Mollusca Flashcards
For mollusca, most animal diversification at phylum/class occurred ……
Prior to the cambrian explosion!
What is the difference between parallel and countercurrent flow for gas exchange?
Parallel flow: where water and blood flow in the same direction, and the concentration of oxygen will reach an equilibrium. Limits the amount of oxygen extracted from water
Countercurrent: Water and blood flow in opposite directions, oxygen concentration gradient is maintained. Supports higher active lifestyle
All molluscs, except for cephalopods, have what kind of gas exchange?
countercurrent flow
Why do cephalopods NOT have countercurrent flow?
- cephalopods move by thrusting water in and out, and they do not have a singular directional water exchange so do not need counter current flow
What are the 7 main classes of mollusca?
- polyplacophora
- aplacophora
- monoplacophora
- gastropods
- bivalvia
- scaohopoda
- cephalopoda
What are polyplacophora?
- class within mollusca
- less than 1000 species, all marine
- have a shell made of 7-8 plates
- grazers, with a body plan adapted to hold onto substrate
What are aplacophora?
- class within mollusca
- fewer than 400 species, all marine
- no fossil record because they are worm-like with no true shell
- body is covered in spicules, move similar to turbellarians
what are monoplacophora?
- class within mollusca
- fewer than 50 species, all marine
- until the mid 20th century, only known from their fossils
What are gastropods?
- class within mollusca
- most diverse class in the phylum
- all have shells as an ancestral trait
What are the two defining characteristics of class gastropoda?
- torsion: developmental characteristic where anterior and posterior viscera become twisted 180 degrees
- operculum: “door” of shell. Used to close opening of shell
