Mollusks

2.  50,000 or more species of molluscs.
 Characteristics:
 Bilateral symmetry.
 Body enclosed by a blanket-like mantle that secretes
a shell made of calcium or some other stiff structure.
 A mantle cavity between the mantle and the internal organs;
the anus, reproductive, and excretory ducts open into the
mantle cavity.
 A ventral, muscular foot that is highly modified among
the various groups of molluscs.
 Head withy sensory organs and a mouth.

3.  Characteristics:
 Aquatic mollusks have gills. Terrestrial mollusks have
lungs.
 Herbivorous or carnivorous. All of them with a complex
digestive system.
 Most of them are hermaphrodites.
 In separate sexes individuals, there is no sexual
dimorphism.
 Most of them lay eggs from which a larvae emerges. It
will go under metamorphosis.
 Have a true heart
 Simple to complex nervous system

5.  Some mollusc habitats include:
 Marine (mostly)
 Freshwater (a few)
 Land (a few)
 Mollusc niches (life-style):
 Most live on the ocean bottom and are mostly
sedentary
 Some are free-swimming (the cephalopods)

6.  There are seven mollusc classes. We will
study 3 of them:
 Gastropoda (gastro=body cavity;
poda=foot)
 Ex. Common garden snail, limpets and slugs

7.  There are seven mollusc classes. We will
study 3 of them:
 Gastropoda (gastro=body cavity;
poda=foot)
 Ex. Common garden snail, abalone, turban
snail
 Bivalvia (bi=two; valvia=valves)
 Ex. Clam

8.  There are seven mollusc classes. We will
study 3 of them:
 Gastropoda (gastro=body cavity;
poda=foot)
 Ex. Common garden snail, abalone, turban
snail
 Bivalvia (bi=two; valvia=valves)
 Ex. Clam
 Cephalopoda (cephalo=dealing with
head; poda=foot)
 Ex. Squid, octopus, sepia, nautilus, etc.

9. LIMPET SLUG SNAIL

10.  Most popular class of molluscs.
 Consists of snails and snail-like creatures.
 Specific characteristics:
 They have a dorsally located shell (often coiled).
 They have a well-developed radula.
 4 tentacles (2 optic and 2 sensory)

11.  Most popular class of molluscs.
 Consists of snails and snail-like creatures.
 Specific characteristics:
 They have a dorsally located shell (often coiled).
 They have a well-developed radula.
 4 tentacles (2 optic and 2 sensory)
 Visceral mass (organs) almost always located
inside the shell. Their visceral mass is rotated 180
degrees during development.
 They are herbivores or predatory (carnivorous).
 Habitats include: ocean, lake, river bottoms,
coastal shores, and land. Terrestrial have lungs
and aquatic have gills.

12. MUSSEL CLAM
COCKLE
SWORD RAZOR

13.  They have no head.
 They have two shells held
together by powerful muscles.
 They have a ventrally located foot
that sticks out between the two
valves.
 They tend to burrow into soft mud
or sand or attach to rocks or
other shells.
 Habitats include: marine and
freshwater.
 Large gills are used for respiration
and filter feeding.
 Water enters and exits through
siphons.

15. OCTOPUS
NAUTILUS SEPIA
SQUID

16.  Contains the largest molluscs.
 Specific Characteristics:
 May lack a shell (like an octopus)
 Shell may be reduced to a stiffening rod (like the squid or
nautilus)
 The foot is highly modified to form a group of tentacles
around the mouth.
 They are found in deep and shallow waters along many
coasts.
 Squids & Nautilus are free-swimming and move very
quickly. Octopuses are found among rocks or crawling on
the bottom of the ocean.
 Complex brain, two lateral eyes, excellent eyesight.