Download 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