendages on the
abdomen used for swimming
6. breathe by gills attached to the
swimmerets
7. one pair of large claws
8. 4 pairs of walking legs
F.
Arachnids (Class Arachnida)
1. examples: spiders, ticks, mites,
scorpions
2. two body regions:
a. cephalothorax
b. abdomen: no appendages on
abdomen
3. no antennae
4. simple eyes
5. 4 pairs of walking legs
6. mouthparts modified as fangs
(chelicerae) to stab prey and suck
out body fluids
7. book lungs (gills modified for
breathing on land)
G.
Insects (Class Insecta)
1. over 75% of all animal species
2. first animals to develop flight
3. Characteristics:
a. three body regions
1. head
2. thorax (with 3 pairs of legs)
3. abdomen
b. usually 1 or 2 pairs of wings
c. 1 pair of antennae
d. compound eyes
e. respiration through a system of
tubes called tracheae
4. metamorphosis: a series of changes
during which young insects develop
into adults
a. some insects
do not carry on
metamorphosis
(silverfish)
b. incomplete (gradual)
metamorphosis
(grasshopper)
1. egg
2. nymph (look like
adults, but smaller,
with no wings or
reproductive
organs)
3. adult
c. complete metamorphosis
(butterflies, bees)
1. egg
2. larva (caterpillar)
3. pupa
4. adult
X. Phylum Echinodermata
A.
B.
C.
Name means “spiny skin”
Marine environment
Radial symmetry – body parts usually
in multiples of 5
1. larvae have bilateral symmetry
2. deuterostomes - indicates a fairly
close relationship to vertebrates
D.
E.
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
F.
Examples: sea urchins, sand dollars,
starfish
XI. Comparing Invertebrates
A.
Specialized cells, tissues, and organs
1. Sponges and Cnidarians: little
internal specialization
2. Flatworms: simple organs
3. More complex invertebrates: organ
systems
B.
Body symmetry
1. sponges: no symmetry
2. cnidarians and echinoderms: radial
symmetry
3. all other phyla: bilateral symmetry
C.
Cephalization: concentration of sense
organs and nerve cells in the front of
the organism
1. sponges: no nerve tissue
2. cnidarians: nerve net
3. worms and arthropods: groups of
nerves called ganglia
4. mollusks: brain
D.
Coelom formation: body cavity
formation
1. sponges and cnidarians: two cell
layers with a jellylike material
between them
2. other invertebrates have 3 cell
layers
3. types of coeloms:
a. flatworms: no body cavity
(acoelomates)
b. roundworms: body cavity partially
lined with mesoderm
(pseudocoelomates)
c. other invertebrates: body cavity
completely lined with mesoderm
(coelomates)
E.
Embryonic development
1. blastopore: opening in the blastula
2. blastula: hollow ball of cells formed
from the zygote
3. protostomes: blastopore develops
into the mouth; examples: worms,
arthropods, mollusks
4. deuterostomes: blastopore develops
into the anus; examples:
echinoderms and vertebrates
F.
Feeding and digestion
1. intracellular digestion: food is
broken down inside cells (lower
animals)
2. extracellular digestion: food is
digested and then enters the cells –
enables digestion of larger pieces
of food (higher invertebrates)
G.
Respiration
1. diffusion through skin: many
worms
2. gills: aquatic invertebrates (many
mollusks and arthropods)
3. mantle cavity: snails
4. book lungs: spiders
5. tracheal tubes: many insects
H.
Circulation
1. open circulatory system: blood
does not stay within vessels,
empties into sinuses;
examples: arthropods, most
mollusks
2. closed circulatory system: blood
remains within vessels; examples:
annelids, some mollusks
I.
Movement and support
1. hydrostatic skeleton: fluid-filled
body cavity supports the muscles;
examples: annelids, jellyfish
2. exoskeleton: skeleton is outside
the body; examples: arthropods
3. endoskeleton: located inside the
body; examples: vertebrates
J.
Reproduction
1. all animals reproduce sexually,
some may also reproduce asexually
2. external fertilization: (usually in
water) eggs and sperm are released
into the surrounding environment
3. internal fertilization: (usually on
land) eggs are fertilized inside the
body of the female