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Mollusks and Echinoderms
Section 1 – Mollusks
(Gastropods, Bivalves,
and Cephalopods)
Mrs. Donna Gentile – September, 2014
Characteristics of Mollusks
 Examples:
clams, oysters,
scallops, snails, squids
 Invertebrates with soft,
unsegmented bodies that are
often protected by a hard outer
shell.
Characteristics of Mollusks – cont.
Thin layer of tissue called a mantle
that covers its internal organs
 Biologists classify mollusks into
groups based on their physical
characteristics: shell, type of shell,
type of foot, type of nervous system

Body Structure
 Bilateral
symmetry
 Digestive system with 2
openings
 Body parts are not repeated –
internal organs are located
together in one area
Circulatory System
 Most
have an open Circulatory
System – blood is not always
inside blood vessels
 Blood sloshes over the organs
and returns to the heart
Obtaining Oxygen
Most mollusks that live in water have
gills
 Gills have cilia and a rich supply of
blood vessels
 Carbon dioxide, a waste gas, moves
out of the blood and into the water

Snails and Slugs
 Gastropods
are the largest group
of mollusks
 Live in oceans, rocky shores,
fresh water, on land
 Have a single external shell or no
shell at all
Obtaining Food
 Some
are herbivores,
scavengers, carnivores
 Use a radula to obtain food
 Herbivores – sandpaper to tear
through plant tissue
 Carnivores – drill a hole, scrapes
Movement
 Creeps
along on a broad foot
 Foot oozes a carpet of slippery
mucus which helps make it
easier for the gastropod to
move
Two-Shelled Mollusks
Bivalves – are mollusks that have 2
shells held together by hinges and
strong muscles
 Examples: oysters, clams, scallops,
mussels
 Found in all kinds of watery
environments

Obtaining Food
Filter feeders that strain tiny
organisms from water
 Capture food as water flows over
their gills, food sticks to the mucus
that covers the gills, cilia move the
food particles into it’s mouth
 Most bivalves are omnivores

Movement
 Don’t
move quickly
 Larvae – float or swim Adults –
stay in 1 place or use their foot
 Oysters and mussels attach
themselves to rocks
 Clams move
Protection
 Sand
gets stuck between a
bivalve’s mantle and shell – it
irritates the soft mantle –
mantle produces a smooth,
pearly coat to cover the object
 Sometimes a pearl forms
Octopuses and Their Relatives
 Cephalopods
are ocean-dwelling
mollusks whose foot is adapted to
form tentacles around its mouth.
 Examples are:octopuses, squid,
nautiluses, cuttlefishes
Obtaining Food
Carnivores - uses tentacles to
capture the food and crush it
 Tentacles have suckers that receive
sensations of taste and touch
 It doesn’t have to touch something to
taste it because the suckers respond
to chemical in the water – tastes
before touching it

Nervous System



Large eyes – excellent vision
Most complex nervous system of any
invertebrate
Large brains – can remember and learn
Movement
 Swim
by jet propulsion
 Squeeze a current of water out of
the mantle cavity and through a
tube
 Turning the tube changes the
direction they’re going
Echinoderms
Section II
Characteristics of Echinoderms





Examples: Starfish, sea cucumber, sea
urchins
Marine dwelling
Invertebrates
Spiny skin
Able to REGENERATE – regrow missing
parts
Body Structure



Endoskeletons
Penta-radial symmetry
Endoskeletons
Circulatory System



Network of fluid-filled canals that function in gas
exchange, feeding and in movement.
Contains a central ring and areas which contain
the tube feet The tube feet poke through holes
in the skeleton and can be extended or
contracted.
They do not have a true heart and the blood
often lacks any respiratory pigment (like
hemoglobin).
Obtaining Oxygen


Echinoderms have a a poorly developed
respiratory system.
They use simple gills and their tube feet to
take in oxygen and pass out carbon
dioxide.
Obtaining Food



Majority are carnivores – feed on sponges
& mollusks
Stomach is flipped out of mouth and
surrounds soft body parts of prey.
Digestive juices are secreted and liquefy
prey.
Mouth, stomach, digestive gland & anus
Movement



When echinoderms move in a manner such as
walking or crawling, they pump sea water
through a series of internal body canals.
The water is used to inflate some of the tube
feet, causing them to expand. In many species,
the tube feet are equipped with suckers that grip
onto the sea floor.
The feet hold tight to the bottom as muscles
within the feet contract, enabling the animal to
propel itself.”
Nervous System



Echinoderms do not have brains, they
have nerves running from the mouth into
each arm or along the body.
They have tiny eyespots at the end of
each arm which only detect light or dark.
Some of their tube feet, are also sensitive
to chemicals and this allows them to find
the source of smells, such as food.