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Phylum Molluska. Mollusks. Non-segmented Bodies Next to Insects, Most Successful Animal. Mollusks are widespread. One of the most successful of all animal phyla. Abundant in marine, freshwater, and terrestrial habitats. All Mollusks Share the Following Characteristics. 1. Body Cavity
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Mollusks • Non-segmented Bodies • Next to Insects, Most Successful Animal
Mollusks are widespread • One of the most successful of all animal phyla. • Abundant in marine, freshwater, and terrestrial habitats.
All Mollusks Share the Following Characteristics. • 1. Body Cavity • 2. Symmetry • 3. Organ System • 4. Three-Part Body Plan
Three-Part Body Plan • Foot • Mantle • Visceral Mass
Characteristics of a Mollusk • Objective: Explain the Evolutionary Relationship Between Mollusks and Annelids. • Both were the first to develop a true coelom. • Trochophore Larva.
Organ Systems of Mollusks • Objective: Describe the Respiratory, Circulatory, and Excretory Systems of Mollusks.
Respiration • Breathe with ciliated gills located in mantle cavity. • Extracts 50% of dissolved oxygen from water. • Some lack gills but mantle cavity functions as simple lung.
Circulation • 3-chambered heart • Open Circulatory System • Only octopi and squids have closed circulatory system.
Excretion: Early developers of an efficient excretory system. • Use coelom as a refuse dump • Nephridia filters wastes • Found in all coelomates except arthropods and chordrates. • Wastes out, molecules in.
Classifying mollusks • Two Shelled: Bivalve • One Shelled: Gastropoda • No Shell: Cephalopods
Section Objective • Describe four classes of Mollusks.
Four classes of Mollusks • There are actually seven different classes of mollusks. But the four major are: • Polyplacophora • Bivalves • Gastropods • Cephalopods
Polyplacophora • This class is one of the smaller classes and still has most of the characteristics of their ancestors. A chiton, of the class Polyplacophora
clam oyster mussel scallop
Bivalves • Bivalves are characterized by two valves (shells), and siphons.
Movement • Bivalves use their foot to dig into the sand. • They may also close their valves rapidly, creating jet propulsion.
Feeding • A bivalve filter feeds by sucking in sea water with one siphon and expelling it out the other.
Respiration • Cilia that cover the gills draws water through one siphon, over the gills, and out the other siphon. • Bivalves also breath with the same gills that they feed with.
Exception • One bivalve, the teredo, doesn’t filter-feed, it digests cellulose in wood using symbiotic protists in its intestine.
Reproduction • Bivalves reproduce sexually. • The reproduce by shedding sperm and eggs into the water. • Bivalves can be either male or female, or the may be hermaphroditic.
Gastropods • They have a pair of tentacles, with eyes on its head • most have a single shell
Gastropoda • The class Gastropoda include snails and slugs.
Movement • A gastropod’s foot is adapted for locomotion. • Terrestrial species secrete mucus to create a path to glide across.
Recognizable Features Eye • Most gastropods have two tentacles where the eyes are located on their head.
Recognizable Features (cont.) • Except for slugs and nudibranchs (sea slugs), most gastropods have a single shell.
Torsion • The visceral mass of gastropods rotate 180 degrees during development.
Respiration • Gastropods respire using gills (aquatic species), directly through the skin or using the mantle cavity as a primitive lung (terrestrial species).
Feeding • Gastropods have many different feeding habits: • Scraping algae off rocks (Radula) • Eating leaves • Eating other animals
Cephalopods • Head-foot
Head-foot • Cephalopods include squids, octopuses, cuttlefishes, and nautiluses. • Most of a cephalopod’s body is a large head attached to tentacles (the foot).
