Invertebrates
INVERTEBRATES are…
Animals that do not
have a backbone at
anytime during their
development
There are 9 major
phyla of
invertebrates
Porifera
Sponges – “Pore Bearer”
Two cell layers
* One body opening
* Asymmetrical
* Sessile
* Filter Feeders
*
Cnidaria
*
*
*
*
Two cell layers
One body opening
Radial symmetry
Stinging cells
(nematocysts)
* Two life stages:
polyp (baby)
medusa (adult)
Platyhelminthes
(flatworms)
* Bilateral symmetry
* Flattened bodies
* One body opening
* Slightly developed
nervous &
sensory systems
Tapeworms in Body
Nematoda
(roundworms)
* Tubelike digestive
system with 2
body openings
* Many parasitic
* Sensory eyespots
Heartworm—A parasitic nematode
Mollusca
* Bilateral symmetry
* Body cavity for
organs
* Complete digestive
tract with 2 openings
* Muscular foot
* Mantle (surrounds
internal organs;
secretes shell in most
mollusks)
EXAMPLES OF MOLLUSKS
* Gastropods
(1 Shell)
Snails
* Bivalves (2 Shells)
Clams
* Cephalopods
(head-footed)
Octopi, Squid
Annelida
(segmented worms)
* Bilateral Symmetry
* Coelom and two
body openings
* Segmentation—
provides for great
flexibility
* Leeches,
earthworms,
bristleworms
Arthropoda
*
*
*
*
Bilateral Symmetry
Exoskeletons
Jointed appendages
Some have fused
segments
Examples:
* Insects, spiders,
crabs, centipedes
Echinodermata
* Radial Symmetry
* Endoskeleton
* “spiny skin”
• Water vascular system
for movement—makes
suction on “feet”
* Sea Stars (starfish) Sand Dollars,
Sea Urchins, Sea Cucumbers
Sand Dollar
Sea Urchin
Sea Cucumber
Invertebrate Chordates
(most advanced of invertebrates)
* Have a notochord,
dorsal nerve cord,
gill slits, muscle
blocks
* Bilateral Symmetry
Examples: Tunicates (Sea squirts),