58 Animal Life by the Sea-shore. 



together under the name of Serpuhds ; in them, not only is the 

 tube formed of hard calcareous matter, but the whole organisa- 

 tion of the animal is modified to subserve a tubicolous existence ; 

 the head, for instance, has been transformed into a collar-like 

 structure provided with a crown of long gill-filaments. The 

 tubular, shell-like tubes of Serpula (Fig. 72) and its near relatives 

 have a circular aperture which can be closed by one of the gill- 

 filaments, enlarged to form an operculum. The tubes so often 

 found on emptj? shells of various molluscs belong to the allied 

 genus Pomaioceros ; these differ from those of Serpttla in having a 

 longitudinal, keel-like ridge. Spirorhis borealis (Fig. 73) secretes a 

 spiral tube very similar to the shell of a gastropod mollusc ; such 

 " shells," measuring less than an eighth of an inch across, 

 are commonl}? found attached to stones or other hard objects, 

 or to the fronds of sea-weeds. The head of the worm is similar 

 to that of Serpula, but the operculum formed by one of the 

 gill-filaments is hollow, and performs the unexpected function 

 of a brood-pouch, receiving and storing the eggs during the 

 breeding season. 



On some parts of our coasts tubicolous Annehds are suffi- 

 ciently abundant to form quite a characteristic feature of the 

 landscape. At Whitsand Bay, near Plymouth, as well as at 

 other places, especially on the South Coast, the sandj' tubes 

 of Sabellaria alveolaia constitute thick, rock-like masses several 

 feet in diameter, the animals being gregarious, and building 

 their tubes in close contact, like the pipes of an organ. 

 Sabellaria is peculiar in bending its body in two so as to bring 

 the much-narrowed posterior extremity to open close to the 

 mouth of the tube. 



On lifting up stones or examining the tangled roots of 

 Laminarian seaweeds examples of a quite different t\'pe of worms 

 are often met with, remarkable for their great tenuity and the 

 absence of anj? trace of segmentation, of feet, bristles or other 

 kinds of appendages. Such worms belong to the group of 

 Long Worms or Nemerteans, of which Linens marinus is a good 

 example. Only from one to four lines in breadth, this species 

 has a length of fifteen to thirty feet when fully developed, a 

 length which is, however, not apparent owing to the close, 

 twisted coils into which the body is thrown. There is no 

 distinct head, the anterior, blimted extremity of the soft body 

 carrying the mouth, through which a thin, trunk-like proboscis 

 can be protruded. Linens contracts to an extraordinary extent ; 

 a specimen several yards in length may shrink to as many inches, 

 and the changes in width are equally striking. Professor 



