Mollusks

Mollusk Vocabulary Word Definition foot mantle siphon An appendage that some invertebrates use to move. mantle A layer of tissue that covers the body of many invertebrates; secretes a shell. siphon A hollow tube of mollusks, used for sucking in and expelling sea water.

What is a Mollusk? Photo credit: NOAA

Characteristics Soft-bodied coelomates 3 part body plan Visceral mass Mantle Foot Bilateral symmetry MOST have a shell

Mollusk Body Plan Visceral mass: central section of a mollusk’s body  contains the organs

The Mantle Layer of tissue that covers the body of many invertebrates: secretes a shell Univalve: 1 shell Bivalve: 2 shells Photo credits: MSC

The Foot Muscular region; used for movement

Organ Systems: Digestion Clams (filter feed) All mollusks (except bivavles) have a radula. Radula – a rasping, tonguelke organ that is covered with “teeth”; used for feeding by many mollusks

Circulation & Respiration 3 chambered heart Most mollusks breathe with gills Open circulatory system Terrestrial snails – membrane that lines the snail’s mantle = basic lung Octopi – closed circulatory systems Some sea snails = diffusion through skin

Reproduction Male & female individuals Snails & slugs = hermaphrodites Fertilized eggs of most mollusks  trochophore Trochophore – free-swimming ciliated larvae

3 Major Mollusk Classes

Gastropods – (Snails & Slugs) Marine, freshwater, & terrestrial habitats Pair of tentacles on their head – eyes at the tips Mucus comes from their foot – glide along Use radula to scrape off food

Cephalopod – “head foot” Foot = tentacles (w/ suction cups or hooks) Squids = 10, octopi = 8 Most intelligent of all invertebrates Complex nervous system Siphon – “jet propulsion”, also release “ink” What are CHROMATOPHORES!? Ex: Octopus, squid, nautilus

Bivalves Two-part, hinged shell Flattened body between two shells Most are filter feeders (gills to filter food) Pearl Production – grain of sand gets stuck betweent he mollusk’s mantle & shell Coat with nacre (mother-of-pearl); shiny substance Ex: Clams, oysters, scallops, mussles