142 MOLLUSCA 



AMPHINEURA 

 CHAETOPLEURA (Chiton) 



It will be profitable to study only external features, unless 

 time is to be had for cutting and studying sections, as the 

 species is small and difficult to dissect. Its apparently gen- 

 eralized structure, and its adaptations, make it desirable for 

 students to understand from descriptions and figures the main 

 features of its anatomy. 



1. Examine specimens that are attached to stones and 

 shells and see how nicely they adapt their shapes to the 

 shapes of the objects to which they are attached. How is 

 this possible? 



2. Remove a specimen and quickly transfer it to a clean 

 glass slide, applying its ventral side to the glass. Put your 

 finger in its back and prevent it from curling for a minute. 

 It will then generally remain attached to the slide and may be 

 studied from both sides. 



3. How many plates are there? What is the shape of 

 each? Do they apparently join edge to edge or do they 

 overlap? Do the plates extend clear to the margin of the 

 animal? What reason is there for having plates instead of 

 a solid dorsal shell? 



4. Notice the thickened margin of the animal, and see 

 that dorsally it bears spicules, while ventrally it is smooth 

 and is applied closely to the slide. 



5. Notice the flattened elliptical foot. Do you understand 

 how the animal creeps and adheres? 



6. In front of the foot is the head fold in which the mouth 

 can be seen. 



7. In the furrow bordering the foot are the gills. 



8. Remove the animal from the slide and see how it curls 

 up. Try to unroll it. Explain. 



9. If you care to see the radula, the organ that especially 

 indicates affinity to the Gastropoda, it can be pulled out by 

 grasping just behind the mouth with pointed forceps and 





