An invertebrate is an animal without a
backbone.
 The group includes 95% of all animal
species


There is no escaping the invertebrates!

Sharing space on your face

Animals are distinguished by their body
cavity or lack of.

Acoelomates
› lack a body cavity (coelom)
› bilateral symmetry
› one internal space, the digestive cavity
 Coelomates

have a body cavity(s)

Digestive system and body wall can move independently

Internal organs can be more complex

Coelomic fluid can assist with respiration, circulation,
excretion

The good the bad and the ugly!!!
Phylum Porifera
 Phylum Cnidaria
 Phylum Platyhelminthes
 Phylum Mollusca
 Phylum Annelida

 Phylum

Porifera
Sponges
 Sessile aquatic animals
 Some are freshwater species, most are marine
 shapes of their bodies are adapted to maximize the efficiency of
the water flow
 Phylum
›
Cnidaria
(pronounced nidaria/ with a silent c)
› phylum containing over 9,000 species of animals found
exclusively in aquatic and mostly marine environments
 Jellyfish
 Hydra
 Phylum Cnidaria
 Two basic body forms are seen :
swimming medusa and sessile polyps
 Phylum
Cnidaria
› Their distinguishing feature is a cnidocyte,
specialized cells that they use mainly for
capturing prey.
 Phylum
Cnidaria
 Have no brains or central nervous systems
 Instead they have nerve nets that generate
signals in response to various types of stimulus,
such as odors
 Phylum

Platyhelminthes
Flatworms
› Planarian
› Fluke
› Tapeworm
 no specialized circulatory or respiratory organs
oxygen and nutrients to pass through
their bodies by diffusion
 Over half of all known flatworm species are
parasitic, and some do enormous harm to humans
and their livestock
 Phylum
Platyhelminthes
Taenia solium
 Phylum
Mollusca
› Considered coelomates
 Coelom is limited to space around
the heart
 Phylum
Mollusca
 Phylum
Mollusca
 Phylum
Mollusca
 Phylum
Mollusca
› Respiratory system –gills
› Digestive system – starts with Radula
 Phylum
Mollusca
 Phylum
Mollusca
Cool Squid Stuff to look for
During dissections

Phylum Annelida
Segmented
Most have a pair of coeloms in each segment
which allows independent movement
Coelomatic fluid
*Moist environments
› Phylum Annelida
› Respiratory system
 (usually)
no specialized organs for gas exchange
 Thin, permeable body wall – surface for gas exchange
› Digestive system
 complete digestive system, with mouth and anus
 digestive tubes of earthworms have special structures, like a muscular
wall and a gizzard-peristalsis
› Phylum Annelida
› Nervous system
 two ventral nerve chords
 one relatively big nervous cell concentration
› Circulatory system
›
›
›
Closed
Move by peristalsis -waves of contractions and expansions
2 main vessels
 Dorsal moves blood anterior
 Ventral moves blood posterior
10X
magnification
› Phylum Annelida
› Reproductive system – Varies
 Asexual-budding
 Sexual
 Earthworms
 hermaphrodite



Phylum Annelida
support terrestrial food
chains both as prey
aerating and enriching soil


Minnesota?
Leeches ?

Dissecting the earthworm

FOLLOW DIRECTIONS in
your lab book

Allow 20 minutes