84 INTRODUCTION TO ZOOLOGY CHAP. 



about at the bottom of deep muddy pools. It lives beyond 

 low tide mark but is sometimes thrown up into shallow water, 

 and so is named after the Greek goddess 

 concerning whom the legend runs that she 

 was born of the waves. The sea-mouse 

 is peculiar on account of the thick covering 

 of long fine hairs over the upper side of 

 its flattened oval body, which may be as 

 much as 6 inches long, but is usually a 

 good deal smaller. The whole body is 

 generally covered with mud when it is 

 picked up, but, if it is washed in a clean 

 pool, the very beautiful iridescence of 

 the hairs and bristles will become ap- 

 parent. 



Sedentary A very large number of 

 forms, the sea -worms are not free- 

 (Sedentaria). swimming j^ se d en tary (Se- 



dentaria or Tubicolae). For the protection 

 of the body, these worms form a tubular 

 structure, which they either build up from 

 the mud, sand, or shells around them, 

 binding them together with a sticky sub- 

 stance exuded from their own bodies, or 

 they make the whole tube of a calcareous 

 matter which they themselves secrete (e.g. 

 Serpula, Fig. 43). In a few cases they 

 merely burrow in the sand and mud. 

 FIG. 38. The Paddle- . The Common Lugworm or 



worm (Phyttodoce ' Lobworm (Arenicola marina), 



used so much by fishermen for bait, is one 

 of these burrowing forms. It is 8 or more inches long, 

 and its colour is black or brownish-green, partly due to the 

 large quantity of dark-coloured mud that it swallows in 

 burrowing and from which it extracts its food. At every 

 low tide on nearly every sandy and muddy sea -coast, the 

 presence of these lugworms is indicated by the great number 

 of castings or " sand-ropes " lying on the surface. 



Terebella is a case-building form. One species, 



llla " the Sand Mason (T. conchilega), builds a little flexible 



tube of sand and pieces of shell, with a fringe of sandy threads 



