Phylum Mollusca
• The mollusks are invertebrate animals
known as Mollusca.
• There are more than 150,000 species
within this phylum.
Types of Molluscs
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•
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•
•
snails
clams
squid
cuttlefish
octopus which are among the most
neurologically-advanced
invertebrates
Commercial Use
• There are a wide variety of molluscs
valued by humans as seafood or for
their decorative shells.
• The edible species include many kinds
of clams, snails, squid and octopuses.
octopus
• Order Octopoda have venon
glands in their beaks
Mollusca
Classes of Mollusks
1) Class: Gastropoda
2) Class: Bivalvia
3) Class: Cephalopoda
4) Class: Polyplacophora
Characteristics of Mollusks
• soft-bodied animals that includes: snails, clams, and sea
slugs.
• The most common characteristic of most mollusks is
their shell. Snails are univalves, which means they have
one shell.
• The bivalves, or two-shell, mollusks include the clams,
scallops, and oysters, the oyster produces the pearl.
• Some mollusks have lost their shells altogether. The
octopus, the squid, and the sea slugs have evolved their
own survival strategies to replace their protective armor
• It is due to the absence of a protective shell the octopus
has evolved the largest and most complex brain of all the
mollusks
Characteristics continued
• All members of mollusks have a
muscular bag surrounding the gills and
organs called the mantle
• Most mollusks have a muscular foot
(squid have tentacles)
• Mollusks have radula (teeth used for
scraping/feeding)
• Mollusks develop as a trochophore and
then into a veliger
Class Gastropoda
Class Gastropoda
• gastropods are common in both salt
and fresh water and on land.
Triton shell
Nudibranch
Nudibranch
Nudibranch
snails, whelks, periwinkles, abalone, and
slugs, are the largest group of mollusks
periwinkle
abalone
Garden slug
snail
Class Bivalvia
• bivalves include clams, oysters, scallops, and mussels
• they have two parts, or valves, into which the shell is
divided. One or two large, well-developed adductor
muscles (the edible part) are used to close the shell
• Bivalves lack defined heads
• they also have no radula. A foot is present but laterally
compressed
• Bivalves generally have a large mantle cavity with gills
• the edges of the mantle may be fused to form siphons
that circulate water to and from the gill chamber.
Scallop
Left and Right Sides
Class Cephalopoda
• The cephalopods (the “head-foots”)
• the most evolutionarily advanced animals
to be found among the invertebrates.
• strictly marine class
Reef Squid
Cuttlefish
Blue-ring octopus
Chambered nautilus
Class Polyplacophora
• Chitons are primitive marine mollusks.
• Chitons have a shell that is made of eight separate shell plates. The
plates provide protection, allow the chiton to flex upward when
needed for movement, and to curl up into a ball.
• The shell plates are surrounded by a structure known as a girdle.
Chiton
Chiton
Phylum
Brachiopoda
Brachipod