CHAPTER XIII 

 BARNACLES AND OTHER CRUSTACEANS 



THE ship's barnacle looks at first, when you see 

 one of a group of them hanging from a piece of 

 floating timber, like a little smooth, white bivalve shell, 

 as big as your thumb-nail, at the end of a thickish, 

 worm-like stalk, from one to ten inches long (Fig. 10). 

 But you will soon see that there are not only two valves 

 to the white shell, but three smaller ones as well as the 

 two principal ones. This does not separate them alto- 

 gether from the bivalve-shelled molluscs (mussels, clams, 

 oysters), for the bivalve molluscs, which bore in stone 

 and clay, have small extra shelly plates, besides the two 

 chief ones, whilst the Teredo, or ship's worm — a true 

 bivalve mollusc — has an enormously long, worm-like 

 body which favours a comparison with it of the long- 

 stalked barnacle. If a group of barnacles is floating 

 attached to a piece of timber undisturbed in a tank of 

 sea-water you will see the little shells gape, and from 

 between them a bunch of curved, many-jointed feelers 

 will issue and make a succession of grasping or clawing 

 movements, as though trying to draw something into the 

 shell, which, in fact, is what they are doing — namely, 

 industriously raking the water on the chance of bringing 

 some particle of food to the mouth which lies within the 

 shell (Fig. io). 



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