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