37-1 mollusks invertebrates like clams, snails, slugs and octopuses phylum mollusca 112,000...
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37-1 Mollusks
Invertebrates like clams, snails, slugs and octopuses
Phylum mollusca
112,000 species. Some are predators, others are filter feeders
Have bilateral symmetry
Common Features
Coelomates
Have a true coelom (hollow fluid filled cavity)
Advantage is muscles of body wall are separate from those of the gut, so body wall muscles can contract without hindering the digestion process. Also transports blood
Trochophore Shared by aquatic
mollusks and annelids during the larval stage
Contains cilia at both ends and in the middle
Cilia contribute to dispersal of trochophore
Body Plan of Mollusks
2 regions 1.Head-foot 2.Visceral mass 1. Head-foot (fig. 37-2) head, mouth, sensory structures,foot for locomotion 2. Visceral mass (fig. 37-2) heart, digestive organs, excretory organs,
reproductive organs
Mantle Covers visceral mass, which secretes 1 or
more hard shells made of calcium carbonate. Found in both sexes. Protects entire animal. The disadvantage is that the animal cannot exchange gases, so they had to evolve gills, which exchange gases with water. The gills are protected by the mantle cavity.
Ganglia Located in the head-foot
region Connected by 2 pairs of
nerve cords
Radula A feeding adaptation. It is
a flexible, tongue-like strip covered with abrasive teeth. (fig. 37-3)
3 Classes of Mollusks
1. Gastropoda Snails, abalones, conchs 2. Bivalvia Clams, oysters, scallops 3. Cephalopodactopuses, squids, chambered nautilus *Only mollusk to have closed
circulatory system
1. Class Gastropoda
Body undergoes torsion during larval stage. The visceral mass twists 180 degrees towards head, so everything like gills, mantle cavity and anus are near head. (fig. 37-4)
Have open circulatory system. A circulatory fluid called hemolymph passes through body into tissue spaces called hemocoels then the hemolymph goes back to the heart.
Class Gastropoda Snails (land and
aquatic, fresh water and salt water)
Aquatic snails respire through gills
Land snails respire through mantle cavity and are hermaphrodites
Move around for food
Abalone
Conch
2. Class Bivalvia
Shell is divided into 2 halves (or valves) connected by a hinge
Use adductor muscles to close shell
Has open circulatory system
Valves Each valve contains 3 layers of cells
secreted by mantle
a. Outer layer protects shell against acidic conditions
b. Middle layer is calcium carbonate
c. Inner layer is smooth and protects soft body. This is what forms a pearl.
Bivalves Bivalves are sessilehey use muscular foot to dig into sand
and become filter feeders Only mollusk not to have a radula Have 3 pairs of ganglia (nerves) *near mouth *near digestive tract *near foot
Clams
Buried in mud or sand Use siphons 1. Incurrent siphon allows food to enter,
sticks to mucus on gills which enters mouth. Gases are also exchanged and sperm also enters here.
2. Excurrent siphons allow all waste materials to exit the clam
Reproduction
Reproduction in fresh water clams vs. salt-water clams
1. Fresh water
Sperm enters incurrent siphon and fertilization is internal
2. Salt-water Egg and sperm are released into the water.
Fertilization is external.
CephalopodaChambered
Nautilus
Show videoHand out clam terms and
clam anatomyDissect clam and define all
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