Mollusca Short Answer Questions
Terms in this set (6)
Compare and contrast open and closed circulatory systems. Provide an example of Mollusc with an open circulatory system and an example of Mollusc with a closed circulatory system
A closed circulatory system has all the blood contained in vesicles and thus maintains a higher blood pressure. An open circulatory system does not contain all the blood in vessels and has less blood pressure. Cephalopods have closed systems.
Open- pumping heart, blood vessels, and blood sinuses(Chiton)
Closed- most cephalopods, have a heart, vessels, and capilllaries
Briefly describe locomotion in a typical terrestrial gastropod, a typical scallop and a typical cephalopod. Be sure to describe the role the foot plays (if any) in each mollusc.
The typical motion of a scallop is that of a clapping motion. The scallop uses adductor muscle to contract both of the bivalve halves together in order to create movement through the water. The foot does not aid particularly in the movement of the bivalve.
Briefly describe each of three strategies freshwater mussels use to facilitate the transmission of their glochidia larvae to a fish host. Of the three strategies, which is most susceptible to turbid (cloudy) water? Why?
Some mussels simply release glochidia into the water where they must haphazardly come into contact with the appropriate fish host as it swims by.
→ Females in the mussel genus Lampsilis have an extension of the mantle tissue that strikingly resembles a small fish. The mussel displays this tissue outside its shell between the valves and twitches it repetitively to attract its predaceous fish host - like a fishing lure. While attempting to eat the lure, the marsupial gills of the female mussel are ruptured, and the fertilized eggs come loose and attach themselves to the fish - the host fish is infected.
→ Other mussel species release small structures containing glochidia called conglutinates. These float freely into the water. Conglutinates look like prey items to the host fish; the host fish are infected when they attempt to eat them.
1. The Lure Strategy: Pregnant female lures fish by wiggling mantle flaps that look like small minnows
2. The Bait Strategy: Bags or larvae are reeled out at the end of a line
3. The Net Strategy: Release long filament strands that intertwine to form nets.
Question: Why are freshwater mussels indicators of clear water?
A: If they are more visible, than their reproductive strategies are more efficient
Briefly describe the process of torsion in Gastropods. What possible benefit(s) does torsion confer? What is one drawback to torsion? Briefly describe each of the three adaptations Gastropods possess to deal with this particular drawback. One of these adaptations is related to coiling (and may actually be an exaptation). Briefly describe coiling, tracing its "four step" evolution as outlined in figure 10.14. Provide one benefit and one drawback for each of these four steps.
At beginning of a Gastropod's life, at the tiny larval stage (the veliger), the parts of the body begin to rotate. Not of all them, just the organs for digestion, reproduction, circulation, the shell, and the body wall that covers the former and secretes the latter, twist 180˚ counter clockwise. This process, called torsion, eventually places the organs previously on the right side on the left.
-More space in mantle cavity allows the head to be withdrawn into the shell with tougher foot forming a barrier
-Sensory organs in mantle cavity better positioned to sample water at anterior end
Fouling can occur when waste washes over gills
1)Makes a cleft in shell and mantle for current, this is bilaterally symmetrical, but not compact
2)Apex of shell drawn out, more compact but less balances
3)Shell is shifted upwards and posteriorly, this is more balanced but puts pressure on some organs
4)Shell is shifted farther over body for better balance but loses right gill and kidney
Briefly describe three different ways Gastropods feed. Be sure to describe the role the radula plays in each type of feeding strategy.
Herbivores "rasp" algae from a substrate; some graze and others feed on plankton
Cone snails harpoon prey with a venomous radular tooth
Moon Snails use radula to bore holes into bivalve shells and arthropods
Describe three Cephalopod adaptations that allow them to escape predators.
-- Jet Propulsion
-- Ink Ejection
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