BIOL 111 Lecture Notes - Hectocotylus, Ink Sac, Dendrite
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5 Apr 2012
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18/10/11
Mollusca:
2nd 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