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Phylum Mollusca

Phylum Mollusca. Head, visceral mass, muscular foot, and thin mantle that covers the body and secretes the shell Class Gastropoda: snails and limpets Class Bivalvia (Pelycypoda): mussels and clams. Gastropoda. Aquatic Gastropoda. In N.S. 15 families, ~500 species Two suborders

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Phylum Mollusca

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  1. Phylum Mollusca • Head, visceral mass, muscular foot, and thin mantle that covers the body and secretes the shell • Class Gastropoda: snails and limpets • Class Bivalvia (Pelycypoda): mussels and clams

  2. Gastropoda

  3. Aquatic Gastropoda • In N.S. 15 families, ~500 species • Two suborders • Prosobranchia-gilled snails • Pulmonata-lunged (pouch) snails • Mouth has a radula, a ribbon of rasping teeth • Gilled snails have operculum (trap door cover) Sinistral Dextral

  4. Natural History • Most are scrapers • Gilled snails respire by an internal gill • Pulmonate snails have a pouched gill; many come to surface to breathe surface air, hence can tolerate low oxygen conditions • Reproduction: most gilled snails have separate sexes; most pulmonates are hermaphroditic • Egg masses often resemble blobs of mucous • Development is within the egg; hatch as small snails with only 1-2 whorls (most adults have3-4) • Some are intermediate hosts for human parasites • Are food for many aquatic vertebrates (crush) and invertebrates (invade) • Bioindicator status: • Gilled snails-sensitive to facultative • Pulmonate snails-most are tolerant

  5. Bivalvia • ~270 freshwater species in N.A. • Two shells connected by strong hinge ligament

  6. Anatomy

  7. Bivalve Natural History • Most abundant and diverse in moderate current in medium to large rivers; • US is center of origin • Intolerant of siltation and low oxygen • All are filter feeders of suspended algae, bacteria, and detritus • Filtering mechanism doubles as a gill

  8. Reproduction Glochidium-for dispersal, not nutrition

  9. Species of Note • Fingernail clams release large, developed young; this smallest of clams produces the largest of eggs and juveniles • Asian Clam-introduced; • 1st observed in 1938 • Cannot tolerate cold

  10. Zebra Mussels, Dreissena polymorpha

  11. Veliger

  12. Endangered Unionids Cracking Pearlymussel Northern Clubshell White Wartyback Fat Pocketbook Rough Pigtoe

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