Molluscan

Charateristics

• Bilateral
• Soft bodies
• Coelomate
• most have a shell
• Mantel drapes over body secretes shell
• Most have fleshy foot
• Have radula for shredding food
• Dieocious (males and females)

Nine Classes

• Class Caudofoveata (deep-sea wormlike creatures; 70 known species); now generally recognized as a subclass of Aplacophora.
• Class Aplacophora (solenogasters, deep-sea wormlike creatures; 250 species)
• Class Polyplacophora (chitons; 600 species, rocky marine shorelines)
• Class Monoplacophora (deep-sea limpet-like creatures; 11 living species)
• Class Bivalvia (also Pelecypoda) (clams, oysters, scallops, mussels; 8,000 species)
• Class Scaphopoda (tusk shells; 350 species, all marine)
• Class Gastropoda (nudibranchs, snails and slugs, limpets, sea hares; sea angel, sea butterfly, Sea Lemon; estimated 40,000 - 150,000 species)
• Class Cephalopoda (squids, octopuses, nautilus, cuttlefish; 786 species, all marine)
• Class † Rostroconchia (fossils; probably more than 1,000 species; probable ancestors of bivalves)

Gastopoda

• Snails
• Slugs
• Sea Slugs (nudibranches "no shell-gills")
• Aphysia- colorful sea slugs used in physilogical experiments found in the Mediterraian Sea
• Torsion- digestive system twisted 180 degrees during velogar larval stage
• limpet- prehistoric gastropoda with two wholes to circulate water
• viseral mass- holds gonads, digestive gland, "kidney", and heart
• have eyespotes
• can have tenticals
• slugs have fleshy projections, called ctenidia

Torsion __________________________________________Body Plan

Polyplacphora

• Marine animals
• found on shores and in coral reefs
• Chiton (bearing many plates)
• 

Bivalvia

• Bivalves
• Clams
• Oysters
• abductor muscls keep shells closed
• rings on shell are formed each year, Number of rings = age of clam
• umbo - hinge
• no radula
• no head
• gills are ciliated with mucus, to catch microscopic organisms for food
• female releases eggs that are caught in their gills, males release their sperm in the water, and are taken in by female's syphons and are caught in gills where eggs are fertilzed
• incurrent syphon - to intake water for circulation
• exurrent syphon
• zebra mussles- invasive species that deplete the food chain of plankton
• blue mussle- attach to things by byssal theads a protien
• radula- assists in scraping food
• mantel secretes shell
• three parts of shell
  • outter- peristraicum- makes the shells color and patter
  • middle layers of prismatic or chrystilne layer made of CaCo3 and conchiolin a protien matrix
  • inner layer- nacre- mother of pearl
• Perals are formed in all bivalves
• Color depends on species
• a particle gets between shell and mantel and irritates mollusk, which secretes nacre which covers irritating particle
• muscular foot- mobile divice
• gueliger larva
• economic value
  • buttons
  • gravel
  • "Native American money"
  • food
    • scallops
    • clams
    • oysters
    • escargot
    • calamari

Clam dissection

Test yourself

Slide 49 Clam glochidium larva

Cephalopoda

• adapted to be active predators
• streamline swimmers
• move by jet propultion- water is forced out of muscular mantel cavity through a funnel shaped siphon
• large brain- relative to body size
• developed eyes that form images
• closed circulatory system
• chromatophore cells, (pigment-bearing cells) for camaflage
• beak and radula for predation
• differ from clams because digestive gland secretes fluid that can pralize small animals
• predatory animals
• foot developed ams with suckers
• some have the ability to change color
• Octopus
  • 8 arms
  • inksac- defensive mechanism
  • 2 branchela hearts, for speeding blood through the gills
• Nautilus
  • only cephalopod that retains shell
  • secretes gases in shell so they can float, for feeding
• Squids
  • fastest aquatic animal
• Chesapeak Bay squid

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