Phylum Mollusca “soft- bodied”

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

Gastropoda: “stomach-footed” Snails and slugs

Class Bivalvia: Clams, oysters and scallops

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

Class Cephalopoda: Octopi, squid, nautilis, cuttlefish

Cephalopoda: “head-footed” Octopi, cuttlefish, squid, nautali player_detailpage&v=YVvn8dpSAt0

Blue-Ring Octopus

Cuttlefish

Squid

Giant Squid Avg. length: 35 feet Max. Length: 80 feet

Colossal Squid Maximum length: 43 feet

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Class Polyplacophora: Chitons

Body 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

Feeding 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 Respiration

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 Circulation

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

Response 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.

Movement Some secrete mucus Others like the octopus move by jet propulsion

Reproduction Reproduction is sexual by external fertilization as in snails and bivalves Some are hermaphroditic like the snail

Ancestry of Molluscs

Phylum 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).