This document summarizes key characteristics of invertebrate animals. It describes their structures and functions including systems for digestion, respiration, circulation, excretion, response, movement, and reproduction. Specific phyla are examined in more detail, including worms, mollusks, arthropods, and echinoderms. Evolutionary trends are discussed such as the development of specialized cells/tissues, body symmetry, cephalization, segmentation, and a coelom.

1. Zoology
• Structure
• Function
• System or Systems

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

3. 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

4. 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

5. 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,

6. 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

7. 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

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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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)

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

16. 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)

17. 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

18. 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

19. 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

20. 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

21. Structure 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

22. 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)

23. 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)