Invertebrates
• Sponges, Cnidarians, Worms, Mollusks,
Annelids, Arthropods, Echinoderms
• Each group of organisms have specific forms
and functions
• Feeding
• Respiration, circulation and excretion
• Response
• Movement
• Reproduction

Worms
• Free-living or parasites
• Segmented or unsegmented
• Flatworms – soft, flattened worms that have
tissues and internal organ systems,
• simplest animals to have three embryonic germ
layers (ectoderm, endoderm, mesoderm),
bilateral symmetry and cephalization
• Carnivores – single opening for digestive system
• Use diffusion to move materials
• Use ganglia (bundle of nerve cells) to respond to
external stimuli

Cont.
• Cilia and muscles are used for movement
• Reproduce using sexual (hermaphordites)
or asexual by the process of fission
(splitting)
• Three groups;
• Turbellarians – free-living, fresh or marine
water
• Flukes – parasitic, internal organs (blood)
• Tapeworms-parasitic, intestines

Nematoda
• Roundworms are unsegmented worms that have
two opening, anus and mouth
• Have specializes tissue and organ systems
• Consumers
• Diffusion to move materials
• Very simple nervous systems for response
• Muscles allow for movement
• Sexual reproduction – individuals (male and
female)
• Diseases – trichinosis, elephantiasis,

Annelids
• Segmented bodies, complex organ
systems that are unique due to
segmented body plan
• Filter feeders and predators
• Closed circulatory system – dorsal vessel
moves toward head and ventral moves
toward tail
• Aquatic breathe through gills, land through
skin

Cont.
• Removes waste from digestion through anus
and cellular waste by nephridia
• Have a well developed nervous system and
fundamental brain to respond to stimuli
• Have two major groups of body muscles that
function as part of the hydrostatic skeleton for
movement – longitudinal head to end (fatter or
short) circular around body contract to make
worm longer and thinner

Cont.
• Hermaphrodites: have both sperm and
eggs
• 3 Types of Annelids
• Oligochaetes
• Leeches
• Polychaetes

Mollusks
• Soft-bodied animals that usually have an
internal or external shell
• Have four parts: foot, mantle, shell,
visceral mass
• Herbivores, carnivores, filter feeders,
detritivores or parasites
• Breathe through gills or across skin
• Open or closed circulatory systems

Cont.
• Cells release Nitrogen containing waste
into the blood in the form of NH3 and
removed by nephridia
• Simple organisms (clams) have nervous
systems made of ganglia, more complex
organisms have (octopi) have very
complex nervous systems and a highly
developed brain

Cont.
• Movement depends on species – snails
secrete mucus and move with a rippling
motion along – octopus use jet propulsion
• Reproduction depends on species – some
are hermaphrodites, other release egg
and sperm by external fertilization
• 3 types of mollusks –
• Gastropod, bivalves, cephalopods

Arthropods
• Insects, crabs, centipedes and spiders
• Segmented body, tough exoskeleton and
jointed appendages
• Natural selection and other process has
led to fewer body segments, highly
specialized appendages for feeding,
movement and other functions

Cont.
• Herbivores, carnivores and omnivores
• Breathe oxygen through specialized
organs (tracheal tubes, book lungs)
• Open circulatory system
• Excretes waste through specialized
organs
• Well developed nervous system, ALL have
a brain

Cont.
• Movement provided by well developed
muscles controlled by nervous system
• Internal or external reproduction
depending on the species
• growth - outgrow exoskeleton by molting
• Classified by number and structure of
segments and appendages (specifically
mouth parts)

Cont.
• Crustaceans, spiders (and relatives),
insects (relatives)

Insects
• Body divided into 3 parts – head, thorax (3
pairs of legs attached), abdomen
• Use sense organs to respond to stimuli
compound eyes, chemical receptors,
sensory hairs, well developed ears
(beyond human range)
• Mouth part used for feeding
• Movement uses legs (walking, jumping,
holding prey)

Cont.
• Metamorphosis – complete (look nothing
like parent) or incomplete (look a lot like
parent)
• Complex social order system called
societies using a “language” to
communicate information

Echinoderms
• Spiny skin, internal skeleton, water
vascular system, suction structures,
exhibit five-part radial symmetry (star fish)
• Water vascular system carries out
essential body functions respiration,
circulation and movement
• Sea urchins, sea cucumbers, sea stars
• Crown of thorns – major threat to coral

Evolution
• 575 to 543 million years old – Ediacaran
• Soft bodied with little specialization
• By Cambrian (544 mil yrs) period many
had formed shells, skeletons and other
hard body parts

Evolutionary Trends
• Specialized cells, tissues, organs
• Body symmetry - All invertebrates except
sponges exhibit some type of body symmetry
• Cephalization – respond to environment in more
sophisticated ways
• Segmentation – increased body size
• Complex animal phyla have a true coelom that is
lined completely with tissue derived from
mesoderm

Form and Function
• Digestion: Intercellular (digested inside
cell) or extracellular (in digestive cavity
then absorbed) design
• Respiration: large moist surface area in
contact with air and water where diffusion
can take place
• Circulation: move blood through one or
more hearts and an open or closed
circulator system

Cont.
• Excretory: removal of ammonia aquatic-
diffusion / terrestrial ammonia is converted
to urea (less toxic) released through
excretory pores
• Response: 3 trends – centralization
(simplest nervous system), cephalization
(brain), specialization (sense organs)

Cont.
• Movement and support: 3 main kinds of
skeletal systems – hydrostatic (fluid filled),
exoskeleton (outside body),
endoskeletons (inside body)
• Reproduction: sexually and asexually
depending on organism – external
(outside body) internal (inside body)