Transcript Mollusca - Ms. Marcos` Biology Wiki

Phylum Mollusca
Soft-bodied
animals!
3 Classes of Molluscs
GASTROPODA : includes
limpets, snails, slugs
and whelks
BIVALVIA: includes clams,
oysters, mussels, scallops
and shipworms
CEPHALOPODA: includes
octopi, squid, cuttlefish,
and nautilus
Above: Limpet
Above: Scallop showing off its
eyes!
Left: Cuttlefish and squid
All forms of Molluscs have a body with three parts:
1.
Visceral Mass
- The soft bodied portion that
contains the internal organs
2.
Foot
-
3.
A strong, muscular portion
used for moving (or tentacles
in cephalopods)
Mantle
-
A covering that goes around
the visceral mass
Can secrete a shell
Find the
Foot,
Visceral
Mass and
Mantle!
A diverse phylum
► Mollusca
contains 80,000 different species
► Symmetry: Bilateral
► Level of Organization: Organ
► They also have a well developed nervous system,
a circulatory system, and a brain.
 Cephalopods have a closed circulatory system (e.g.
squid, octopus…)
 Bivalves and Gastropods have an open circulatory
system (e.g. clams, snails…)
► Feeding:
 Complete digestive tract
 Most have a radula – a sharp “tongue” like a
nail file that they use to rasp at food
 Feeding strategies differ between the classes
► Excretion:
 Complete excretory system with an anus
 Simple kidneys
► Reproduction:
 Sexual with internal fertilization
 Most have separate sexes, although snails are
usually hermaphroditic
Class Bivalvia
► Two
valves (shells), e.g. mussels, clams, oysters
► They have a muscular foot for digging
► They often attach to the substrate with byssal
threads that hold them in place
► Some, like scallops, can swim
► Siphons
(tubes to carry water into and out of the
animal)
► A muscle holds the valves (shells) together
► No head, radula or true eyes (eyespots only)
► Gills for getting oxygen from the water
► Open circulatory system
Above left: Elephant trunk
clams, named for their large foot
Above right: an opened oyster
commonly enjoyed raw or cooked
as a delicacy
Lower right: Scallop showing off
its many primitive eyes
Giant clams have zooxanthellae,
just like corals
Class Gastropoda
► Gastropod
means
stomach-foot
► They usually have one
shell, e.g. snails
► They have a variety of
feeding methods – some
are herbivores, some
carnivores, some parasites
► Some cone snails inject a
venom that can be fatal to
humans
► Snails
have a hard “door” called an
operculum
► Internal fertilization and are often
hermaphrodites
► Use a radula for feeding
Gastropod Diversity
Also in Class
Gastropoda…
The
Nudibranch!
► Nudibranch
means “naked
gills”
► They have
evolved to have
no shell
► Toxic
and have bright
beautiful colors as a
warning to predators
► The
feathery parts on their backs are their gills
► Two rhinophores that “taste” the water around
them to sense their environment
Top 5 reasons why Nudibranchs are
so cool…
► 5.
They are amazing colours…
► 4. They can eat toxic sponges without being
harmed, but can transfer the toxin to a
predator if bitten
► 3. Hermaphroditic nudibranchs battle to be
the one to inject the other with sperm.
► 2.
They can eat nematocysts from corals and
anemones without getting stung. The next thing
that touches them gets the sting!
► 1. A nudibranch can eat algae and take the
chloroplasts into its own body. It can then perform
PHOTOSYNTHESIS!
Class Cephalopoda
► Their
name
means
“head – foot”
► E.g.
Octopus,
squid,
cuttlefish
► They
have 8 (or more) arms
► They can push a jet of water out their
siphon, allowing them to move quickly
► An ink sac allows them to eject ink as decoy
► The
Nautilus has a shell
with chambers that
allows it to change depth
easily (they are great
hunters)
► Many
cephalopods
have no shell
 Squid and cuttlefish
have a hard part inside
 Octopus have no hard
parts except for their
mouth
► Cephalopods
have a very well developed
nervous system
►nerves can carry messages TEN times faster
than in humans
► Their
eye is complex and has 180 degree
vision out of the sides of their heads
head
eye
liver
beak
stomach
siphon
heart
tentacles
suction cups
kidney
inksac
► They
have a developed brain and can solve
problems
► Mouth is called a beak
► They
have internal fertilization and have
separate sexes
 male has a special tentacle used to put sperm
packets inside the female
 Squid mate in a big group
 Female octopus lay thousands of eggs in a cave
and guards them until she dies
Octopus
Octopus beak
Swimming Octopus
Octopus on the beach
Octopus arm in detail
► Many
have photophores that allow them
to produce light
► Most also have chromatophores that
allow them to change color to match their
background
Squid
Caribbean Reef Squid
Calamari: a deep fried squid dish
Tentacles of a giant squid
Squid eye and gills
Squid Fact
The largest squid ever caught was a 10 m long
Colossal Squid off the coast of New Zealand and
weighed in at 495 kg. Colossal Squid are larger than
the giant squid found off the Mexican coast and are
thought to grow in size to 13 meters!