Phylum Mollusca

•75000 species•2nd only to Phylum Arthropoda•Includes octopuses, oysters, snails, slugs, squids, clams…•Divided into 6 classes based on shell and foot

Common Characteristics

• Shell ~ tough multilayered structure, for protection or body support• Mantle ~ sheath of tissue that encloses vital organs,

secretes its shell and forms its respiratory structures• Visceral hump ~ contains its heart, digestive, and

excretory organs, covered by mantle• Foot ~ fleshy, muscular organ used for locomotion• Radula ~ small organ covered with tiny teeth that

scrapes up food particles and draws them into mouth.• Trochophore- ciliated larval form

3 Mollusk Classes• Bivalvia – two

shelled mollusks• Gastropoda -

stomach footed mollusks

• Cephalopoda – head footed mollusks

Clam Nutrition and Digestion

•Filter feeders- feed on organic material strained from the water•Bivalves lack a radula•Siphons- tubes used to filter water over the clams body•Palps- pair of lobelike organs surrounding the mouthoGills and palps secrete a stringy, sticky mucus that

catches the food•Cilia move food to the mouth•Digestive system also includes a stomach, digestive gland, intestines, and anus

Class Bivalvia:Two-Shelled

Mollusks

Clams, oysters, mussels, scallops

Clams•Clams secrete shiny material around an irritating foreign object forming a pearl•Foot is used for locomotion and burrowing•Can also move by rapidly opening and closing shell which causes it to bounce along the seafloor•Nervous system including ganglia, nerves, and various sensory organs including as many as 100 simple eyes along the margin of the valve that can detect light and movement•Sexual reproduction

Circulation and Respiration

• Open circulatory system including a heart and a kidney which filters waste from the blood• Respiratory system including gills- thin walled

ciliated structures richly supplied with blood vessels where oxygen and carbon dioxide are exchanged

Class Gastropoda: Stomach-Footed

Mollusks

•Snail, slugs, nudibranchs•The foot is immediately below the visceral hump which is where the stomach is located.

Nudibranch Videoshttp://www.youtube.com/watch?v=cJE-LPcwtP8http://www.youtube.com/watch?v=V6H01cUSpfQ

Nutrition and Digestion• Eats plant material• Scrapes food with tonguelike radula• Torsion- body develops into twisted, asymmetrical

arrangement unique to gastropods, anus is close to anterior region of the body, above the mouth

Respiration

•Mantle cavity• space between the mantle lining, the shell, and the

animal’s soft body•Thickly supplied with blood vessels and functions as a lung

in respiration

Locomotion

• Lays down a layer of slime• Glides on slime by rhythmical contractions of its

muscular foot (10ft per hour)

Response

•Series of ganglia around the head region•Pair of eyes at the end of two tentacles•Other receptors for smell, touch, and chemical detection located in the head and foot

Class Cephalopoda: Head-Footed Mollusks

Octopus, squid, nautilus, cuttlefish

Class Cephalopoda•The foot extends from the head region•The foot is usually divided and contains suckers•Squids eyes are much like mammalian eyes and are capable of very accurate vision.•Amazing camouflage and mimicry abilities

http://www.youtube.com/watch?v=1VjxvrXGEHkhttp://www.youtube.com/watch?v=t-LTWFnGmeghttp://www.youtube.com/watch?v=3pDVScNCkiIhttp://www.youtube.com/watch?v=7NQUqR_YpsA