THE BRACHIOPODS 
N long past ages these creatures were far more abundant than 
mollusks, and their shells are among the commonest fossils of the 
oldest rocks. Now, however, they are nearly all extinct, and. are 
usually found only at considerable depths, or along tropical shores. 
At first sight one would mistake these animals for clams or mus- 
sels, but they are more closely related to worms than to mollusks. 
In Brachiopods the two halves of each shell on either side of a 
middle line are similar, whereas in clams and mussels the two 
halves of each shell are not alike in shape. 
A still greater difference, which has been discovered through 
careful study, is that the shells of the Brachiopods grow on the 
back and lower side of 
the animal and the 
head faces the gape of 
the shell, whereas in 
the mollusks the shells 
grow on the right and 
left sides, and the 
ventral side of the body 
faces the gape of the 
shell. ‘The mouth in 
the Brachiopods is 
flanked by two curi- 
ously coiled and feath- 
ered arms which lie 

within the cavity be- 
tween the shells, and 
are supported by skel- 
Fig 43; Parchment Shells growing upon a stone. From “we 
a depth of 160 feet off Gloucester Harbor, Mass. etal rods attached to 
the upper shell. These 
serve as gills and also to capture the minute creatures upon which 
the Brachiopod feeds. In Brachiopods the posterior end of the 
body is sometimes stalk-like and projects backward either through 
