Transcript Phylum Mollusca - Mr. Lesiuk

BEWARE ! !
BEWARE !
THE MOLLUSCS ARE COMING
Phylum Mollusca
• Very diverse group
• There are 7 classes but we will only discuss
4 of them (Chitons (Polyplacophora),
Cephalopods, Gastropods, Bivalves).
• Some similarities between the groups can
only be seen during development.
• All mollusks have a free-swimming larval
stage in their
development –
The Trochophore Larva
Phylum Mollusca – Body Plan
• Their body plans are very diverse.
• This is why they are the second largest
invertebrate phylum – what’s bigger?
• Major features of the body plans in
mollusks include:
Foot (modified to tentacles in
cephalopods)
Mantle (tissue fold that covers the body)
Shell (internal or external, CaCO3)
Gills (outgrowths of the mantle wall)
Visceral mass (guts)
Radula (rasping tongue)
Chitons
– Eat algae or small animals from the surface of
rocks.
– Live near the shore or even in the deep ocean
– Bottom surface is a muscular foot
– Top surface is made of 8 overlapping plates of
armor.
Gastropods
– Largest group of
mollusks
– Coiled shell
– Some are soft bodied
without a shell
– The foot has a hard
plate (operculum) on
it that protects the
body when it
withdraws into the
shell.
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Clams, mussels, oysters, scallops.
Two shells – “BIVALVIA”
The halves are held together by strong muscles.
Most can’t move – sedentary (except –SC)
Filter feed with gills – food embeds in the
mucus which is moved toward the mouth by
cilia.
– They have a stomach and waste leaves at the
anus – near the excurrent siphon.
– Mussels stick to rocks with a byssus (stringy,
sticky threads)
Cephalopods
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“head footed”
Most complex
Squid, cuttlefish, nautilus, octopi
Nautilus have a complete external shell and many
small tentacles that do not have suckers.
• Octopi have 8 tentacles equipped with suckers,
and they have completely lost their shell.
• Squid have 10 appendages (8 arms + 2 tentacles
with suckers on the tips – feeding). Also have an
internal shell called a pen, that holds the shape of
the body.
NAUTILUS
CUTTLEFISH
OCTOPUS
http://www.youtube.com/wa
tch?v=5rqhomPaxhE
This blue-ringed
octopus has one of
the most poisonous
venoms in the
world. Inhabit the
Great Barrier Reef
along the East
Coast of Australia
Cephalopods
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Dioecious – males and females are separate.
Internal fertilization
Squid lay eggs and die
Octopi will guard the eggs in a cave.
To allow for quick locomotion, the
cephalopods have incorporated a closed
circulatory system.
Cephalopods
• Predatory – unlike the detritus-feeding or filterfeeding molluscs in the other classes.
• Rapid locomotion requires an efficient respiratory
system
• The mantle contracts and pushes jets of water for the
octopus and the squid to move.
• Nautiloids swim with their tentacles.
• Stomach and digestive system.
• Closed circulatory system – vessels
• 2 hearts – one for gill system and one for systemic.
• Highly developed nervous system – brain – octopi can
learn and remember.
• Complex eyes – crucial to a predator.
• http://www.youtube.com/watch?v=jsxAr_yrJtM
Ecological Role
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Wide ecological distribution
Aquatic and terrestrial
Food source for many organisms
Symbiosis
Bivalves recycle sediment
Shells provide homes for other animals when
discarded.
• Some are agricultural pests
• Concentrate pollutants in their tissues (filter feed)