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 fresh- water mussel 



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(Materials: aquaria, carmine suspension.) "v^ |^ )^ 



Classification : — Phylum Mollusca, Class Acephala. 



The mussel is studied as an example of a highly developed 

 group of animals which are entirely without segmentation. 



Despite the very great diversity of size and form among the 

 numerous species and genera of mussels, all follow the same plan 

 of structure closely enough to permit the application of the fol- 

 lowing outline of study to any of the common species found in 

 our lakes and streams. 



I. The Live Animal 



1. Note the general appearance and position of the animal 

 when fully extended. 



2. Identify the fleshy foot, and the tivo valves which com- 

 prise the shell. Note the gaping valves caused by the tension of 

 the hinge ligament. 



3. The foot projects from the lower (ventral) anterior 

 part of the shell and the hinge line is on the dorm.l surface. 



4. At the posterior end of the animal distinguish the in- 

 halent aperture by means of carmine suspension. Determine the 

 function of this opening. Is there an exhalent aperture? If so, 

 give the evidence for this. Notes required. 



5. Examine the demonstration of a fragment of a gill under 

 the microscope and observe the movement of the cilia. How is 

 the water current produced? What are its main functions? The 

 food of the mussles consists primarily of microscopic plant forms 

 (plankton) and particles of organic matter suspended in the 

 water. 



6. Make an outline drawing, natural size, of the expanded 

 condition of the animal and name all parts. 



93 



