Transcript Mollusks and Echinoderms

Mollusks
Biology
Jones
Mollusks
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Term Mollusk means soft
Phylum called Mollusca
Over 47,000 species
Large range in size from tiny snails of 5
mm to giant squid 66 ft. long
• Can live both in sea and fresh water and
on land.
Characteristics of Mollusks
• 3 distinct body parts: head, foot, and
visceral mass
• Soft body parts are covered by a sheet of
tissue called a mantle.
• Head contains mouth and sensory organs
• Some have a toothed organ called a
radula which the mollusk uses to scrape
off bits of plant or animal matter that the
animal uses for food.
Characteristics Cont.
• The foot is a muscular structure that clams and
some other mollusks use for burrowing into
sand.
• The visceral mass contains digestive, excretory
and mouth.
• The mantle covers the visceral mass and
secretes the shell.
• Gills that function in respiration are located in
this mantle cavity in aquatic mollusks. Land
forms usually have a mantle that is modified as a
respiratory surface.
Mollusk Classes
• The 3 major classes are :
– Bivalvia (means “two shells”)
– Gastropoda (means “stomach foot”)
– Cephlapoda (means “head foot”)
Mollusks with 2 shells
• Clams oysters, and scallops belong to a
class of mollusks that have 2 shells hinged
together.
• The animals themselves are referred to as
bivalves.
Clams
• Most live in the sand or mud at the sea
bottom , some live in fresh water
• Shells are secreted by the edges of the
mantle and growth rings are often
apparent on the shells.
• The shells are held together by ligaments.
2 powerful adductor muscles function to
close the shells.
Clams Characteristics Continued
Sensory nerves
• Clams can withdraw completely into their
shells.
• Clams have no head and no radula, have
poorly developed sensory structures.
Structures along the edge of the mantle
respond to light and touch.
• Masses of nerve cells called ganglia are
located above the mouth and in the foot.
• Ganglia are connected by nerve cords
More clams
• Obtain both food and O2 from the water that
flows through their bodies.
• Water enters the clam through the incurrent
siphon Cilia move the water across respiratory
organs, called gills in the mantle cavity.
• O2 diffuses from the waste to the blood and
CO2 diffuses from the blood to the water.
• The water is then expelled through the
excurrent siphon.
Clams
• Known as filter feeders.
• Mucus on the gills traps the food matter,
cilia push the food-laden mucus on to the
clam’s mouth.
• From there the food passes into the
stomach.
• Undigested food particles leave the clam
through the anus.
Clams
• Open circulatory system
• Blood flows through large open spaces or sinuses, rather
than through a system of blood vessels.
• Clams have a 3 chambered heart that pumps the blood
through the clam
• Most clams have separate sexes. The sperm and eggs
are shed into the water (external fertilization), where
fertilization takes place.
• The fertilized egg becomes a trochophore larva that
settles on the bottom and develops into an adult.
Oysters
• Cannot move, are sessile.
• Early in its live, an oyster permanently attaches
its flat lower shell to a hard surface.
• The outer shell is rough in texture, while the
inner surface of the shell is smooth and often
iridescent.
• If an irritant such as a grain of sand enters an
oyster shell, the oyster protects itself by covering
the foreign matter with several layers of shell
material. Called a pearl.
Oysters
Mollusks with one Shell
• Largest class called Gastropoda, a
name means “belly(stomach)footed”
• 37,500 species include snails and
slugs that live in water and on land.
• Most are univalves, only one shell.
• Shell is usually coiled, slugs have no
shell.
Slugs
• Can survive without shells because they
live in moist environments.
• Like land snails, slugs that live on land
respire through blood vessels in the
mantle cavity.
• Sea slugs respire through gills.
Head-Foot Mollusks
• Class Cephalopoda includes the more advanced
of all mollusks—the squid, octopus, cuttlefish,
and nautilus
• Cephalopod mans “head-foot and reflects the
fact that the head and foot of these mollusks is
fused during development.
• Well-developed head bears a pair of complex
eyes and the foot is divided into tentacles.
• Only the nautilus has an outer shell.
• The octopus has no shell at all
Cephalopods
• Cephalopods have a well-developed nervous
system with many ganglia and a complex brain
Central mouth has jaws and a radula and is
surrounded by arms or tentacles.
The nautilus has over 90 tentacles, the octopus
has eight, and the squid has 8 tentacle-like arms
and 2 long tentacles.
• Powerful suckers on the arms and tentacles of
most cephalopods aid in grasping prey. Some
cephalopods, such as the giant squid, have
suckers that are armed with hooks.
Cephalopods
• All are marine animals and live at all
depths.
• Cephalopods are predators—that is they
kil and eat other animals, such as fishes,
crabs, and bivalves.
Octopus
• The octopus is highly specialized for its
predatory way of life.
• Moves by jet propulsion forcibly
contracting the muscles of its mantle and
closing the mantle cavity, the octopus
squirts out a jet of water through its siphon
and speeds off in the opposite direction.