168 THE DISTRIBUTION OF 
are eaten by the natives as food. The portion of the 
worm which remains behind in the coral reefs regener- 
ates the missing segments, and a year later the process 
is repeated. A similar process is suggested in certain 
British annelids, and is a device to ensure that the 
eggs are carried to a distance from the parent. 
The littoral annelids show many beautiful adapta- 
tions to shore life. We can only name the sea-mouse 
(Aphrodite), which lives buried in mud; Serpula, 
which secretes lime from the sea water and fashions 
a tube, which it attaches to rocks or to the hard parts 
of other animals or to weed; Terebella, which builds 
up tubes from the sand, and implants them deeply in 
the sand so that it is safe from the wash of the waves ; 
a Nereis, which lives inside the shell inhabited by 
a hermit crab, and thus finds protection from its 
enemies, and so forth. Very many of these annelids 
are greatly prized as food by fishes, and it is their 
abundance in the shore waters that attracts so many 
fish there. 
Very many of the echinoderms also are littoral, and 
manifest obvious adaptations to this mode of life. The 
sea-urchins burrow in the sand or mud, or else climk 
about the rocks by means of their suctorial tube feet. 
Starfish and brittle-stars similarly clamber over the 
bottom, while the holothurians either live buried in 
the sand or attach themselves by their tube feet. 
Not a few unsegmented worms are littoral, a pretty 
example being the turbellarian called Convoluta, which 
possesses symbiotic algae, a common feature of shore 
animals of simple structure. 
Perhaps the most interesting forms are, however, the 
Coelentera, which often show a double adaptation to 
littoral and to pelagic life. The fronds of the shore 
