SYNOPSES OF NORTH-AMERICAN 
INVERTEBRATES. 
XV. THE HOLOTHURIOIDEA. 
HUBERT LYMAN CLARK. 
THE holothurians form a sharply defined group of marine 
invertebrates, especially abundant in the tropics but well repre- 
sented in both temperate and polar seas. About six hundred 
species are known, varying in size from ten millimeters to 
almost a meter in length, and some of the largest species are 
thirty or forty centimeters in circumference. The colors vary 
greatly but generally are not brilliant, some shade of brown 
or gray being the most frequent. Red, however, of various 
shades is not rare, and green and yellow are also not infrequent. 
Wholly black or white forms are not uncommon. The shape 
is often worm-like but is more commonly broader and thicker, 
often resembling a cucumber, so that the name “sea cucum- 
bers ” is frequently given to the group. They are found at all 
depths, from high-water mark to the bottom of abysses 2900 
fathoms from the surface. They are generally sluggish in 
their movements, and very few forms have any means of rapid 
locomotion. They feed almost wholly on the organic matter 
found in the mud or sand where they live, though a few species 
found among rocks seem to feed upon organic matter growing 
on the rocks or brought to them in the water. Some species, 
especially the large ones, live on the bottom where it is muddy 
or sandy, creeping about very slowly and apparently molested by 
few enemies, Others, especially the footless forms, live buried 
In the mud or sand, where they burrow by means of their ten- 
tacles and muscular movements of the body wall. Still others 
dg under or among rocks, often snugly stowed away in some 
ole or crevice, where they seem to be permanently settled and 
whence they can only be dislodged by breaking the rock. 
479 
` 
