Phylum Mollusca
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Transcript Phylum Mollusca
Phylum
Mollusca
November 3-4, 2014
Chiton
Conch
Clams, Oysters
Nudibranch
Octopus
Squid
General Characteristics
Soft-bodied invertebrates
Unsegmented body, typically bilateral symmetry
Internal or external calcium carbonate shell (usually)
Second largest animal phylum
~ 200,000 species
Show Cephalization
Sensory organs towards one end of body
“head” formation
Habitat/Lifestyle
Sessile-mobile
Benthic-pelagic
Predators-Herbivores-deposit feeders-filter feeders
Typical Body Plan of Mollusks
Three main parts:
Foot
Mantle
Shell
Foot:
On ventral side
muscular; used for crawling,
burrowing, or capturing prey
Can be flat (snails)
spade-shaped (clams)
or modified into tentacles (squid
and octopus)
Abalone
Body Plan of Mollusks
Body covered with
protective mantle:
Thin layer of tissue that covers
most of the mollusk’s body
May or may not produce a
shell
Shell:
made by glands in mantle that
secrete calcium carbonate
Feeding with Radula
Diverse: herbivores, carnivores, filter feeders,
detritivores.
Some use Radula for feeding
Radula: flexible, tongue-shaped structure covered with tiny
teeth
Herbivores use radula to scrape or cut algae;
carnivores use radula to drill through shells or flesh.
Radula
Filter Feeding
Clams, oysters, and scallops filter feed using feathery
gills
Mucus produced by gills traps plankton as water
comes in through siphons
Mollusc Reproduction & Development
Sexual reproduction, external
In tentacled species, fertilization is internal and female lays
fertilized eggs
Most have separate sexes that cross-fertilize eggs
Some hermaphrodites-both sexes
Larval stages
Trochophore larva
Free swimming, ciliated, shell formation begins
Veliger larva
Free swimming
Veliger
Zygote
Trochophore
Juvenile
Adult
Spat
Respiration
Aquatic species use gills
inside mantle to exchange
gases
Incurrent and excurrent
siphon brings water in
Siphon:
Tube-like structure
through which water
enters and leaves
Circulation
Can be open or closed circulatory system
Open system: blood is pumped by simple heart
into sinuses (large saclike space) then to gills, then
back to heart; slower system; found in snails and
clams
Closed system: blood is pumped by heart through
blood vessels; faster system; found in faster-moving
mollusks
6 Classes in Phylum Mollusca
1)Monoplacophora-simple hat shaped shells
2)Polyplacophora----chitons, 8 overlapping shells
3)Scaphopoda-tusk shells
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4) Gastropoda-snails, slugs, nudibranchs, and conchs,
limpets, abalone
4) Bilvalvia - clams, oysters, scallops, and mussels
5) Cephalopoda squid, octopus, and nautilus
Class Gastropoda
“Stomach footed”
molluscs
Have a single shell
(snails) or no shell (slugs)
Class Gastropoda
NUDIBRANCHS
Marine slug
Lacks shell
Class Gastropoda
NUDIBRANCHS
Feed on sponges Cnidaria, algae
Exposed feathery gills
Can be toxic
Retain
undigested
nematocysts from
Cnidaria=Kleptoplasty
Class Bivalvia, Bi-valve = two shells
two-part, hinged shell
Ex: clams, oysters, scallops
mussels
Most sessile, benthic
Most are filter feeders
No head or radula
Burrow
Sand, wood, rocks
A few can use muscular foot that extends from shell for movement
Scallops clap valves together to move
Class Bivalvia
Shell secreted by mantle
Oldest, raised part of shell
called umbo
Have an incurrent &
excurrent siphon that
circulate water over the
gills to remove food &
oxygen
Have heart & open
circulatory system
Class Cephalopoda
Octopus, squid, cuttlefish, & chambered nautilus
Move by using mantle cavity as jet propulsion
Sucks water into mantle cavity, pushes water out of muscular
siphon that can change size (speed) and direction.
Most intelligent mollusk
Well developed head –centralized brain
Large eyes, visual predators
Lack outer shell, very flexible
Active, free swimming predators
Foot divided into tentacles with suckers
Class Cephalopoda
Chromatophores: can change color,
used for camoflauge and social
signaling.
1st group with social signaling-reguires
more complex brain to interpret signals
Use their radula & beak to feed
Closed circulatory system
Highly developed nervous system
with vertebrate-like eyes
Sexual reproduction
Separate sexes with internal fertilization
Class Cephalopoda
SQUID
Largest invertebrate is the Giant Squid
Large, complex brain
8 tentacles 2 arms- longer pair to catch prey
Use jet propulsion
Chromatophores
Have internal shell called pen
Class Cephalopoda
Can squirt an inky
substance into water to
temporarily blind
predators
Class Cephalopoda
OCTOPUS
Eight tentacles
Similar to squid
Sit & wait predators = ambush
Female dies after tending to eggs.
Beak like jaws, radula
Importance of Mollusks
Filter water, healthy waters
Keep algae growth done
Food for top predators and
economically important species.
Used by humans for food
Pearls from oysters
Shells used for jewelry