Phylum Mollusca What is a mollusk PHYLUM MOLLUSCA

Phylum Mollusca

What is a mollusk? • PHYLUM MOLLUSCA • __________________are all mollusk. • There is a wide variety of animals in this phylum—from the slug that moves very slow to the squid who is jet-propelled. • Most species live in the ______, but some live in freshwater and moist land habitats. • Some mollusks, such as oysters, live most of their lives attached to the ocean floor or a boat that has sunk. • Others, like the octopus, swim freely in the ocean.

Phylum Mollusca • Some mollusks have ______, and others do not. • All mollusks have ________symmetry, a __________________digestive tract, a muscular foot, and a mantle. • The mantle is a membrane that surrounds the internal organs of the mollusk. • In mollusks with a shell, the mantle secretes the shell.

A. How Mollusks Obtain Food • Most mollusks have a structure called a ________ that helps them obtain food. • This structure is located within the mouth. • It is a tongue-like organ with rows of _______ • It is used to drill, scrape, grate, or cut food.

A. How Mollusks Obtain Food • Octopus and squid are _________ that use their radulas to tear up the food they capture with their ___________. • Other mollusks are grazers and some are filter feeders.

B. Reproduction in Mollusks • Mollusks reproduce ___________. • In most aquatic species, eggs and sperm are released at the same time into the water, where _________ fertilization occurs. • Many mollusks that live on land are hermaphrodites, with internal fertilization. • Some marine mollusks have free-swimming larvae that propel themselves by cilia.

C. Nervous Control in Mollusks • Mollusks have simple nervous systems that coordinate their movement and behavior. • Some more advanced mollusks have a _______. • Most mollusks have paired eyes that range from simple cups that detect light (oscelli) to the complex eyes of an octopus that have irises, pupils, and retinas similar to the eyes of humans.

D. Circulation in Mollusks • Mollusks have a well-developed circulatory system that usually includes a ___________heart. • In most mollusks, the heart pumps blood through an _______ circulatory system. – the blood moves through vessels and into open spaces around the body organs. • This adaptation exposes body organs directly to blood that contains nutrients and oxygen, and it also helps remove wastes from cell activites.

D. Circulation in Mollusks • Some mollusks, such as octopi, move nutrients and wastes through a _______ circulatory system. – blood moves through the body enclosed entirely in a series of blood vessels. • This system provides an efficient means of gas exchange within the body.

E. Respiration in Mollusks • Most mollusks have respiratory structures called _______. • These are specialized parts of the mantle that have a rich supply of blood for the transport of gases. • Gills increase the ___________ through which gases pass.

F. Excretion in Mollusks • Mollusks are the oldest known animals to have structures called nephridia. • These are organs that remove waste from an animal’s body. • Mollusks have one or two nephridia that collect waste from the coelom, which is located around the heart only. • Wastes are discharged into the mantle cavity, and expelled from the body by the pumping of the gills.

Diversity of Mollusks • Most of the common and well-known species of mollusk are in 3 classes: – Class Gastropoda – Class Bivalvia – Class Cephalopoda

A. Gastropoda • This is the largest class of mollusks. • They are also called the “_______” mollusks. • This name comes from the way the animal’s large foot is positioned under the rest of its body.

Gastropoda • Most members of this class have a _______ but some do not. • Some of the animals that do have a shell are abalones, conchs, periwinkles, whelks, limpets, cowries, and cones. Some of these have the ability to shoot a “_______” to kill prey. • These may be plant eaters, predators, or parasites.

Gastropoda • A slug is one example of a gastropod that does not have a shell. • It is protected by a thick layer of mucus.

Gastropoda • Colorful sea slugs, called nudibranches, are protected in a different way. • When sea slugs eat jellyfish, they take in the poisonous nematocysts into their own tissues. • Any fish that tries to eat the sea slug will get stung by these nematocysts. Wow… a flashback to Protists maybe? Showing evolutionary symbiosis?

B. Bivalvia • • • These are mollusks with _______ shells. Some examples are clams, oysters, and scallops. Most bivalves are marine. They have no distinct head or radula. Most use their large, muscular foot for burrowing in the mud or sand at the bottom of the ocean. • A ligament, like a hinge, connects their two shells (valves) and strong muscles allow the valves to open and close over the body. • One of the main differences between gastropods and bivalves is that bivalves are ______________.

C. Cephalopoda • This class is the “_______ mollusks. • It includes octopus, squid, cuttlefish, and the chambered nautilus. • The only cephalopod with a shell is the chambered nautilus.

Cehphalopoda • In this class, the foot has evolved into tentacles with suckers, hooks, or adhesive structures. • They swim or walk over the ocean floor after their prey, capturing it with their tentacles. • Once tentacles have captured prey, it is brought to the mouth and bitten with strong _____ (Rotifera anyone? ). • Then the food is torn and pulled into the mouth by the radula.

Cephalopoda

Cephalopoda • Like bivalves, cephalopods have _______ (pumps) that expel water. • They can expel water in any direction and move quickly. • Squids can get up to speed of 20 m/s using this system of movement. • Squids and octopi also can release a dark fluid to cloud the water. • This “ink” helps to confuse their predators so they can make a quick escape.