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Phylum Molluska
C-27-4
Phylum Molluska
•1. Soft bodies
•2. Foot
•3. Mantle
•4. Most have shells
Molluska Classes
• Gastropods – mollusk with ONE
shell
• Bivalvia- mollusk with TWO
shells
• Cephalopoda – mollusk with and
internal shell or no shell at all.
Exception chambered nautilus
I. Characteristics
• A. Coelomates – True
coelom, a hollow fluid filled
cavity surrounded by a
mesoderm, body wall of
muscles That are separated
from the gut and can aid in
blood transport.
• B. Trochophore – Larvae stage
1. Mollusca – body plan
A. All have similar body plans – foot,
soft body, mantle and shell
B. Foot is a soft muscular structure,
used for movement.
C. Radula- Flexible tongue like
structure present in snails and slugs,
used to scrap food off of leaves.
D. Visceral Mass – Body area that
contains all the mollusks organs
C. Mantle is a thin delicate layer of
tissue that surrounds the body, and
secretes a calcium carbonate shell.
E. Shell - also called valves and is
secreted by the mantle.
1. 3 Layers
a. Inner – smooth, protects
soft body.
b. middle- calcium carbonate,
strength
c. Outer – protects shell
against sea environment.
2. Feeding
A. Much variation, carnivores, herbivores,
filter feeders, detritus feeders, scavengers
or parasites
3. Respiration
A. Aquatic mollusks exchange gases
through gills and through exposed wet
skin.
B. Terrestrial mollusks usually exchange
gas through a specialized adapted
mantle cavity.
4. Circulation
A. Open circulatory system for
clams and oysters. Fluid called
hemolymph that moves through
channels and pools into tissues
spaces called hemocoel where
organs are bathed
B. Closed circulatory system for
fast moving animals, vessel driven.
5. Excretion
A. Solid waste passes out through the end of
the gut, anus.
B. Nitrogen waste are removed from the blood
by organs called nephridia.
6. Nervous systems
A. Clams and relatives have few ganglia
(cluster of nerves )and nerve cords.
B. Octopus and relatives have well-developed
brains, excellent vision, touch and taste
7. Reproduction
A. Some mollusks are hermaphrodites, some
external, some internal.
8. Classes:
A. Gastropods
1. Examples –
snails, slugs, abalone, sea hares nudibranchs
2. One shell is used for protection or no shell.
3. Torsion –process where the visceral
mass twists bringing organs to the front of the animals
body.
4. Non shelled animals use poison or are bad
tasting
B. Bivalves
1. Examples – clams, oysters, mussels, and
scallops
2. 2 shells present for protection
3. Shells are hinged together with strong muscles
called adductor muscles.
4. Some produce nacre (mother of pearl)
• 5. Siphons – filter feeders use
fleshy tubes that extend
outside and between the
shells.
–A. Incurrent siphon – Pulls
water in filled with nutrients.
–B. Excurrent Siphon –
Release waste.
6. Feeding in Bivalves
• A. Gills – water enters through
incurrent siphon, food gets
caught on sticky mucus on
gills. Food is than moved to
the mouth to indest. ( MUCUS
FEEDERS)
C. Cephalopods = “head” “footed” animals
1. Examples – chambered nautilus, octopus,
squid, and cuttlefish.
2. Largest, most active and most intelligent
3. 8 tentacles and 2 arms = 10 appendages (squid,
cuttlefish) - 8 arms (octopus)
4. Suckers found on tentacles.
5. Internal shells or no shell, exception, (Nautilus)
6. Ability to change color, Chromatophore
pigment.
7. Some squirt ink, defense.
8. Beak – powerful jaws for eating.
Giant Australia Cuttlefish