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Phylum Mollusca (Mollusk)- soft
A. Introductory facts
1. third largest in the animal kingdom,
estimates of 100,000 species
2. Extreme diversity in form (from slugs and snails
to oysters and clams to squid and octopi) and
habitats (terrestrial, marine, and fresh water)
3. Large range in size (includes the largest
invertebrate (giant squid), weighing up to
4,000 lbs. and 60 feet long all the way down
to 0.5 inch long slugs
B. Characteristics of entire phylum
1. ________blastic
2. __________ digestive system
3. ____________ (body cavity w/ membranes)
4. ____________symmetry
B. Characteristics of entire phylum
5. Two part body
connected head/foot
(head contains senses and mouth /foot for locomotion)
visceral mass (section with digestive, respiratory,
circulatory, reproductive organs)
B. Characteristics of entire phylum
6. Mantle tissue
a. often connected to the visceral mass and encircling
much of the body
b. often secretes a shell of calcium carbonate
7. Radula – inside the mouth are rows of rasping
“teeth” on a “tongue” that scrape the food back to
the esophagus
8. An idealized mollusk would crawl on a single flat,
muscular foot, and the body would have a head
at one end and an anus at the other. Above the
body would be an external shell mounted on a
visceral hump containing internal organs.
Class Polyplacophora
Chiton – ancestor
dorsal shell which is
composed of eight
separate shell plates
hinged with one
another which permit
the chiton to bend and
also the animal can
slowly curl up into a
ball
C. Class Gastropoda
1.
2.
(gut – foot)
35,000 species (largest
class & most varied)
Ex.
snail
conch
Cone shells
Sea slug
Welk
3. Torsion – 180` counterclockwise twisting of the
internal visceral organs
Advantage of torsion
Head is withdrawn into mantle cavity first,
then foot (operculum serves as a lid)
Clean water is drawn into mantle from front,
rather than stirred up water from back
Better sensitivity (chemosensory)
Disadvantage
Anus is positioned directly above head
Some species will detorsion 90 so anus is on side
5. Locomotion – use cilia on
mucus trail if small,
muscular waves if larger
6. Feeding –
a. herbivores scrape algae
or eat land plants with their
radula
- Food is trapped in ‘strings’ of
mucus called protostyle
b. a few are predators on
other mollusks, starfish,
jellyfish, sponges, and coral
7. Respiration
siphon – inhalant tube to lungs on land, to gills for
marine
8. Circulatory
- open system w/ heart
- blood used to give
pressure support
9. Hydrostatic skeleton
10. Reproduction
dioecious – marine
monoecious - land
"Giant African land snail"
introduced (non-indigenous species)
considered a serious agricultural pest in the United States.
reach up to 8 inches in length and 4 inches in diameter.
about the size of an average-size adult fist.
have a voracious appetite
known to eat at least 500 different types of plants, including
peanuts, beans, peas, cucumbers, melons, a wide variety of
ornamental plants, tree bark, and even paint and stucco on
houses.
Snails contain both male and
female reproductive organs, and
can lay up to 1,200 eggs per year.
C. Class Bivalvia (two leaves) also know
as Pelicypoda (hatchet – foot)
1.
2.
30,000 species
Ex.
oyster
clam
scallop
mussel
3. Special traits
a. Muscular foot is elongated and narrow (hatchet); used to dig
into the sand to move and to partially bury the animal
b. Shell has two halves (valves)
• Secreted by mantle
• Calcium carbonate
• Hinged
• Opened and closed with a pair of adductor muscles
• Growth increases from the umbro (oldest portion)
4. feeding
• filter feeders
•oysters and clams eat
plankton.
•by pumping water
through their bodies the
mollusks strain the
microscopic organisms
through their gills which
act as sieves.
Bivalve dissection
Part 2
Part 3
5. oddities
a. Some scallops
have multiple eyes
b. biggest bivalve
mollusk is the clam
Tridacna
• native to the IndoPacific
•
reaches a weight of
500 pounds.
c. How do you make a cultured pearl ?
The inside of an oyster's shell is covered with a smooth
shiny coating called nacre, or mother-of-pearl.
an irritant gets caught inside the oyster's shell and it
secretes layers of nacre to protect its body by coating it:
this is the pearl.
Man can force the oyster to produce a pearl by
inserting an irritant purposefully into the shell. It takes the
oyster two to three years to produce a good size pearl.
Cultured pearls are usually not perfect, but the Japanese
have discovered that if you surgically insert an irritant
directly into the body of the oyster this will produce a
perfect pearl.
The largest pearl ever found is reported to be four inches
around and two inches long.
6. reproduction
Dioecious
Marine - external fertilization
Freshwater – internal
Sperm brought in w/ water
Larvae mature in the gill area
and then parasitize fish for
two to three months by
clamping on to their gills or
fins with their valves, then
release.
Enables individuals to travel
far from their parents.
7. Zebra mussel
Non-indigenous (not
native) to U.S.
1985 was accidentally
brought to Great
Lakes in the tanks of
cargo ships from
Europe
Clog water intake
pipes to power plants
and drinking water
supplies
D. Class Cephalopoda (head foot)
10,000 species
2. ex:
1.
Chambered nautilus
squid
Cuttle fish
3. characteristics
Anterior portion of foot modified
into circle of tentacles or arms
Posterior foot has become a funnelshaped siphon
Mantle/siphon used for propulsion
Mantle relaxes, the mantle cavity
fills with water, contraction of
mantle forces water out siphon
When threatened can secrete a dark
ink so that it swim away concealed
Webbed octopus
Reduced shell or no shell (octopus)
Nautilus are only remaining
cephalopod w/ external shell
Squid –internal structure (pen)
Cuttlefish – cuttlebone (used for pet
birds)
Webbed octopus
octopus
Cephalopods are predators that use
tentacles with suction discs to capture
their prey. A radula moves the prey to the
beaklike jaws of the mouth that bite and
crush it. Some cephalopods also secrete
venom into the prey.
attack
color changes
mimic octopus
How intelligent are they?
Cuttlefish: Kings of Camouflage
Dissection walk-through
4. giant squid
Gigantic carnivorous squid a beak-like
mouth powerful enough to cut through steel
cable.
Eyes are the largest in the animal kingdom,
getting to be as big as a basketball (18 inches
across).
nearly 60 feet long, largest invertebrate on
Earth.
suckers help the squid capture its prey and
defend itself against attackers such as the
sperm whale.
Witnessed?
4. giant squid
Giant squids are hunted by the sperm
whale. Many have been seen in battle,
and beaks and tentacles have been
found inside sperm whale's stomachs.
There is at least one eye-witness report
of a smaller whale being drowned by
the giant squid.
Kraken are legendary sea monsters of
gargantuan size, said to have dwelt off
the coasts of Norway and Iceland.
5. Chambered nautilus
•Have a unique shell that closes
off the smaller portions as it
grows (chambered)
•Closed off chambers are filed
with air to help the nautilus stay
bouyant
Nautilus eating a crab