Phylum Phylum MolluscaMollusca

IntroductionIntroductionMollusk – slugs, snails, Mollusk – slugs, snails, octopus, squid, clam, oysteroctopus, squid, clam, oyster50,000 living mollusk species 50,000 living mollusk species and about 35,000 fossil and about 35,000 fossil species. species. The number of known species The number of known species is second only to the Phylum is second only to the Phylum Arthropoda. Arthropoda.

IntroductionIntroductionThe majority of mollusks are The majority of mollusks are marine, but large numbers marine, but large numbers of species occupy of species occupy freshwater and terrestrial freshwater and terrestrial habitats.habitats.Some mollusk swim while Some mollusk swim while others are sedentary. others are sedentary.

IntroductionIntroductionOysters produce pearls. Oysters produce pearls. Some mollusk shells are Some mollusk shells are highly valued by collectors. highly valued by collectors. In times past these shells In times past these shells were used as money and were used as money and today are used ornamentally today are used ornamentally for such items as buttons for such items as buttons and jewelry. and jewelry.

Common characteristics Common characteristics shared by molluskshared by mollusk Soft, flexible bodySoft, flexible body Bilateral symmetryBilateral symmetry Eucoelomates (body cavity Eucoelomates (body cavity containing internal organs)containing internal organs)

--Digestive system with two Digestive system with two body openings – a mouth body openings – a mouth in the head and the anus in the head and the anus emptying into the mantle emptying into the mantle cavity.cavity.

Most have a radula (except Most have a radula (except bivalves). The radula is bivalves). The radula is usually toothed (may be a usually toothed (may be a single or could be single or could be thousands) and is adapted thousands) and is adapted for scraping, tearing, for scraping, tearing, stabbing, and cutting. stabbing, and cutting. In some the teeth are hollow In some the teeth are hollow and poison-containing and and poison-containing and are used as weapons.are used as weapons.

Thick muscular foot, Thick muscular foot, primarily used for primarily used for locomotion locomotion Mantle (thin membrane Mantle (thin membrane surrounding coelom); also surrounding coelom); also secretes the shell in those secretes the shell in those forms that possess one.forms that possess one.

A well-developed head, which A well-developed head, which may bear sensory tentacles may bear sensory tentacles (except bivalves)(except bivalves)An open circulatory system An open circulatory system (except cephalopods, which is (except cephalopods, which is closed) with a heart, blood closed) with a heart, blood vessels, and hemocyanin.vessels, and hemocyanin.

When oxygenated such blood When oxygenated such blood is bluish in color; when is bluish in color; when deoxygenated the blood is deoxygenated the blood is colorless. colorless.

Respiration - Gas exchange Respiration - Gas exchange is via gills, lungs, or the is via gills, lungs, or the body surface. body surface. Secrete mucus – uses Secrete mucus – uses include locomotion, food include locomotion, food entrapment, and prevention entrapment, and prevention of water loss.of water loss.

Classes of Mollusks (3 of 7)Classes of Mollusks (3 of 7)1.Gastropoda –includes 1.Gastropoda –includes snails, limpets, slugs, snails, limpets, slugs, conchsconchs2.Bivalvia – oysters, clams, 2.Bivalvia – oysters, clams, scallops; made of two scallops; made of two hinged shells,hinged shells,3.Cephalopoda – squid, 3.Cephalopoda – squid, octopus, nautilusoctopus, nautilus

GASTROPODS GASTROPODS - largest - largest and most diverse class and most diverse class (about 40 000 or 80%);(about 40 000 or 80%);Most have a single coiled Most have a single coiled shell (made of calcium shell (made of calcium carbonate) into which the carbonate) into which the body can be withdrawn. body can be withdrawn. Shells vary in color, shape, Shells vary in color, shape, ornamentation, and size ornamentation, and size according to the species. according to the species.

Slugs are shell-less. Shells Slugs are shell-less. Shells range in size form range in size form microscopic to a 24 inch microscopic to a 24 inch marine snail ( marine snail ( Pleuroploca Pleuroploca giganteangigantean). A sea hare, ). A sea hare, AplysiaAplysia,, can reach 3 ft. can reach 3 ft.

Feeding Habits – Many are Feeding Habits – Many are herbivores (snails), with herbivores (snails), with multi-toothed radulas for multi-toothed radulas for scraping algae from various scraping algae from various substrates. substrates. Some are carnivores – Some are carnivores –

feeding on small fish, worms, feeding on small fish, worms, plankton and on smaller plankton and on smaller mollusks.mollusks.

The conch feeds on fish and The conch feeds on fish and annelid worms that they first annelid worms that they first paralyze with poison paralyze with poison contained in their hollow contained in their hollow radula teeth. The poison is radula teeth. The poison is also toxic to humans, also toxic to humans, causing paralysis and causing paralysis and sometimes death.sometimes death.

Muscular foot is used for Muscular foot is used for movement in most species. movement in most species. Reproduction Reproduction terrestrial – hermaphroditesterrestrial – hermaphrodites Aquatic – external fertilizationAquatic – external fertilizationNervous system – simple; Nervous system – simple; small brain; nerves small brain; nerves coordinate movement and coordinate movement and behavior.behavior.

BIVALVESBIVALVESTwo shells, of similar size, Two shells, of similar size, held together by a hinge held together by a hinge ligament coming together at ligament coming together at the the umbo;umbo; shell covers soft shell covers soft body; muscles open and body; muscles open and close (adductor muscle) close (adductor muscle)

Shells can range in size – Shells can range in size – the freshwater seed shells the freshwater seed shells are among the smallest are among the smallest know, being less than 0.1 know, being less than 0.1 inch in length, while the shell inch in length, while the shell of the giant clam may of the giant clam may exceed 4 ft in length (500 exceed 4 ft in length (500 lbs).lbs).No distinctive head or radulaNo distinctive head or radula

Feeding habits – most are Feeding habits – most are sedentary filter feeders. sedentary filter feeders. Draw water in, water moves Draw water in, water moves over the gills, then exits over the gills, then exits through; as waste moves through; as waste moves over gills, food and over gills, food and sediment trapped in the sediment trapped in the mucus is sorted and then mucus is sorted and then eliminatedeliminated

Most have a single pair of Most have a single pair of gills for respiration and for gills for respiration and for trapping minute food trapping minute food particles.particles.Separate sexes with Separate sexes with external fertilization.external fertilization.Most are marine, but many Most are marine, but many live in brackish water in live in brackish water in streams, ponds, and lakes.streams, ponds, and lakes.

CEPHALOPODS CEPHALOPODS – “head-– “head-footed”footed”Most complex of the Most complex of the mollusks. All are marine.mollusks. All are marine.Have tentacles w/suckers Have tentacles w/suckers instead of a single foot. instead of a single foot. They are used for They are used for movement and capturing movement and capturing food. food.

Have radula and sharp, Have radula and sharp, beak-like jaws to tear apart beak-like jaws to tear apart food. They are carnivorous. food. They are carnivorous. Eating fish, bivalves and Eating fish, bivalves and crabs.crabs.Have a closed circulatory Have a closed circulatory system. system.

Only the nautilus has a Only the nautilus has a shell. shell. Move by jet-propelled Move by jet-propelled swimming (66 ft/second)swimming (66 ft/second)Reproduction –Internal Reproduction –Internal fertilization, then eggs are fertilization, then eggs are laid. Tentacles transfer laid. Tentacles transfer sperm into female’s body.sperm into female’s body.

Nervous system – Nervous system – Complex brain w/ ability Complex brain w/ ability to learn (capturing prey to learn (capturing prey or avoiding harmful or avoiding harmful situations). Highly situations). Highly developed sense of developed sense of visionvisionRespiration – gillsRespiration – gills

Most have chromatophores, Most have chromatophores, special pigment cells, in special pigment cells, in their skins, which allow their skins, which allow them to change color them to change color rapidly. May have a sac rapidly. May have a sac that secretes an ink-like that secretes an ink-like substance called sepia; this substance called sepia; this is expelled when the animal is expelled when the animal is alarmed, hiding the is alarmed, hiding the animal as it flees.animal as it flees.

Cephalopods are worldwide Cephalopods are worldwide in distribution and are found in distribution and are found in all depths of the oceanin all depths of the ocean..