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Snails, slugs, oysters, clams, Scallops & squids.
• includes snails, clams, octopi and slugs
All mollusks share 6 Characteristics
Body Cavity
They have a true coelom, Though it is a small space
Near the heart.
Most mollusks have Bilateral symmetry.
They also have a 3 part body plan.
These parts are the visceralMass, mantle and foot.
All mollusks have organ systemsFor excretion, circulation, Respiration, digestion and
Reproduction.
Many mollusks have 1 or 2 shellsThat act as an exoskeleton.
The shells are made of Calcium carbonate.
All mollusks, except for oysters,Have a radula.
The radula is a tongue like organThat has thousands of teeth.
Mollusks are the only coelomatesWithout segmented bodies.
Mollusks are the first to have Developed an efficient
Excretory system.
The nephridia is used to remove Liquid wastes.
Most mollusks have a 3 chambered heart and
An open circulatory system.
Many mollusks have gills thatAre used for respiration,
Snails have a primitive lung.
Reproduction
• Sexual• External fertilization
• Some hermaphrodites• Some oysters can switch sex
Mollusk Classes
A. Class Gastropoda: Snails & Slugs– single shell (slugs lost it)– large foot on ventral side
Class Bivalvia: Clams, Mussels & Oysters
• two hinged shells
• filter feeders and benthic
• foot used to burrow and anchor
• scallops “clap”
C. Class Cephalopoda: Squid & Octopus
• foot evolved into tentacles with suckers
• active marine predators
• jet propulsion
• radula is a beak
Segmented Worms
Annelid fossils have been found That are 530 million years old!
Scientists think that annelids Evolved from the sea, where
Most annelids are found.
Their size varies from 1mm to More than 3m long!
No matter how long,All segments contain digestive,
Excretory, circulatory, And muscles.
There is a cerebral ganglion,Or primitive brain, in one
Of the first segments and isConnected to a nerve cord
That runs along the bottom Of the worm.
They have septa, which are bodyWalls that separate segments.
They also haveSetae, which are
Bristles thatHelp traction as
They crawl along.
Habitat
• Soil, saltwater and freshwater
• Closed circulatory system
Respiratory System
• Gas exchange through body wall
Cuticle
Digestive System
• “Tube within a tube” digestive system
• Mouth• Pharynx• Esophagus• Crop• Gizzard• Intestines • Anus
Reproduction
•Hermaphrodites
•Sexual
• Clitellum -- cocoon