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BIOL 111 (283)
Lecture

Mollusca and Nervous System

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Department
Biology (Sci)
Course
BIOL 111
Professor
Irene Gregory- Eaves
Semester
Fall

Description
18/10/11 Mollusca: 2 largest phylum - Terrestrial/aquatic - High diversity: morphology, modes of nutrition, reproduction - Bilaterally symmetrical, trioblastic - Coelomate protostomes - Trochophore larcae (marine) - Variation on an ancestral molluscan Morphology: 1. Foot: often used for locomotion, sometimes have cilia, secretes 2. Mantle: secretes CaCO3 layer 3. Mantle cavity: allows water to com in and out, breathe through modified gills 4. Visceral mass: a. Radula: series of corrugated, toothed, serrated to rasp across the ground to feed, predation, Diversity: 1. Polyplacophore: many plates – series of places over lapping, not as hard as snail shells - Oldest: burgess shale (520-560 million years old - Multiple gills - Omnivorous, but not predatory Ex. Chiton: - Large muscular foot - Ability to roll into ball - Gills located in mantle gills 2. Bicalvia: two valves - Reduced of head some have vestigial eyes or brain - Hinged shells can open and close - Enlargement of foot: used to burrow through the ground and anchorage - Siphons: in current/out current: filter feeders, pulls out small nutrient - Enlarged gills - Sessile in adult phase - Broadcast spawners - Vissel thread associated with foot (secreted by foot) - If under sedement can extend siphon up to filter water Ex scallop: - Lined with eyes: can detect motion and light, fly through the water 3. Gastropoda: - Most diverse within mollusca (terrestrial marine, fresh water, deep ocean, in trees) - Long fossil record in Burgess Shale 18/10/11 - Can be shelled (snails), shelless (slugs, nudibranchs) - Hebivorous, omnivorous - Dioecious or hemaphradidic – but can only produce sperm of eggs at one time - Mouth and anus are close each other - Mantle cavity right above head - Torsion: body/shell orientation spin left of right: elongation of shell occurs Ex. Cone snail: have harpoon that comes out the front = radula modified to be toxic Ex. Nudibranch: exclusively marine: gills = specialized filaments accorss bodies Ex. Land snails: image forming eyes on tips of tentacles, elongated feet 4. Cephalopoda: head foot – have multiple arms/tentacles on their heads - Shell is often absent, or present in the body – reduced shells, enlarged head for skeleton like thing - Subdivided foot = arms or tentacles
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