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Terms in this set (63)

a) Class Polyplacophora- Chitons
- marine only
- 8 overlapping dorsal plates
- body is not segmented
- most are grazing herbivores living in shallow marine habitats ("plants")
b) Class Gastropoda-
- primarily marine (40,000 species)
- there are freshwater species
- only terrestrial mollusks are gastropods
* most gastropods have single shell, but some have lost their shell
* most gastropods creep on their foot, but in some the foot is modified for swimming
* head has pair of tentacles used for chemo- or mechanoreception, eyes are located at base of tentacles, some have second set of tentacles with eyes on end
* unique feature of gastropods is TORSION- twisting of body during larval growth so mantle cavity and anus are moved to front of body
c) Class Bivalvia: clams, mussels, cockles
- moat 10,000 species are marine
- some are freshwater
* no radula, no head
* wedge shaped foot for digging
* have two shells (valves)
* inhalant or incurrent siphon is where water enters brining food and oxygen
* exhalant or excurrent siphon is where water exits
d) Class Cephalopda: octopuses, squids, nautiluses
- more than 600 species
- marine only
- very active predators
* only mollusks with closed circulatory system
* foot evolved into arms with suction cups, adhesive devices, and hooks for capturing prey
* strong beak like jaws, radula, salivary glands
* largest relative brain size among invertebrates
* highly developed nervous system
* complex behavior patterns and highly intelligent
* cephalopod eyes similar to vertebrate eyes, but evolved separately
* no external shell, except for nautiluses, cuttlefish and squids have internal shell, octopuses have no shell
* move by jet propulsion when water that entered mantle is forced out through siphon
* ink sac, used as defense
* chromatophores in skin allow cephalopod to change colors for camouflage or communication
* cephalopods have direct development, that is no larval stage