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Learning Objectives
• By the end of this unit, students will be able to… • Describe the main characteristics of mollusks and the Mollusca four main groups, giving examples of each. • Describe the principal characteristics of annelids, giving Annelida examples of each group.
PHYLUM MOLLUSCA
“Mollusks”
Main classes of Mollusca Phylum Mollusca
• Polyplacophora • Mollusca is a very diverse phylum • Chitons • Characteristics • Gastropoda • Soft-bodied animals • usually covered by a shell • Snails, Slugs, etc. • Ventral foot • Bivalvia • for locomotion • Mantle • Clams, Bivalves, etc. • covers visceral mass (body • Cephalopoda organs)
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Phylum Mollusca Phylum Mollusca
• Circulatory system • Most have • most have an open system rasplike radula • Sinuses for feeding • Hemocoel - “blood cavity” • Bivalves are • Cephalopods have closed circulatory system suspension feeders
Trochophore Larva Class Polyplacophora (many plates)
• Most marine • Includes marine mollusks have chitons free-swimming, • Shells consist of 8 ciliated overlapping plates trochophore larva
• This larva is also found in the annelid worms.
Class Gastropoda (stomach foot) Class Gastropoda
• Largest group of mollusks • Body undergoes torsion • snails, slugs, nudibraches, and their relatives • a twisting of the visceral mass
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Class Bivalvia (shell has 2 halves) Class Bivalvia
• Includes aquatic clams, scallops, oysters, mussels
• Two-part shell
• hinged dorsally
• encloses bodies
Class Bivalvia CLAM • Often sessile • Suspension (filter) feeders • often found in large groups or “beds”
Digestive gland CLAM Heart CLASS CEPHALOPODA (HEAD FOOT) DORSAL Metanephridium Stomach Intestine Esophagus Posterior adductor muscle Ganglion Anus Anterior adductor muscle Excurrent siphon
Mouth Incurrent siphon Palp Gill—partially Pedal cut ganglion Mantle Foot Shell Intestine Gonad VENTRAL
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Class Cephalopoda Class Cephalopoda
• They are predators • Large brain • Active swimmers • Large eyes • 8 arms • Strong mouth • 2 tentacles • beak • hooks and suckers • radula
Class Cephalopoda Class Cephalopoda
Tentacles Internal (modified shell foot)
Digestive tract
Class Cephalopoda Class Cephalopoda
• Octopods • Nautilus • eight arms • external shell • smart
Mimic Octopus
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Class Cephalopoda Class Cephalopoda
• Cuttlefish • Squid • produce • eight arms hypnotizing colors • two tentacles for predation
• camouflage
Class Cephalopoda
• Giant Squid • Coevolution between predator and prey • Colossal Squid • better ways to catch prey evolve in predators • better ways to escape predator evolve in prey • large eyes to spot predators
“Evolutionary Arms Race”
Mimicry Mimicry
Cryptic Coloration
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Annelids
Cryptic Coloration
PHYLUM ANNELIDA (SEGMENTED WORMS) PHYLUM ANNELIDA (SEGMENTED WORMS) • Conspicuously long bodies • Aquatic worms • Segmentation • Earthworms • both internally and externally • Leeches
CLASSES OF ANNELIDA • Large, • Polychaeta compartmentalized coelom • Marine worms
• serves as hydrostatic skeleton • Oligochaeta
• Earthworms
• Hirudinea
• Leeches
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CLASS POLYCHAETA
Setae Mouth • Marine worms with parapodia
• appendages for Clitellum Suckers locomotion, gas exchange
• Parapodia have many Parapodia setae
• bristles or hair-like structures Anus Class Class Class Polychaeta Oligochaeta Hirudinea
CLASS POLYCHAETA CLASS OLIGOCHAETA • Well-defined head with • Earthworms sense organs
• unlike other annelids • Characterized by few short setae per segment
• Body divided into > 100 segments
• separated internally by septa
EARTHWORM
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CLASS HIRUDINEA • Leeches
• Characterized by absence of setae and appendages
• Parasitic leeches have suckers
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