Simple Invertebrates
Sponges, jellyfishes and coral,
flatworms, roundworms, and
segmented worms too!
So what do you know about simple
invertebrates?
Do you know the main characteristics of
each of the five phyla?
Let’s check them out.
Phylum Porifera
(Sponges)
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Simplest animals of all (some of the oldest too).
All are aquatic (freshwater and marine).
Only two layers of cells, but no tissues or organs!
Their skeletons are made of tiny spines called
spicules.
Cannot move (grow attached to the bottom).
Mostly filter feeders.
Uses?
The mighty sponge!
Phylum Cnidaria (aka Coelenterata):
Jellyfishes and Corals
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More advanced than sponges. (for example, they
have tissues, but still no organs).
Their body is a hollow cavity with only one opening
(for food AND wastes)!
Entirely aquatic (freshwater and marine).
All have stinging cells, but not all can harm people.
Some are pretty nasty predators. Others filter-feed
on small particles and organisms in the water.
Medusae vs. Polyps
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MEDUSAE
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POLYPS
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Ex. Jellyfishes.
A medusa is free-swimming.
Most are solitary.
Their opening is on the
bottom of their body.
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Ex. Corals
Polyps are like an upside
down medusa.
Their opening is on the top
of their body.
Coral polyps are tiny and live
in huge colonies of
thousands.
Corals build their “home” as
the colony grows larger and
larger.
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Jellyfish
Most jellyfish are harmless to people, although not so
to small fish and other marine organims.
Portuguese man-of-war.
Look out!
Corals: beautiful colonies of polyps.
More Cnidarians: hydra and sea anemones.
Is it a medusa or a polyp?
Not to confuse you, but did you know that jellyfish start
their lives as polyps, but become medusae as an adult?
It’s true! Here is a jellyfish life cycle.
Phylum Platyhelminthes
(Flatworms)
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Even more complex.
Long, flat body.
Clearly defined head with mouth.
Some have senses, a few even have eyespots.
Some move freely.
Many are parasites (ex. Tapeworm).
Some live in the water (fresh or marine), others live inside their
host!
Flatworms
Phylum Nematoda
(Roundworms)
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Another step up the ladder!
Some even have a simple nervous system.
Some have a digestive system that runs through the entire body
-- with two openings, one for food to enter and one for wastes to
leave.
Most are parasites.
Many are harmless microscopic critters that live in the soil.
Also, the trichina worm (in pork), as well as hookworms and
heartworms (common in pets).
Roundworms!
One teaspoon of garden soil may
contain as many as 10,000 tiny
nematodes (roundworms) in it!
Phylum Annelida
(Segmented Worms)
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Most complex worms of all.
Tube-like body divided into segments.
Sophisticated digestive system! (mouth, crop and gizzard,
intestine, anus)
Many other specialized organs heart, blood vessels, nerve
cords, simple brains)
Can move well.
Some aquatic (leeches, clam worms), some terrestrial
(earthworms).
Some are parasites (leeches), others are very important
decomposers (earthworms).
Any other uses for annelids?
Phylum Annelida
(Segmented Worms)
So NOW what do you know about the simple
invertebrates?
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Do you know the names of the five phyla of simple
invertebrates?
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Do you know the main characteristics of each of the
five phyla?
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Can you identify examples of animals in each of the
five phyla?