Figure 2. — Exterior view of a scallop showing the result when a hydroid colony grows 

 faster than the scallop at successive periods and repeatedly overgrows the shell 

 perimeter. 



-\ 



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r- 



Figure 3. — Exterior and interior view of the upper (left) valve of a scallop showing 

 the hydroid partially covering and overgrowing the anterior part of the shell (arrows) 

 causing the scallop to change its shape as it grows in a direction away from the 

 hydroid. (Most fouling organisms were cleaned from the shell before the photo was 

 taken; only chitinous growths remain, including the colonial hydroid, worm tubing, and 

 filamentous hydroids.) 



276 



HYDRACTINA ECHINATA AND SHELL DEFORMITIES 



