Phylum Phylum MolluscaMollusca

“soft-“soft-bodied”bodied”

•4 Primary Classes

–Class Gastropoda: Snails, conchs, slugs, sea slugs, sea hares, limpets, etc. (very diverse)

Gastropoda: “stomach-footed”Gastropoda: “stomach-footed”Snails and slugsSnails and slugs

Class Bivalvia:

Clams, oysters and scallops

Bivalvia: “two halves”Bivalvia: “two halves”Clams, oysters, scallops, Clams, oysters, scallops,

musselsmussels

Class Cephalopoda:

Octopi, squid, nautilis, cuttlefish

Cephalopoda: “head-footed”Cephalopoda: “head-footed”Octopi, cuttlefish, squid, nautaliOctopi, cuttlefish, squid, nautali

http://www.youtube.com/watch?feature=player_detailpage&v=YVvn8dpSAt0

Blue-Ring Octopus

Cuttlefish

Squid

Giant SquidGiant SquidAvg. length:Avg. length:

35 feet 35 feet Max. Max.

Length:Length:80 feet80 feet

Colossal SquidColossal SquidMaximum Maximum

length:length:43 feet 43 feet

http://www.ted.com/talks/david_gallo_shows_underwater_astonishments.html

Class Polyplacophora:

Chitons

Body planBody plan• Bilateral Symmetry• Muscular foot used for locomotion,

burrowing and capturing prey • Mantle, an outgrowth of tissue that covers most of it’s body. This secretes the shell.• Coelom -Body cavity primarily around heart• Shell - Made of calcium carbonate, internal

or external• Viceral mass – the internal organs

FeedingFeeding• Complete digestive system • Herbivores use a radula to scrape

algae from rocks• Carnivores use jaws to eat prey like the octopus• Filter feeders use a siphon to catch

plankton

•Gas exchange via gills, lungs

•Land snails respire through a mantle or its body surface

RespirationRespiration

• Open circulatory system- except cephalopods, where the blood is transported through the body via a cavity called the hemocoel

• Leaving the vessels, blood travels through sinuses or large sack-like spaces

• Possess blood vessels by a heart• Fast moving mollusks have a closed

circulatory system using blood vessels

CirculationCirculation

ExcretionExcretion

• Tube shaped nephridia remove ammonia from the blood and release it outside the body

ResponseResponse

• Nervous system varies greatly. Other than cephalopods, it is very basic. Several ganglia in clams and bivalves

• Cephalopods have a highly developed brain and nervous system, near equal to vertebrates.

MovementMovement

• Some secrete mucus• Others like the octopus move by jet

propulsion

ReproductionReproduction

• Reproduction is sexual by external fertilization as in snails and bivalves

• Some are hermaphroditic like the snail

Ancestry of Ancestry of MolluscsMolluscs

Phylum SignificancePhylum Significance• Eaten for food by humans and other animals.

Clams, oysters, scallops, mussels, (shellfish) snails (escargot), octopus and squid are popular foods

• Research - i.e. snails appear to be cancer free • Indicators of environmental pollution • Land snails and slugs damage gardens and crops • Shipworms destroy wooden boats, docks, and piers. • Filter feeders can concentrate toxins through

biological magnification (Humans eating them can become ill or even die).