Molluscs Flashcards
What do the molluscs include?
Snails, squids and scallops.
What clade are the Molluscs in?
The Lophotrochozoa
Diversity of the Molluscs?
Second biggest phylum with 100,000 species.
Features of molluscs?
Evolutionary flexible body plan. Through gut. Not segmented. Shell and mantle, therefore gills. Radula
Describe the shell of Molluscs?
The shell is secreted by tissue called the mantle. The shell is made of extracellular calcium carbonate plus proteins. The conchin protein precipitates the calcium carbonate. The direction of the crystals dictates the properties.
What is a radula?
A special feeding structure. A ribbon with teeth which is pulled tight over a solid block of cartilage called the odontophore.
Orders of Molluscs?
Gastropods. Bivalves. Cephalopods.
Describe the main features of gastropods?
Have one shell, which is sometimes lost. Uses the radula to scrape algae off rocks/eat lettuce.
Slow moving grazers.
Torsion: Body twists 180 degrees anticlockwise. Body twist not shell twist.
This means that waste products are excreted over the head/sense organs. Some solve this with having a hole in the shell.
Why have some gastropods lost their shell?
Have different defences.
Land slug - slime
Modify the radula into a hypodermic harpoon for poison.
Describe the main features of bivalvia?
Have two shells, with a foot between and no radula.
Foot can fill with blood to allow for burrowing.
W shaped gills with 1000s of cilia, for a massive water current.
Ligament opens the shells.
Either sessile or slowly burrowing. Some reduce the shell to become worm like and eat wood. Others invent eyes (up to 60).
Describe the main features of Cephalopods?
The molluscs which can swim. “The fish of the invertebrate world”.
Original cephalopod - chambered shell and slow swimming.
More advanced - closed blood system, large brain, well developed eyes, shell reduction, jet propulsion (water squirted from mantle cavity) and are active hunters.
