Phylum Mollusca

Class: Gastropoda

Class: Bivalvia

Characteristics of Mollusca

• Protosome characteristics • Coelom surrounds heart • Open circulatory system (except cephalopods)

Class Gastropoda

Snails, Limpets and Slugs

Gastropoda• Planning on being rich

and famous?• Wining and dining at the

most expensive restaurants?

• Romantic trips to Paris? • Ever wonder what

Ceaser munched on after long hard days ruling the roman empire?

• Than you should be familiar with ESCARGOT!!!!

General Body Plan: Gastropod

• 1. Head foot• Head: sensory nerves,

mouth – Anterior: near the

head/mouth

• Foot: attachment and locomotion – Posterior: near the anus– Flattened w Cilia:

locomotion

That slimy foot… • Snail Slime:

– Suction power: travel up and down trees

– Escape: Emit a nasty tasting slime when threatened

– Movement: Allows them to easily squeeze through tight spaces

– Water Retention• Ecological Roles:

– Skin regenerating – used in skin beauty

products

General Body Plan: Gastropod

• 2. Visceral Mass– Organs of

digestion – Circulation – Reproduction – Excretion – Dorsal to the

head foot

General Body Plan: Gastropod

• Mantle (shell) – Attached to visceral

mass• Encloses most of the

body – Protection

• Mantle Cavity: – Gas exchange– Elimination of digestive

wastes – Release of reproductive

products

Respiration

• One Gill in mantle cavity – Oxygen is taken in – Diffused through the cells

• Open Circulatory System – Pushes blood in to

expand– Pulls it out to contract

General Body Plan: Mollusca

• Radula: Scraping mouth – Chitinous belt & curved

teeth • Covers fleshy tongue • Muscles move it back

and forth • Conveyor belt

• Digestion – Scrape algae– Enzymes break down

food in stomach

• How do mollusks exchange gasses – Filter air through their gills

• Where are these gills located?– The mantel

• What is the structure called that scrapes up food?– A Radula

• All mollusks have: – A visceral Mass – A head foot – A mantel

Gastropoda

• Marine, Freshwater, Terrestrial • Signifying feature: Torsion

Torsion

• Benefits – Head enters first:

protection – Operculum seals

opening to prevent drying out

– Allows clean water to enter mantle cavity

– Makes snail more sensitive to stimuli coming from the front

Torsion

Reproduction

• Monoecious: can be whatever sex they want! – Internal cross

fertilization – One snail acts as

female one acts as male

– Deposit eggs in gelationous strings

CFU

• What is Torsion?– The 180 degree twisting of internal organs

in snails • How is Torsion adaptive?

– Pulls head in first, seals opening, locates all sensory nerves in the front

Class Bivalvia

Clams, Oysters, Mussles, Scallops

Bivalvia!

• Edible• Commercial value:

Form Pearls • Valuable in removing

bacteria from polluted water! – Rely on water currents to

get food – Filter in nutrients, filter

out clean water • Valuable food source:

humans, raccoons, otters, birds

Structure

• Two halves of a shell: Valves – Adductor muscles hold

valves shut • Visceral Mass• Mantel Cavity• Gills • Cilia• Siphon:

– filters water in and out of shell

Foot

• Most mollusks have foot that can be used differently – Attach mollusk to

surface – Act as a lure to

attract prey – Surround organs for

safety

Respiratory System

• Respiration: Cilia in gills move water into mantel cavity – Water tubes

exchange water to blood through diffusion

– Water exits bivalve

Digestive System

• Food comes in through gills – Sorted – Digested – Waste forcibly

pushed out of mantel cavity by valves shutting quickly

Human Interaction

• Many, many mollusks are threatened or endangered– Over harvesting– Pollution– Loss of habitat – Loss of water

currents

CFU • What is the technical term for the two halves

of the shell?– Valves

• What structure filters water in and out of the shell – Siphon

• What is the function of the foot – Attach mollusk to substrate, act as lure

• Why are bivalves important to humans?– Pearls, food source, pollution filter

• How are humans affecting bivalves? – Over harvesting, pollution, loss of current

Get ready for dissection!