MOLLUSKS: Slugs, snails, and animal that once lived in shells in the ocean or on the beach. Slugs, snails, and animal that once lived in shells in the ocean or on the beach. Phylum Mollusca Phylum Mollusca Range from slow-moving slug to jet- propelled squid Range from slow-moving slug to jet- propelled squid Found in oceans, freshwater and moist terrestrial habitats Found in oceans, freshwater and moist terrestrial habitats

Oysters and mussels live firmly attached to the ocean floor or to the bases of docks or wooden boats. Oysters and mussels live firmly attached to the ocean floor or to the bases of docks or wooden boats. Squid and the octopus swim freely Squid and the octopus swim freely Slugs and snail crawl slowly over the forest floor. Slugs and snail crawl slowly over the forest floor.

species species Some have shells Some have shells Bilateral symmetry Bilateral symmetry True coelom True coelom Two body openings Two body openings Muscular “foot” for movement Muscular “foot” for movement Mantle: thin membrane that surrounds the internal organs of the mollusk Mantle: thin membrane that surrounds the internal organs of the mollusk In mollusks with shells, the mantle secretes the shell. In mollusks with shells, the mantle secretes the shell.

How mollusks obtain food: Radula: located within the mouth of a mollusk, is a tongue-like organ with rows of teeth. Radula: located within the mouth of a mollusk, is a tongue-like organ with rows of teeth. The radula is used to drill, scrape, grate or cut food. The radula is used to drill, scrape, grate or cut food. Some mollusks are grazers, some are predators, and some are filter feeders. Some mollusks are grazers, some are predators, and some are filter feeders. Bivalves do not have radulas, they are filter feeders. Bivalves do not have radulas, they are filter feeders.

Reproduction in Mollusks: Most have separate sexes and reproduce sexually. Most have separate sexes and reproduce sexually. Eggs and sperm are released at the same time into the water where external fertilization takes place. Eggs and sperm are released at the same time into the water where external fertilization takes place. Many gastropods are hermaphrodites. Many gastropods are hermaphrodites. Having the same individual produce both sperm and eggs increases the likelihood of fertilization in slow-moving animals. Having the same individual produce both sperm and eggs increases the likelihood of fertilization in slow-moving animals.

Nervous Control in Mollusks: Simple nervous system with a brain and associated nerves that coordinate movement and behavior. Simple nervous system with a brain and associated nerves that coordinate movement and behavior. Paired eyes that range from simple cups that detect light to complex eyes in the octopus that have irises, pupils and retinas and function as well as the human eye. Paired eyes that range from simple cups that detect light to complex eyes in the octopus that have irises, pupils and retinas and function as well as the human eye.

Circulation in Mollusks: Well-developed circulatory system with a three-chambered heart. Well-developed circulatory system with a three-chambered heart. Open circulatory: blood is pumped through vessels and into open spaces surrounding organs. Open circulatory: blood is pumped through vessels and into open spaces surrounding organs. This exposes organs directly to blood containing oxygen and nutrients and easily removes wastes. This exposes organs directly to blood containing oxygen and nutrients and easily removes wastes.

Some mollusks (such as the octopus) has a closed circulatory system. Some mollusks (such as the octopus) has a closed circulatory system. Closed circulatory system: blood moves through the body enclosed in a series of vessels Closed circulatory system: blood moves through the body enclosed in a series of vessels

Respiration in Mollusks: Most mollusks have respiratory structures called gills. Most mollusks have respiratory structures called gills. Gills increase the surface area through which gases can diffuse. They are an extension of the mantle. Gills increase the surface area through which gases can diffuse. They are an extension of the mantle. In land snails and slugs, the mantle has evolved into a primitive lung. In land snails and slugs, the mantle has evolved into a primitive lung.

Excretion in Mollusks: Oldest known animals to have evolved excretory structures called nephridia Oldest known animals to have evolved excretory structures called nephridia Nephridia: organs that remove metabolic wastes from an animal’s body. Nephridia: organs that remove metabolic wastes from an animal’s body. Mollusks have one or two nephridia that collect wastes from the coelom. Mollusks have one or two nephridia that collect wastes from the coelom. Wastes are discharged into the mantle cavity, and expelled from the body by the pumping of the gills. Wastes are discharged into the mantle cavity, and expelled from the body by the pumping of the gills.

Diversity of Mollusks: Seven classes Seven classes These are the improtant 3 These are the improtant 3 –Gastropoda –Bivalvia –Cephalopoda

Gastropods: One-shelled mollusks One-shelled mollusks Largest class Largest class Stomach-footed (named for the way that the large foot is positioned under the body) Stomach-footed (named for the way that the large foot is positioned under the body) Slugs have not shell Slugs have not shell Snails, abalones, conches, periwinkles, whelks, limpets, cowries and cones Snails, abalones, conches, periwinkles, whelks, limpets, cowries and cones

May be found in freshwater, saltwater, or moist terrestrial environments. May be found in freshwater, saltwater, or moist terrestrial environments. May be plant eaters, predators or parasites. May be plant eaters, predators or parasites.

Slugs: No shell No shell Body is protected by a thick layer of mucus. Body is protected by a thick layer of mucus. Nudibranchs: colorful sea slugs Nudibranchs: colorful sea slugs Nudibranchs feed on jellyfish and incorporate their nematocysts into their own bodies which are expelled whenever a predator tries to feed on the slug. Nudibranchs feed on jellyfish and incorporate their nematocysts into their own bodies which are expelled whenever a predator tries to feed on the slug.

Bivalves: Two-shelled mollusks Two-shelled mollusks Clams, oysters and scallops Clams, oysters and scallops Most are marine, but a few a freshwater. Most are marine, but a few a freshwater. Range in size from 1 mm to 1.5 meters Range in size from 1 mm to 1.5 meters No distinct head or radula No distinct head or radula Most use their muscular foot for burrowing in the mud or sand at the bottom of the ocean or lake. Most use their muscular foot for burrowing in the mud or sand at the bottom of the ocean or lake.

A ligament like a hinge connects the two shells. A ligament like a hinge connects the two shells. Filter feeders Filter feeders Cilia beat to draw water into an incurrent siphon. Cilia beat to draw water into an incurrent siphon. As water moves over the gills, food and sediment are trapped in mucus. Cilia that line the gills push the food particles into the stomach. As water moves over the gills, food and sediment are trapped in mucus. Cilia that line the gills push the food particles into the stomach.

The cilia also act as a sorting device. The cilia also act as a sorting device. Any rejected material is transported to the mantle where it is expelled through the excurrent siphon. Any rejected material is transported to the mantle where it is expelled through the excurrent siphon.

Cephalopods: Head-footed mollusks Head-footed mollusks All marine All marine Octopus, squid, cuttlefish, and chambered nautilus Octopus, squid, cuttlefish, and chambered nautilus

The only cephalopod with a shell is the chambered nautilus. The only cephalopod with a shell is the chambered nautilus. The cuttlefish has a reduced internal shell. The cuttlefish has a reduced internal shell. Very complex structures Very complex structures Predators that swim or walk over the ocean floor pursuing their prey. Predators that swim or walk over the ocean floor pursuing their prey. They grab prey with their tentacles. They grab prey with their tentacles.

The foot has evolved into structures with hooks, suckers or adhesive structures. The foot has evolved into structures with hooks, suckers or adhesive structures. The tentacles bring the prey to the mouth where it is bitten by the beak-like jaw. The tentacles bring the prey to the mouth where it is bitten by the beak-like jaw. The food is then pulled into the mouth by the radula. The food is then pulled into the mouth by the radula.

Possess siphons that expel water. Possess siphons that expel water. By expelling water forcefully, these mollusks can move quickly by jet propulsion. By expelling water forcefully, these mollusks can move quickly by jet propulsion. Squids can attain speeds of 20 meters per second with this method. Squids can attain speeds of 20 meters per second with this method. They also expel “ink” to confuse and escape predators. They also expel “ink” to confuse and escape predators.