Molluscs - SchoolNotes
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Transcript Molluscs - SchoolNotes
Molluscs
Phylum Mollusca
Includes snails, clams, octopuses and
others.
There are more species of molluscs in the
ocean than any other animal group.
There are 200,000 species of molluscs.
Mollusk Structure
Have soft bodies enclosed in a calcium
carbonate shell.
Mantle- thin layer of tissue that secretes
the shell.
Bilaterally symmetrical.
Ventral, muscular foot used for locomotion.
Head with eyes and other sensory organs.
Radula- ribbon of small teeth used to feed
by rasping food from surfaces.
Radula made of chitin.
Gills for gas exchange.
Types of Molluscs
They occupy all marine environments from
the wave-splashed rocky shores to
hydrothermal vents.
Gastropods (Class Gastropoda)
Largest, most common, and most varied.
Snails are most familiar.
Also includes limpets, abalones, nudibranchs.
75,000 species.
Most are coiled mass of vital organs enclosed by
a dorsal shell.
Shell rests on a ventral creeping foot.
Gastropod means “stomach foot.”
Limpet
Abalones
Nudibranch
Nutrition
Most use radula to scrape algae from
rocks, like periwinkles, limpets, and
abalones.
Some like mud snails are deposit feeders
on the bottom.
Whelks, oyster drills, and cone shells are
carnivores that prey on clams, oysters,
worms and small fish.
Whelks
Oyster Drill
Cone Shell
The violet snail Janthina has a thin shell
and produces a bubble raft out of mucous
to float on surface and look for its prey.,
Sea hares Aplysia have smal, thin shells
buried in tissue that graze on seaweeds.
Janthina floating
Aplysia
Bivalves (Class Bivalva)
Clams, Mussels, Oysters
Body is laterally compressed (flattened
sideways) and enclosed in a shell with two
parts or valves.
No head and no radula.
Folded and expanded gills used to obtain
oxygen and filter small food particles.
Mantle lines the inner shell.
Strong muscles close the valves.
Clams
Use shovel-foot to burrow in sand and
mud.
Water is drawn in through a siphon
(snorkel).
This allow them to get oxygen even when
buried in the sand.
Geoduck Clam
Mussels-Secrete byssal threads that attach
on rocks and other surfaces.
Oysters-cement their shell to a hard
surface.
Pearl oysters- form pearls when the oyster
secretes calcium carbonate to coat
irritations in mantle
Green lipped mussel
Oyster with pearl
Many bivalves bore in coral, rock, or wood.
Shipworms-fouling organisms that settle
on to bottom of boats, pilings and cause
these to deteriorate.
Shipworms
Cephalopods (Class Cephalopoda)
Predators that include octopuses, squid,
cuttlefish.
Nearly all are agile swimmers.
Have complex nervous system and a
small or no shell.
650 marine species.
Cephalopod means “head-foot.”
The food is modified into arms and
tentacles, usually with suckers used to
capture prey.
Have large eyes on the side of head.
Octopuses- round body
Squids- elongated body
Protected by a thick and muscular mantle.
Squidward
Have two or four gills on head and water
enters and leaves through a siphon
(funnel).
Swim by forcing water out of mantle cavity
through the siphon.
Use jet propulsion with siphon to move in
any direction.
Octopuses
Have eight long arms and lack a shell.
Common bottom dwellers.
Size varies from 5cm (2in) to 9m (30ft).
Efficient hunters of crabs, lobsters, and
shrimps.
Bite prey with a beak-like jaw. Radulas
rasp away flesh.
Secrete a paralyzing substance and some
have a toxic bite.
Make their homes in crevices, bottles,etc.
They distract predators by emitting a cloud
of dark fluid produced in the ink sac.
Octopus
Squids
Better swimmers than octopuses.
Elongated body covered with mantle has
two triangular fins.
Use jet propulsion and can move forward
and backward.
Eight arms and two tentacles with suckers
around a mouth.
Shell reduced to a pen on upper mantle.
Size varies from few centimeters to largest
living invertebrate 60ft!
Cuttlefish
Have eight arms and two tentacles.
Flat bodies and fin on the sides.
Have calcified internal shell that aids in
buoyancy.
Shell called cuttlebone.
Cuttlebone sold as a source of calcium for
cage birds.
Cuttlefish
Chambered Nautilus
Coiled, external shell with gas-filled
chambers that serve for buoyancy .
Body in the outer chamber has 60-90 short
suckerless tentacles to capture prey.
Chambered Nautilus
Chitons (Class Polyplacophora)
800 species
Have 8 overlapping shell plates on dorsal
surface.
Internal organs not coiled.
Live on shallow, hard bottoms using radula
to feed on algae.
Chiton
Scaphopds (Class Scaphopoda)
Tusk shells.
Elongated shell open at top and tapered
elephant-like tusk
Live on sand or muddy bottoms.
Have thin tentacles with adhesive strips to
capture foraminiferans.
Tusk Shells
Feeding and Digestion
Use salivary and digestive glands that
release enzymes to break down food.
Bivalves have crystalline style that
secretes enzymes in the stomach.
Have open circulatory system where blood
flows out of vessels and into the body
cavity.
Cephalopods have closed circulation.
Nervous System and Behavior
Gastropods and bivalves have gangliaclusters of nerve cells.
Octopuses have a brain that allow for
learning .
When preyed upon some release ink and
can change color.
Reproduction and Life History
Most have separate sexes.
Some are hermaphrodites.
Bivalves release sperm and eggs in the
water.
Cephalopods mate and use a
spermatophore (modified arm) to transfer
a packet of sperm.
Males have a long, flexible penis.