1. Coelomate Protostomes
Phylum Mollusca
Phylum Annelida
Phylum Arthropoda
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2. Protostomes Three major phyla share three embryonic characters
Spiral cleavage
Mouth develops at site of blastopore (1st mouth)
Mesoderm develops from lips of blastopore as solid masses, splits
“split” coelom
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3. Protostomes Formation of Mesoderm and Coelom
Solid masses of mesoderm separate from lips of blastopore.
Split opens in mesoderm to form “split” coelom
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4. Phylum Mollusca Phylum Mollusca (Greek “soft”) Body plan
~100,000 species, 2nd largest phylum
Body plan
Tube-in-tube, Protostomous
Bilateral symmetry
Coelomate, “split” coelom
Marine, aquatic, terrestrial
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5. Phylum Mollusca Body with three parts Visceral mass (“torso”) Mantle
Mouth, gut, heart, gill, reproductive organs
Mantle
Sheet of tissue attached to middle of back
Mantle cavity = space between mantle & visceral mass
Foot
Single muscular sheet contacts substrate
Creeps with 100’s of little muscles
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6. Phylum Mollusca Visceral mass (“torso”) Mantle Foot
Mantle cavity = space between mantle & visceral mass
Foot
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7. Phylum Mollusca Unique, distinguishing characters Mantle Foot Radula
Mantle cavity
Foot
Radula
Tooth-bearing scraping “jaw”
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8. Phylum Mollusca Ways the needs of cells are met Food
Scrape algae etc. or filter-feeders
Squids and Octopus are predators
O2 and CO2 exchange
Gills, or mantle cavity as “lung”
Waste removal
“kidney” with duct to mantle cavity
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9. Phylum Mollusca Style in “stomach”
Hard crystalline rod of digestive enzymes
Spins in stomach, wraps string of mucus and food
Ground away at posterior end along with mucus and food
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10. Phylum Mollusca Special concerns of a multicellular animal
Circulation: Open circulatory system
Coordination: Brain & ventral nerve cords,
Structural support: Hydrostatic &/or shell
Movement: Muscles in foot
Maintenance of water balance: “kidney”
Reproduction
Usually sexual, sexes usually separate, some hermaphrodites
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11. Phylum Mollusca Coelom reduced to pericardial cavity
Open Circulatory System
No blood vessels (almost)
Blood pumped forward through head, then oozes through visceral mass, around organs, muscles, gills, back to heart
Hemocoel
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12. Phylum Mollusca Nervous system Brain small, surrounds esophagus
Pair of visceral nerve cords
Pair of pedal nerve cords
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13. Phylum Mollusca Class Polyplacophora Class Gastropoda Class Bivalvia
chitons
Class Gastropoda
snails, slugs, nudibranchs
Class Bivalvia
clams, mussels, oysters, shipworm, etc.
Class Cephalopoda
squids, Octopus, cuttlefish, Nautilus
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14. Phylum Mollusca Class Polyplacophora Chitons
Thick mantle with eight shell plates
Scrape algae, etc. from rocks
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15. Phylum Mollusca Class Gastropoda snails, slugs, nudibranchs Torsion
Bending & twisting of gut
Conical, spiral shell
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16. Phylum Mollusca
Class Gastropoda
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17. Phylum Mollusca Class Bivalvia clams, mussels, oysters, etc.
Filter feeders
Gill used as filter
Radula usually lost
Shells on left, right
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18. Phylum Mollusca Class Cephalopoda
Octopus, Squids, Nautilus, cuttlefish,
Siphon on mantle edge
“rocket” away from predators
Tentacles with suction cups
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19. Phylum Mollusca Class Cephalopoda Octopus Complex behavior, learning
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