--------------- Fri. Feb. 14 (cont.) -------------
• 1) A sound monophyletic phylum, 2nd most diverse (named species!)

  • a) seven classes of living species (3 major, 4 minor)

  • b) widespread in all major habitats: marine- all classes, freshwater- gastropods & bivalves, terrestrial- gastropods
  --------------- Mon. Feb. 24 -------------

• 2) Soft, fleshy body has four regions (head, foot, viscera, mantle with calcareous shell) and two unique characters (ctenidium, radula)

• 3) Most have an extensive mantle cavity (between mantle & body) that may serve many functions (respiration, feeding, locomotion)

  • a) the mantle produces new shell by accretionary growth at the edge

  • b) a unique ciliated gill (bipectinate ctenidium) pumps water locomotion or feeding

  • c) an individual may have one to many ctenidia depending on taxon
  --------------- Wed. Feb. 26 -------------

• 4) Most possess a unique feeding structure: the radula

  • a) flexible ribbon studded with many rows of chitinous teeth

  • b) complex muscles move ribbon back & forth over an odontophore

• 5) Possess two fluid-filled cavities in mesoderm: coelom & hemocoel

  • a) coelom usually very reduced (surrounds heart, gonad & kidneys)

  • b) hemocoel is extensive: blood is pumped through spongy tissues

  • c) hemocoel functions as circulatory system & hydrostatic skeleton

• 6) Spiral cleavage yields a distinct embryo with a "molluscan cross"; most have a trochophore larva, some pass through a veliger stage
  --------------- Fri. Feb. 28 -------------

• 7) Class GASTROPODA (snails & slugs)

  • a) largest class is divided into 3 subclasses: Prosobranchia (marine snails), Opisthobranchia (sea slugs), Pulmonata (land snails)

  • b) have a single, usually coiled shell; single or paired ctenidia

  • c) have a large, creeping foot; most move using muscular waves

  • d) primitively were rasping grazers, but feeding ecology is diverse

  • e) united by a bizarre developmental process: torsion (twisting of posterior end over head)

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