Phylum Mollusca I

Question 1

Chiton characteristics present in other molluscs and others that are unique to Polyplacophora

Answer 1

Similar: 
CaCO3 shell secreted by mantel tissue
Ribbon of radular teeth
The mantle cavity contains ctenidia and osphradia and receives the anus, nephridiopores and gonopores 
Bipectinate ctenidia
Muscular foot on ventral side
Unique: 
8 shell plates 
Minimal cephalization
Dorso-ventral flattening
Mantle assists with substrate adhesion
Radula with caps of magnetite

Question 2

Anatomical characteristics of torsion

Answer 2

Development of a spiral shell that arose from a planar flattened shell.
This results in the anus of the animal being above the head
Reduces with shell aperture, # of shell muscles, # of ctenidia
Either due to a 180 degrees twist or a loss and expansion of mantle cavity

Question 3

Difference between stenoglossate and flexoglossate and which groups have which

Answer 3

Stenoglossate radula do not flex laterally - simple rasp
Flexoglossate radula do flex laterally
All gastropods except for Patellogastropods have flexoglossate
Chitons have flexoglossate