86 INTRODUCTION TO ZOOLOGY CHAP. 



anterior segments of the body, and also many of the long 

 thread-like feelers or tentacles. 



Pectiriaria is another tube-worm that builds a 

 sandy case like that of Terebella conchilega, but 

 smaller, neater, and more compact, and therefore not so 

 flexible, also it has no marginal sandy fringe (Fig. 39, A). The 

 worms themselves (Fig. 4 1 ) can be easily recognised by the two 

 bunches of golden-coloured stiff bristles lying one x on each side 

 of the head : the short tentacles lie outside these bristles, and 



FIG. 40. The upper end of the empty FIG. 41. Pectinaria removed 



tube of Terebella conchilega. from its tube. 



(From the Cambridge Natural History.} 



on either side below the head are two pairs of short bladder- 

 like gills. The body ends in a little disc which closes the 

 narrower end of the tube. By means of its bristles the worm 

 burrows, head downwards, in the sand, the narrower end of 

 the tube alone projecting above the surface. 



Sabella is a worm which builds a tube of mud. 

 It is a social form, and clusters of the tubes of some 

 species of Sabella often exist side by side, and, with the sand 

 that gets washed in between them, cause the formation of 

 such firm masses that they can only be removed with a 

 hammer and chisel. The beautifully coloured gills are 



