PHYLA OF LESSER SIGNIFICANCE 



267 



are many morphological differences. The two halves of the shell repre- 

 sent dorsal and ventral surfaces rather than lateral, as in the mollusks ; 

 and within the shell there is a pair of spirally coiled arms which have no 

 counterpart in any other phylum. They are all marine and are able to 

 move about like the clams, but have a stalk coming out near the hinge of 

 the shell which they can use for temporary attachment. 



Photo by Winchester 

 Fig. 18.3. A moss animal, bryozoan. 



