CHAPTER 2

Section 1

• Background information about Mollusks– They belong to the

phylum Mollusca– Live nearly

everywhere on Earth– Most live in water • Mountain streams

to the deep ocean– Some live on land in

damp locations.

ABOUT MOLLUSKS

• Background Information about Mollusks – Bilateral symmetry

– All organs are located in 1 area.

– Open circulatory system for the 1st time. • This allows an

animal to be bigger

ABOUT MOLLUSKS

• What is a mollusk?– Invertebrate with a

soft, unsegmented body that is protected by a hard outer shell.

– They have a thin layer of tissue called a mantle over their internal organs.

– The mantle also produces the mollusk’s shell. • Respiratory organ

for land mollusks

MOLLUSKS

• What is a mollusk?– They move with a

muscular structure called a foot.

– Different mollusks have feet adapted for different uses such as crawling, digging, or catching prey

MOLLUSKS

TYPES OF MOLLUSKS

Clam

Oyster

Scallop

Snails

Octopus

MOLLUSK VIDEOS

http://videos.howstuffworks.com/discovery/29082-the-ultimate-guide-octopus-octopus-ancestry-video.htm

http://videos.howstuffworks.com/discovery/29071-the-ultimate-guide-octopus-octopus-sense-of-touch-video.htm

http://videos.howstuffworks.com/discovery/29070-the-ultimate-guide-octopus-octopus-defenses-video.htm

• Organs within a Mollusk– Pair of Kidneys: organs

that remove waste

– Gills: Organs that remove oxygen from water

– Radula: Flexible ribbon of tiny teeth

MOLLUSK ORGANS

• Gills: found in most water-dwelling mollusks

– They are attached to the mantle

– Have a rich supply of blood vessels

– Oxygen from the surrounding water diffuses into the blood and carbon dioxide diffuses out

MOLLUSK ORGANS

– Covered with tiny, hair like structures called cilia.

– The beating movement of the cilia makes water flow over the gills.

• Radula: Flexible ribbon of teeth

– Unique to this Phylum

– Act like sandpaper

– Scrape food from a surface such as a leaf

– May have as many as 250,000 teeth

– The arrangement of teeth are used to classify mollusks

MOLLUSK ORGANS

• What was the 1st evidence of mollusks?– Living in the oceans

about 540 million years ago

– The evidence for this comes from fossil shells in limestone rocks

EARLY MOLLUSKS

• After a mollusk died the shell broke into pieces due to waves and currents.

– The broken pieces piled up on the ocean floor

– The hard materials underwent a chemical change and became cemented together to form limestone

– During this process some shells become fossils

• Based on the presence of:

1. Presence of a shell2. Type of shell3. Type of foot4. The arrangement of

teeth in the radula5. Complexity of the

nervous system

HOW ARE MOLLUSKS CLASSIFIED?

1. Gastropods – most numerous

2. Bivalves

3. Cephalopods

3 GROUPS OF MOLLUSKS

• Gastropod means “stomach foot” – Foot is on the same side of their body as their

stomach

• Snails have a single, coiled shell • Slugs have no shell• Creep along on their broad foot• Some are herbivores, some are scavengers, and

others are carnivores• When a snail is threatened it can pull into its

shell also when it is dry out

GASTROPODS

• Ex: Clams, oysters, scallops, and mussels

• Have 2 shells that are held together by hinges

• Do not have a radula– Instead food sticks to the mucus that

covers the gills– Cilia on the gills then removes the food

BIVALVES

• Found in all kinds of watery environments

– As adults bivalves stay in 1 place or move slowly

– After their larval stage oysters and mussels attach to a surface underwater

– Clams are active and burrow into the sand or mud

– Scallops move from place to place

BIVALVES

• Octopuses, cuttlefish, nautiluses, and squids are all cephalopods

• Tentacles can be 5 meters long

• Capture food with flexible tentacles– Suckers on the tentacles receive taste

sensations– They don’t have to touch something to taste it

• Large eyes and excellent vision

• Swim by jet propulsion

CEPHALOPODS

• Largest and most varied class– Aquatic and

terrestrial• Many marine

snails have poison-tipped mouthparts

– Many serve as an intermediate host for trematode parasites in humans.

– Mantle used as respiratory organ in land snails

CLASS GASTROPODA

– Undergo torsion: movement of the anus• Advantage:

Balance and protection because the head retreats first into the shell• Disadvantage:

Anus is near the mouth• If torsion didn’t

happen the foot would go in before the head

TORSION

• Bivalves – 2 shells

– 2nd largest class of Mollusks

– Marine & Freshwater

– 3 shell layers• Outer protective

layer• Middle layers made

of calcium carbonate

• Inner layer

CLASS BIVALVIA

• Between the mantle and inner layer a pearl is made.

• The pearl is formed by the mucus fluid covering bacteria or a grain of sand that is irritating the muscle.

• They have no radula – filter feeders

• Mussels make pearls – clams do not.

CLASS BIVALVIA

• Minnesota has one of the greatest diversities of freshwater mussels in the U.S.

• Introduced zebra mussel larvae in 1985/1986 to the Great Lakes region from Europe

MUSSELS• Problems: – Outcompete native

mussels

– Disrupt spawning of game fish

– Prolific breeders which damage property

– Settle on native mussels so that they cannot open

– Damage pipelines

• Most complex of all invertebrates

– Octopus: shell is absent

– Squid/ Cuttlefish: Shell is internal

– Nautilus: Shell is external

CLASS CEPHALOPODA

– Large brain: capable of learning

– Image-forming eye similar to vertebrates

– Closed circulatory system

– Blue-ring octopus have salivary glands with venom

CLASS CEPHALOPODA

– Anterior foot is divided into a series of arms

– Marine– Active Predators– Powerful beak-like

jaw and radula