Download Chapter 4 The Chemical Basis of Life

Chapter 23
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Section 4 –
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Section 6 –
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Section 9 –
Invertebrate Diversity
Diverse animals share several key
characteristics
Sponges are relatively simple animals with porous
bodies
Cnidarians are radial animals with stinging cells
Flatworms are the simplest bilateral animals
Roundworms and rotifers have complete digestive
tracts
Annelida are segmented worms
Mollusks show diverse variations on a common
body form
Echinoderms have spiny skin and a water vascular
system
Animal diversity “exploded” during the Cambrian
period
The Body of a Mollusk
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Although squids, clams, and snails look different from
each other, these animals all have certain features in
common that classify them as mollusks (phylum
Mollusca).
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Definition: member of a group of invertebrates
characterized by a muscular foot and a mantle
All mollusks have a muscular mass of tissue called a
foot and a multifunctional structure called a
mantle.
The mollusk foot functions in locomotion, but its
structure is very different from a human foot.
The mantle produces the shell in mollusks such as
clams and snails.
 Definition: body surface outgrowth that drapes over a
mollusk
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The mantle also functions in respiration, waste
disposal, and sensory reception.
The mantle is related to another distinctive
feature called the mantle cavity – this is where
the gill is located.
 The gills extracts oxygen dissolved in the water and
sometimes disposes of wastes.
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Another body feature found in many mollusks is a
unique rasping organ called a radula.
 Definition: scraping organ characteristic of
mollusks
 An aquatic snail’s radula extends from the mouth and
slides back and forth like a garden rake, scraping and
scooping algae off rocks.
 Other mollusks use their radulas to drill through shells
to prey on other mollusks.
All mollusks have a coelom – a snail’s coelom
consists of three cavities:
 one around the heart
 one around the reproductive organs
 one that forms part of the kidney
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Most mollusks have an open circulatory system that
includes a heart that pumps blood into vessels.
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Definition: blood transport system in which blood is
pumped into chambers where it comes in direct contact
with tissues and organs
The Diversity of Mollusks
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The phylum Mollusca is very diverse, with about 150,000
known species.
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Gastropods make up the largest group of mollusks.
 Definition: member of a group of mollusks that
includes snails and slugs
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CLASS: Gastropoda
Most organisms in this class have a single shell that is often
spiral-shaped.
Gastropods live in freshwater, saltwater, and terrestrial
environments.
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Bivalves include clams, oysters, mussels, and scallops.
 Definition: member of a group of mollusks with
hinged shells, such as clams, mussels, scallops,
and oysters
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Most gastropods are marine – land snails and slugs are the
only mollusks that live on land.
CLASS: Bivalvia
Bivalves have hinged shells divided into two halves.
Most bivalves live in marine or freshwater environments –
they use their muscular feet for digging and anchoring in
the mud or sand.
Bivalves feed by pumping water over their gills and
trapping food particles that are suspended in water.
Cephalopods such as squids and octopuses are faster
and more agile than gastropods and bivalves.
 Definition: member of a group of mollusks that
includes squids and octopuses
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CLASS: Cephalopoda
The cephalopods called chambered nautiluses have external
shells, but in most cephalopods the shell is small and internal
(squids) or missing altogether (octopuses).
Cephalopods are marine predators, using beak-like jaws and a
radula to crush or rip prey apart.
Their mouth is at the center of their foot, which is surrounded
by 8-10 inch long tentacle-like arms that catch and hold prey.