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Lab 7 - Exam Review (Phylum Mollusca).docx

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Biology (Sci)
BIOL 111
Suzanne Gray

Lab 6 Invertebrates II Phylum Mollusca  Second only to arthropods in terms of number and diversity  Example: terrestrial gastropod (brown garden snail) Cantareus aspersus  Herbivorous, feeding on terrestrial vegetation External Anatomy: very strong foot, therefore difficult to pick up when attached to a surface  Shell: composed of CaCO and3proteins secreted from the mantle o Many species have a hard dark disk, called an operculum, on the dorsal surface of their foot; when retracted, this structure acts like a lid, sealing the snail within its shell  Foot: controls locomotion; specialized glands produce and secrete mucus along which the snail grips and slides o Mucus produced by the foot can be used to reduce water loss, lo allow strong adhesion to a substrate and to form egg cases produced after fertilization  Tentacles: two pairs of tentacles on their head; used for olfaction (smell/taste). Chemoreceptors are located within the tentacles epidermis: o The shorter the inferior tentacles are used to detect chemicals on the ground o The longer superior tentacles are used to detect airborne chemicals (possess photoreceptors at their tips)  Does a snail have an operculum? No  On which pair of tentacles are the eyes located? Superior tentacles Locomotion: four different ways locomotion may be achieved 1. Monotaxic: the wave of contractions can extend across the width of the foot 2. Ditaxic: can alternate between the right and left sides 3. Direct waves: involves the lifting of the posterior edge of the foot and forward placement, followed by a forward wave of contractions 4. Retrograde waves: involves the lifting of the anterior edge of the foot, the stretching and attachment of it in a more forward location and a backward wave of contractions  What type of locomotion does the snail use? Monotaxic; direct
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