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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

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CLASS HIRUDINEA • Leeches

• Characterized by absence of setae and appendages

• Parasitic leeches have suckers