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Mollusca
Mollusca
• CHARACTERISTICS:
• Mollusks are soft bodied animals that usually
have an internal or external shell
• 4 Main body parts
– foot – crawling, burrowing and tentacles for capturing
prey
– mantle – thin layer of tissue covers most of the
mollusks body, like a cloak
– shell – made by glands in the mantle that secrete
calcium carbonate
– visceral mass – contains internal organs
Characteristics cont.
• herbivore, carnivore, filter feeder, detritivores, parasites
• radula – flexible tongue shaped structure which
hundreds of tiny teeth are attached. (scrap algae or dig
through shell)
• siphon – tube like structure through which water enters
and leaves the body
• marine mollusks – gills
• land mollusks – use mantle cavity (oxygen diffused over
membrane)
• open circulatory system – blood is pumped through
vessels by a simple heart
• closed circulatory system – (octopi, squid) – can
transport blood more quickly
• release nitrogen containing waste – ammonia
Bivalvia
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– any mollusk that has a shell divided
into 2 valves hinged at one side
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Examples – clams, oysters, mussels,
scallops
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Characteristics
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shell made of calcium carbonate
most dioecious – separate sexes, some can alter
gender, external fertilization
most obtain food and oxygen by filter feeding siphon
system
no head, teeth or eyes
• Most of the time all we
see of most clams is
simply a siphon
protruding from the
sediment or a coral
head. Several
different types of
siphons are found,
however, and experts
can sometimes tell the
clam species in a
given area simply by
observing the siphon.
Clam Anatomy
Bivalvia Char. Cont.
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strong muscular foot used for burrowing or locomotion
open circulatory system
feeds on plant cell material
use sticky threads to attach themselves to rocks
can use shell by rapidly flapping their shells when
threatened
some scallops have dozens of eyes?
adductor muscles used to close and open shell
no radula
Labial palps – on either side of the mouth, sort filtered
food particles
gills
oldest part of shell – umbo
Scallop eyes
• Many people know of scallops as a tasty seafood, but
most have never seen a living scallop. Scallops are
diverse, with over 300 species of scallops living on the
ocean floor worldwide. They range from shallow
waters to areas several hundred feet deep. Scallops,
classified as bivalve mollusks, hide some amazing
secrets. For one, about sixty primitive tiny bright blue
eyes eyes reside in rows along a scallop’s mantle
edge to detect motion, light and dark. A scallop can
easily regrow any lost or injured eyes. Although these
eyes may or may not produce clear images, the ability
to sense an object moving with the speed of one of the
scallop’s predators allows the scallop to save its skin
(or to be scientifically correct, its shells) by either
shutting immediately or swimming away.
Scallop eyes
eyes
• Secondly, scallops possess an unusual trait which
most other bivalves lack: the ability to swim. Scallops
can propel themselves away from danger by
contracting their powerful muscles and "clapping" their
shells together, forcing water out through openings on
both sides of their shell hinge. They can move
forwards backwards, make turns, and right themselves
in this fashion. Scallops swim particularly when faced
with a predator (e.g., a seastar). Otherwise, if left
relatively undisturbed, scallops are fairly sedentary
creatures that lie on the seafloor as they feed by
filtering microorganisms from the water.
• Those tasty cylindrical or disk-shaped morsels of
scallop meat found in seafood shops are the adductor
muscles that in the living scallops make their unique
swimming ability possible.
CLAM ANATOMY
• 1. This is the clam's left
mantle. The mantle
secretes the shell and is
attached to it along the
pallial line seen on the
inner surface of an empty
valve. Note: the left
mantle was detached
from the left valve when it
was removed. The black
arrows show the border
of the left mantle
CLAM ANATOMY CONT.
• 2. This is the anterior
adductor muscle, a
major muscle for
closing the valves
• 3. This is the
posterior adductor
muscle, a major
muscle for closing the
valves.
CLAM ANATOMY CONT.
• 4. This is the pericardial
cavity, a region covered
with a thin, dark
membrane that contains
the heart, kidney, etc.
• 5. This is the margin of
the right mantle. The
right and left mantles join
together to form the
incurrent and excurrent
siphons
• 6. This is location of the
incurrent and excurrent
siphons.
Scaphopoda
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– shovel foot
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Examples – Tusk shells
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Characteristics
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live only in salt water
external fertilization
shells shaped like long thin fangs
draws water in through small tip of shell that sticks out
of the sand or mud. Water flows into the mantle cavity
where oxygen is absorbed directly into the blood
size 2mm – 15 cm
shell open at both ends
no gills, eyes, heart, or blood vessels (open circulatory)
radula – tooth, grinds up food
Tusk shell
Cephalopods
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– head foot
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Examples – Octopus, squid, cuttlefish, and
nautilus
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Characteristics
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nautilus – up to 90 tentacles, no suckers, but contain
sticky mucus like covering
» sexual reproduction
» male has 4 tentacles that form a spandex –
transfers sperm
» carnivores
» primitive eyes
» jaw/radula
» siphon – bent tube through which fluid can be
drawn over the edge of one container into a lower
container by means of air pressure
Cuttlefish
NAUTILUS
• Nautilus are primitive
cephalopods and are true
living fossils. They are
normally found in cool
deep waters off of coral
reefs, and require the
high pressures in deep
water for both good
health and successful
growth, and as such they
have no place in home
aquaria. They are subject
to a fishery for their shells
and recently over 10,000
of them were collected
around New Caledonia in
a few months. This
effectively destroyed one
population of them.
Cephalopoda cont.
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most highly developed of all mollusks, large brain
dioecious
males of specialized tentacles to transfer sperm
modified foot – tentacles
gills
excellent eyesight
cephalo – head
poda – footed type animal (divided into tentacles or
arms)
– swim rapidly
– chromatophores – allow animals to change colors and
patterns
Squid anatomy
Giant squid video
• Scientists capture giant squid on camera Science - MSNBC.com
Cephalopoda cont.
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teeth like hooks can dig into a shell/ radula, carnivores
digestive system is muscular
propulsion system used to move and keep water out
octopus is the only cephalopod that doesn’t have a shell
– others have small internal shells , nautilus – external
shells
closed circulatory shell
bronchial hearts – each cephalopod contains two hearts
working as one
squid eaten by sperm whales
squid 17 meters – 6,000 Ibs.
octopus and squid shoot out ink when attacked
Polyplacophora
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– poly = many, plac = plate, phora =
carry, ie: bearer of many plates
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Examples – Chitons
•
Characteristics
– 8 piece segmented shell, bilateral symmetry
– inhabit rocky shorelines and shallow ocean
bottoms
– rolls itself in a ball for protection
– will create a vacuum for protection, to hold
chiton in place
– move in same fashion as snails, foot secretes
small amount of mucous
Cont.
– eat seaweed and algae
– only a few centimeters long, 8mm – 33cm
– gills for respiration
– closed circulatory system
– poorly developed ganglia
– nephridia – primitive kidney for excretion
– dioecious, external fertilization
– radula used to scrap algae
Polyplacophora
• A worm-like chiton from
the South Pacific. Most
chitons have welldeveloped, easily visible
dorsal plates, but in a few
species the plates are
greatly reduced. A few of
these species also have
an elongate, worm-like
body. Shown here are an
adult, a juvenile and a
young chiton.
• Light microscope
photograph of
Rhyssoplax radula
showing magnetitetipped (black)
tricuspid teeth
Gastropoda
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– stomach foot
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Examples – Pond snail, limpets, abalones,
land slug, and whelks
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Characteristics
– single shell carried on back
– broad foot crawls across the rocks or digs into
the sand
– spiral shell
– shell is protection for animal
– some retreat into the shell and close by using
Operculum – plate attached to foot, allows
them to withstand long periods of dryness
Gastropoda cont.
– some have modified foot for swimming and
used for reaching
– pteropoda – winged feet
– some have no shell – some squirt ink for
protection, taste bad or poisonous
– opisthobranchiata – sea slug, lose shell by
adult
– sea hares are hermaphrodites
– some can seal shell and with stand long
periods of dryness
– radula
Snail Anatomy