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Unit 18: Biology Part 1 Page 10 of 60
Objectives
Lesson 1: Invertebrates
This lesson covers the wonderful Roundworms only have a body
world of spineless creatures— cavity, and segmented worms have
invertebrates. Invertebrates are both a body cavity and segments.
animals without backbones Some worms are parasitic (the
tape-worm, for example) while
There are many different types of others are not (like the sea
invertebrates: from starfish to bees flatworm).
to worms to sea angels! Here are
the different types we’re going to Mollusks—including mussels,
learn about: scallops, and oysters—live in
shallow water. The mollusk body
Sponges are colonies of specialized plan generally involves a muscular
cells. They feed by filtering the foot for locomotion, a body housing
water around them. They are organs, a head with eyes or
bound to the ground beneath tentacles, and a mantle (which
them. They have no nerves. They creates the shell). Usually, they
are held together through the absorb oxygen from the water
cooperation of the colony. using gills.
There are two basic body forms of Echinoderms, meaning “spiny
Cnidarians; polyp and medusa. All skin”, are radial symmetric marine
Cnidarians have stinging cells, animals. They are found at all
called nematocysts. They all also depths—both shallow and deep
have radial symmetry. Cnidarians water. They play important roles in
are more developed than sponges; their ecosystems. Despite
they have real tissues, a body appearances, they do not have
cavity, and nerves. skeletons. The “spiny skin” is, in
fact, skin covering a spiny
Key physical differences between endoskeleton (internal skeleton).
worms can depend on whether They have water vascular systems.
they possess a body cavity and/or
segments. Flatworms have neither
a body cavity nor segments.
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