646 Marvels of the Universe 
THE HOLOPUS 
This strange form has no stalk and is only affixed to the rock by the enlarged base of the cup. The limestone “‘armour”’ in 
Holopus is much thicker than in any other of the Sea-lilies. The living creature is possibly white, but after death it takes on a 
greenish hue. It has only been found at great depths in the Caribbean Sea. 
by the faultless contours of the joint. This latter principle, it will be remembered, is employed 
in the shell of the Sea-urchin, where the smooth edge of one division fits the smooth edge of 
the other, and the two are held together by little more than the marvellous accuracy of construc- 
tion. From each segment of the arm of a Sea-lily grows a tiny stalk or pinnule, and it is these 
pinnules branching from every segment of the arms that give the feathered appearance to the 
Crinoid. In the later-developed Crinoids the pinnules have been arranged to the right and left 
of the central groove of the arm on alternate segments, for the obvious purpose of sweeping the 
surrounding waters more effectively, and so of obtaining a greater supply of nourishment. In fact, 
the whole structure is arranged with this purpose in view ; even the long stalk serves to raise the 
cup and arms of the lily out of the restricted area of the sea-floor to a larger field of energy. The 
pinnules are very sensitive organs. In them are stored the immature ova. They are very sensitive 
to touch. As soon as they are aware of a strange presence they close down over the groove of the 
arm ; then the arms which stretch out star-like from the cup close up much in the same way as a 
flower closes its petals. As soon as the danger is apparently passed, the arms once more expand 
and the ceaseless movement of the pinnules commences again. 
But the variety in the forms and structures of Crinoids is immense. All are not stalked after 
the fashion of Thompson’s Sea-lily, which is shown on page 643. The Holopus, for instance (see 
above), has no stalk at all, and is only fixed to the sea-bed by means of the enlarged basal joint 
of the cup. Some of the stalks are provided at the junction of every ten segments with five little 
jointed feelers, or cirri ; others, such as the fossil species known as the Pear Encrinite, have a perfectly 
straight stem. Others, again, have “ roots ’’—that is to say, a bunch of branching cirri at the end 
of the stalk by which they support themselves in the mud ; while the majority fix themselves to the 
