MOLLUSCA Phylum Mollusca (mollusks) clam, snail, octopus, squid.
Phylum Mollusca
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Transcript of 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
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
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
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
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